{"id":3518,"date":"2022-03-02T15:53:41","date_gmt":"2022-03-02T15:53:41","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/?post_type=chapter&#038;p=3518"},"modified":"2022-04-08T04:15:38","modified_gmt":"2022-04-08T04:15:38","slug":"what-to-know-about-2c","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/chapter\/what-to-know-about-2c\/","title":{"raw":"What to Know About 2C: Experimental Design","rendered":"What to Know About 2C: Experimental Design"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>learning GOALS<\/h3>\r\nAt the end of this page, you should feel comfortable performing these skills:\r\n<ul>\r\n \t<li>Identify the factor of interest and response factor in an experiment.<\/li>\r\n \t<li>Identify the nuisance factors in an experiment.<\/li>\r\n \t<li>Identify the experimental and control groups in an experiment.<\/li>\r\n \t<li>Recognize random assignment.<\/li>\r\n \t<li>Identify which of two methods of replication was used in an experiment.<\/li>\r\n<\/ul>\r\n<\/div>\r\nExperimental design refers to the structure of an experiment (a specific type of research method). How can the experiment be conducted efficiently, effectively, and responsibly, to return sound results? Researchers must carefully consider several key components of experimental design before any work is done to collect data.\r\n\r\nIn the upcoming activity, you will need to identify the key components of experimental design. We'll take them one by one in the following questions.\r\n<h2>Experimental Design<\/h2>\r\nAn experimental study, or experiment, is a specific method of research that is especially useful for determining cause and effect. Typically, a basic experiment design includes a treatment imposed by the researcher, a comparison between one group that receives the treatment and another group that does not, and random assignment of participants into each group. We\u2019ll explore each of these concepts in more detail below.\r\n\r\nTo help you understand the key components of experimental design, consider this simplified experiment:\r\n\r\n<span style=\"background-color: #ffff99;\">[insert an image of a lake? fish eggs? pH strips?]<\/span>\r\n\r\n<em>An ecologist wants to know if acid rain affects the rate of reproduction for fish in a local lake. The ecologist incubates 1,000 fish eggs in healthy lake water (pH = 6.5) and another 1,000 fish eggs in acidic water (pH = 4.5). The eggs have been randomly assigned to either the healthy lake water group or the acidic water group. The water temperature, amount of dissolved oxygen, and amount and timing of light were kept at optimal levels for both groups. After 14 days, the ecologist counted how many eggs from each group had hatched.<\/em>\r\n\r\nEach of the questions below will ask about aspects of the design present in this experiment.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>question 1<\/h3>\r\nA good experiment always starts with a good research question. For an experiment, the research question is usually about whether one thing causes another. Fill in the blanks below to summarize the ecologist\u2019s research question.\r\n\r\n\u201cDoes ______________________ cause ________________________?\u201d\r\n\r\n[reveal-answer q=\"727621\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"727621\"]What does the ecologist want to know? What is the specific cause and effect the ecologist is investigating?[\/hidden-answer]\r\n\r\n<\/div>\r\n<h3>Factors<\/h3>\r\nIn an experimental study, the <strong>factor of interest<\/strong> (also known as the <strong>explanatory variable<\/strong> or independent variable) is the factor that the researcher purposely changes or manipulates to see if it impacts a specific outcome. The <strong>treatments<\/strong> are the different levels of the factor of interest (or explanatory variable) you are changing (e.g., no vaccine vs. vaccine).\r\n\r\nThe <strong>response variable<\/strong> (also known as the <strong>dependent variable<\/strong>) is an objective measure of the research question that is measured at the end of an experiment and compared across the different levels of the factor of interest (or explanatory variable).\r\n\r\n<img class=\"alignnone wp-image-1391\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5738\/2022\/01\/14234115\/Picture192-300x67.jpg\" alt=\"A small flowchart. The first box says &quot;Factor of Interest \/ Explanatory Variable.&quot; There is an arrow beside it labeled &quot;affects&quot; going to the second box, labeled &quot;Response Variable.&quot;\" width=\"1294\" height=\"289\" \/>\r\n\r\nThe <strong>nuisance factors<\/strong> are factors that are kept the same across all levels of the factor or are explicitly controlled in the experimental design. These factors are not of interest in the study but may affect a change in the response variable.\r\n<div class=\"textbox tryit\">\r\n<h3>Video Placement<\/h3>\r\n<span style=\"background-color: #e6daf7;\">[A video briefly describing factor of interest, treatment, response variable, and nuisance factors. This should be no more than a minute long. ]<\/span>\r\n\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Example<\/h3>\r\nSummarize the terminology surrounding factors by answering the questions below.\r\n<ol>\r\n \t<li>The factor of interest is also known as the _________________. Fill in the blank.<\/li>\r\n \t<li>The response variable is also known as the ________________. Fill in the blank.<\/li>\r\n \t<li>What does the researcher purposely change or manipulate to see if it impacts a specific outcome? Choose all that apply\r\n<ol>\r\n \t<li>a) experimental factor<\/li>\r\n \t<li>b) explanatory variable<\/li>\r\n \t<li>c) response factor<\/li>\r\n \t<li>d) factor of interest<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>What are treatments in an experiment?\r\n<ol>\r\n \t<li>a) medicine applied to one set of individuals but not the other<\/li>\r\n \t<li>b)\u00a0the different levels of the factor of interest (or explanatory variable) you are changing<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>What are nuisance factors in an experiment?\r\n<ol>\r\n \t<li>a) types of observational units that are particularly bothersome such as loud talkers<\/li>\r\n \t<li>b) types of factors that researchers are unable to account for in an experiment<\/li>\r\n \t<li>c)\u00a0factors that are kept the same across all levels of the factor or are explicitly controlled in the experimental design<\/li>\r\n<\/ol>\r\n<\/li>\r\n \t<li>What is measured at the end of an experiment and compared across the different levels of the factor of interest?<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"54865\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"54865\"]1. explanatory variable; 2. dependent variable; 3. b and d; 4. b; 5. c; 6. the response variable[\/hidden-answer]\r\n\r\n<\/div>\r\nNow you try. Use the definitions given above to answer Question 2. Remember to view the feedback for your answers to assess your understanding.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>question 2<\/h3>\r\nIdentify the different parts of the experimental design in the previous simplified experiment.\r\n\r\nPart A: What is the factor of interest?\r\n<ol>\r\n \t<li>a) pH level<\/li>\r\n \t<li>b) Temperature<\/li>\r\n \t<li>c) Oxygen level<\/li>\r\n \t<li>d) Amount of light<\/li>\r\n \t<li>e) Timing of light<\/li>\r\n \t<li>f) Incubation duration<\/li>\r\n \t<li>g) Number of eggs hatched<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"344691\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"344691\"]Which factor did the ecologist purposely change?[\/hidden-answer]\r\n\r\n&nbsp;\r\n\r\nPart B: What is the response variable?\r\n<ol>\r\n \t<li>a) pH<\/li>\r\n \t<li>b) Temperature<\/li>\r\n \t<li>c) Oxygen level<\/li>\r\n \t<li>d) Amount of light<\/li>\r\n \t<li>e) Timing of light<\/li>\r\n \t<li>f)\u00a0 Incubation duration<\/li>\r\n \t<li>g) Number of eggs hatched<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"821608\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"821608\"]Which factor did the ecologist measure at the end of the study?[\/hidden-answer]\r\n\r\n&nbsp;\r\n\r\nPart C: What are the nuisance factors in the previous experiment? There may be more than one correct answer.\r\n<ol>\r\n \t<li>a) pH<\/li>\r\n \t<li>b) Temperature<\/li>\r\n \t<li>c) Oxygen level<\/li>\r\n \t<li>d) Amount of light<\/li>\r\n \t<li>e) Timing of light<\/li>\r\n \t<li>f) Incubation duration<\/li>\r\n \t<li>g) Number of eggs hatched<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"861184\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"861184\"]Which factors did the ecologist keep the same for both groups?[\/hidden-answer]\r\n\r\n<\/div>\r\n<h3>Controls<\/h3>\r\nAn important aspect of all experiments is a comparison between one or more groups or <strong>levels<\/strong> of the factor of interest, called <strong>treatments<\/strong>. In a simple experimental design, one group receives the researcher\u2019s treatment and the other group(s) does not. The group that receives the treatment is commonly called the experimental group. The group that does not receive the treatment is usually called the control group. The control group is usually kept under conditions that are considered typical or common for a given situation.\r\n\r\n<img class=\"alignnone wp-image-1112\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5738\/2022\/01\/12005157\/Picture811-300x125.png\" alt=\"A small flowchart. At the top, there is a box that reads &quot;Available Test Subjects\/Experimental Units. As similar as possible.&quot; There are two arrows leading to different boxes, both labeled &quot;Randomize.&quot; One of the boxes reads &quot;Control Group - Not Manipulated,&quot; while the other reads &quot;Experimental Group - Manipulated Design Factor.&quot;\" width=\"943\" height=\"392\" \/>\r\n\r\nIt is important to remember that the only difference between the experimental and control groups is the researcher\u2019s manipulation of the factor of interest.\r\n<div class=\"textbox exercises\">\r\n<h3>example<\/h3>\r\nComplete the sentence by filling in the blank.\r\n\r\nThe _______________ is not manipulated, while the _________________ receives the researcher's treatment.\r\n\r\n[reveal-answer q=\"207111\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"207111\"]\r\n\r\nThe <span style=\"text-decoration: underline;\">control group<\/span> is not manipulated, while the <span style=\"text-decoration: underline;\">experimental group<\/span> receives the researcher's treatment.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\nNow you try answering Question 3 to identify the experimental and control groups in the simplified experiment given above.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>question 3<\/h3>\r\nIn the previous simplified experiment:\r\n\r\nPart A: Which group is the experimental group?\r\n<ol start=\"6\">\r\n \t<li>a) 1,000 fish eggs in water with a pH of 6.5<\/li>\r\n \t<li>b) 1,000 fish eggs in water with a pH of 4.5<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"522756\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"522756\"]Which group has the unusual pH?[\/hidden-answer]\r\n\r\n&nbsp;\r\n\r\nPart B: Which group is the control group?\r\n<ol start=\"6\">\r\n \t<li>a) 1,000 fish eggs in water with a pH of 6.5<\/li>\r\n \t<li>b) 1,000 fish eggs in water with a pH of 4.5<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"244176\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"244176\"]Which group has the healthy pH?[\/hidden-answer]\r\n\r\n<\/div>\r\n<h3>\u00a0Random Assignment<\/h3>\r\nTo ensure that there are no unexpected differences between the experimental and control groups, good experimental design uses <strong>random assignment<\/strong> to determine which participants are in each group. This helps to minimize the impact of other variables that the researcher has no control over. Do not confuse this with random sampling! (In fact, most experiments do not use random sampling to find their sample.)\r\n\r\nIn our previous fish experiment, random assignment means that no matter how the 2,000 fish eggs were obtained, the ecologist would use some system of randomization to divide the eggs into two equal groups. For example, the researcher can use a random number generator to select 1,000 fish to be in the control group and then assign the remaining 1,000 fish to the experimental group. This would help to minimize the impact of other potential variables, such as the genetics and health of individual eggs.\r\n<div class=\"textbox tryit\">\r\n<h3>Video Placement<\/h3>\r\n<span style=\"background-color: #e6daf7;\">[Perspective Video with a worked example: a 3-instructor video that explains the difference between random sampling and random assignment. These types of similar terms present a significant challenge to students who don't yet have a mental landscape of statistics. This explanation should be followed by one or two examples in the style of Question 4]<\/span>\r\n\r\n<\/div>\r\nNow it's your turn to try identifying random assignment using statistical descriptions.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>question 4<\/h3>\r\n<span style=\"font-size: 1rem; text-align: initial;\">Identify the scenario(s) below that describe(s) random assignment (not random sampling). There may be more than one correct answer.<\/span>\r\n<ol>\r\n \t<li>a) A political pollster uses an electronic database to randomly generate a list of telephone numbers to call with questions about an upcoming election.<\/li>\r\n \t<li>b) A researcher uses a random number generator to determine which patients will receive an experimental medication and which patients will receive standard treatment.<\/li>\r\n \t<li>c) A researcher flips a coin to decide whether to assign a new participant to the experimental or control group.<\/li>\r\n \t<li>d) A professor uses a random number generator to decide which students to contact for a course evaluation.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"220252\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"220252\"]Remember that random assignment is how participants are assigned to the experimental or control group, not how they are selected for participation in the study.[\/hidden-answer]\r\n\r\n<\/div>\r\n<h3>\u00a0Replication<\/h3>\r\nThe final component of experimental design that we will explore is replication.\u00a0In addition to random assignment, <strong>replication<\/strong> helps ensure that the results of an experiment are truly caused by the change in the factor of interest and not by other hidden factors or natural variation in data. A good experiment always achieves replication by including large numbers of participants, but replication can also be achieved by repeating the entire experiment with new groups of participants. As you will learn in future lessons, certain statistical analyses can only be performed if the sample meets a minimum size requirement.\r\n\r\nSee the example below for a summary of replication, then answer Question 5.\r\n<div class=\"textbox exercises\">\r\n<h3>example<\/h3>\r\nFill in the blanks to complete these sentences.\r\n\r\nReplication helps ensure that the results of an experiment are truly caused by ________________________ and not by ____________________________. A good experiment can achieve replication by ________________________ or by _______________________________.\r\n\r\n[reveal-answer q=\"185602\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"185602\"]\r\n\r\nReplication helps ensure that the results of an experiment are truly caused by <span style=\"text-decoration: underline;\">the change in the factor of interest<\/span> and not by <span style=\"text-decoration: underline;\">other hidden factors or natural variation in data<\/span>. A good experiment can achieve replication by <span style=\"text-decoration: underline;\">including large numbers of participants<\/span> or by\u00a0<span style=\"text-decoration: underline;\">repeating the entire experiment with new groups of participants.<\/span>\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\nNow you try it. Use the information you found above to help you answer Question 5.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>question 5<\/h3>\r\nWhich form of replication is demonstrated in the previous fish experiment?\r\n<ol>\r\n \t<li>a) Many participants included in one experiment<\/li>\r\n \t<li>b) The experiment repeated with different participants<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"34644\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"34644\"]How many times did the ecologist collect data?[\/hidden-answer]\r\n\r\n<\/div>\r\n<h3>Looking ahead<\/h3>\r\nIn the upcoming activity, you will design an experiment\u00a0to study the health of coral reefs in our oceans. Use the National Ocean Service website provided here to learn some basic facts about coral, then record your responses to Question 6. Make sure to have your responses available during the activity.\r\n\r\nRead the article on this webpage (make sure to read the \"Did you know?\" section!) then answer Question 6.\r\n\r\n<a href=\"https:\/\/oceanservice.noaa.gov\/facts\/coral.html\">https:\/\/oceanservice.noaa.gov\/facts\/coral.html<\/a>.\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Question 6<\/h3>\r\nAnswer the following questions. Don't forget to have your answers available during the upcoming activity!\r\n\r\n&nbsp;\r\n\r\nPart A: Is coral a plant? An animal? Both?\r\n\r\n&nbsp;\r\n\r\nPart B: What are some factors that impact the health of coral reefs?\r\n\r\n&nbsp;\r\n\r\nPart C: What is coral bleaching?\r\n\r\n[reveal-answer q=\"635127\"]Hint[\/reveal-answer]\r\n[hidden-answer a=\"635127\"]Make sure to read the \u201cDid you know?\u201d section![\/hidden-answer]\r\n\r\n<\/div>\r\n<h2>Summary<\/h2>\r\nIn this\u00a0<em>What to Know\u00a0<\/em>page,\u00a0you learned several key components of experimental design. Let\u2019s summarize where each of these terms showed up on the questions.\r\n<ul>\r\n \t<li>In Question 2, Parts A and B, you identified the factor of interest and response factor in an experiment.<\/li>\r\n \t<li>In Question 2, Part C, you identified the nuisance factors in an experiment.<\/li>\r\n \t<li>In Question 3, Parts A and B, you identified the experimental and control groups in an experiment.<\/li>\r\n \t<li>In Question 4, you recognized random assignment.<\/li>\r\n \t<li>In Question 5, you identified which of two methods of replication was used in a study.<\/li>\r\n \t<li>In Question 6, you\u00a0prepared for the upcoming activity. Don't forget to have your answer ready when you begin the activity!<\/li>\r\n<\/ul>\r\nThere was quite a lot of information in this section. Feel free to return to it as needed in the future to refresh the definitions and your understanding. If you feel comfortable with these ideas, it\u2019s time to practice them in the upcoming activity.","rendered":"<div class=\"textbox learning-objectives\">\n<h3>learning GOALS<\/h3>\n<p>At the end of this page, you should feel comfortable performing these skills:<\/p>\n<ul>\n<li>Identify the factor of interest and response factor in an experiment.<\/li>\n<li>Identify the nuisance factors in an experiment.<\/li>\n<li>Identify the experimental and control groups in an experiment.<\/li>\n<li>Recognize random assignment.<\/li>\n<li>Identify which of two methods of replication was used in an experiment.<\/li>\n<\/ul>\n<\/div>\n<p>Experimental design refers to the structure of an experiment (a specific type of research method). How can the experiment be conducted efficiently, effectively, and responsibly, to return sound results? Researchers must carefully consider several key components of experimental design before any work is done to collect data.<\/p>\n<p>In the upcoming activity, you will need to identify the key components of experimental design. We&#8217;ll take them one by one in the following questions.<\/p>\n<h2>Experimental Design<\/h2>\n<p>An experimental study, or experiment, is a specific method of research that is especially useful for determining cause and effect. Typically, a basic experiment design includes a treatment imposed by the researcher, a comparison between one group that receives the treatment and another group that does not, and random assignment of participants into each group. We\u2019ll explore each of these concepts in more detail below.<\/p>\n<p>To help you understand the key components of experimental design, consider this simplified experiment:<\/p>\n<p><span style=\"background-color: #ffff99;\">[insert an image of a lake? fish eggs? pH strips?]<\/span><\/p>\n<p><em>An ecologist wants to know if acid rain affects the rate of reproduction for fish in a local lake. The ecologist incubates 1,000 fish eggs in healthy lake water (pH = 6.5) and another 1,000 fish eggs in acidic water (pH = 4.5). The eggs have been randomly assigned to either the healthy lake water group or the acidic water group. The water temperature, amount of dissolved oxygen, and amount and timing of light were kept at optimal levels for both groups. After 14 days, the ecologist counted how many eggs from each group had hatched.<\/em><\/p>\n<p>Each of the questions below will ask about aspects of the design present in this experiment.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>question 1<\/h3>\n<p>A good experiment always starts with a good research question. For an experiment, the research question is usually about whether one thing causes another. Fill in the blanks below to summarize the ecologist\u2019s research question.<\/p>\n<p>\u201cDoes ______________________ cause ________________________?\u201d<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q727621\">Hint<\/span><\/p>\n<div id=\"q727621\" class=\"hidden-answer\" style=\"display: none\">What does the ecologist want to know? What is the specific cause and effect the ecologist is investigating?<\/div>\n<\/div>\n<\/div>\n<h3>Factors<\/h3>\n<p>In an experimental study, the <strong>factor of interest<\/strong> (also known as the <strong>explanatory variable<\/strong> or independent variable) is the factor that the researcher purposely changes or manipulates to see if it impacts a specific outcome. The <strong>treatments<\/strong> are the different levels of the factor of interest (or explanatory variable) you are changing (e.g., no vaccine vs. vaccine).<\/p>\n<p>The <strong>response variable<\/strong> (also known as the <strong>dependent variable<\/strong>) is an objective measure of the research question that is measured at the end of an experiment and compared across the different levels of the factor of interest (or explanatory variable).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1391\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5738\/2022\/01\/14234115\/Picture192-300x67.jpg\" alt=\"A small flowchart. The first box says &quot;Factor of Interest \/ Explanatory Variable.&quot; There is an arrow beside it labeled &quot;affects&quot; going to the second box, labeled &quot;Response Variable.&quot;\" width=\"1294\" height=\"289\" \/><\/p>\n<p>The <strong>nuisance factors<\/strong> are factors that are kept the same across all levels of the factor or are explicitly controlled in the experimental design. These factors are not of interest in the study but may affect a change in the response variable.<\/p>\n<div class=\"textbox tryit\">\n<h3>Video Placement<\/h3>\n<p><span style=\"background-color: #e6daf7;\">[A video briefly describing factor of interest, treatment, response variable, and nuisance factors. This should be no more than a minute long. ]<\/span><\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Example<\/h3>\n<p>Summarize the terminology surrounding factors by answering the questions below.<\/p>\n<ol>\n<li>The factor of interest is also known as the _________________. Fill in the blank.<\/li>\n<li>The response variable is also known as the ________________. Fill in the blank.<\/li>\n<li>What does the researcher purposely change or manipulate to see if it impacts a specific outcome? Choose all that apply\n<ol>\n<li>a) experimental factor<\/li>\n<li>b) explanatory variable<\/li>\n<li>c) response factor<\/li>\n<li>d) factor of interest<\/li>\n<\/ol>\n<\/li>\n<li>What are treatments in an experiment?\n<ol>\n<li>a) medicine applied to one set of individuals but not the other<\/li>\n<li>b)\u00a0the different levels of the factor of interest (or explanatory variable) you are changing<\/li>\n<\/ol>\n<\/li>\n<li>What are nuisance factors in an experiment?\n<ol>\n<li>a) types of observational units that are particularly bothersome such as loud talkers<\/li>\n<li>b) types of factors that researchers are unable to account for in an experiment<\/li>\n<li>c)\u00a0factors that are kept the same across all levels of the factor or are explicitly controlled in the experimental design<\/li>\n<\/ol>\n<\/li>\n<li>What is measured at the end of an experiment and compared across the different levels of the factor of interest?<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q54865\">Show Answer<\/span><\/p>\n<div id=\"q54865\" class=\"hidden-answer\" style=\"display: none\">1. explanatory variable; 2. dependent variable; 3. b and d; 4. b; 5. c; 6. the response variable<\/div>\n<\/div>\n<\/div>\n<p>Now you try. Use the definitions given above to answer Question 2. Remember to view the feedback for your answers to assess your understanding.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>question 2<\/h3>\n<p>Identify the different parts of the experimental design in the previous simplified experiment.<\/p>\n<p>Part A: What is the factor of interest?<\/p>\n<ol>\n<li>a) pH level<\/li>\n<li>b) Temperature<\/li>\n<li>c) Oxygen level<\/li>\n<li>d) Amount of light<\/li>\n<li>e) Timing of light<\/li>\n<li>f) Incubation duration<\/li>\n<li>g) Number of eggs hatched<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q344691\">Hint<\/span><\/p>\n<div id=\"q344691\" class=\"hidden-answer\" style=\"display: none\">Which factor did the ecologist purposely change?<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p>Part B: What is the response variable?<\/p>\n<ol>\n<li>a) pH<\/li>\n<li>b) Temperature<\/li>\n<li>c) Oxygen level<\/li>\n<li>d) Amount of light<\/li>\n<li>e) Timing of light<\/li>\n<li>f)\u00a0 Incubation duration<\/li>\n<li>g) Number of eggs hatched<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q821608\">Hint<\/span><\/p>\n<div id=\"q821608\" class=\"hidden-answer\" style=\"display: none\">Which factor did the ecologist measure at the end of the study?<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p>Part C: What are the nuisance factors in the previous experiment? There may be more than one correct answer.<\/p>\n<ol>\n<li>a) pH<\/li>\n<li>b) Temperature<\/li>\n<li>c) Oxygen level<\/li>\n<li>d) Amount of light<\/li>\n<li>e) Timing of light<\/li>\n<li>f) Incubation duration<\/li>\n<li>g) Number of eggs hatched<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q861184\">Hint<\/span><\/p>\n<div id=\"q861184\" class=\"hidden-answer\" style=\"display: none\">Which factors did the ecologist keep the same for both groups?<\/div>\n<\/div>\n<\/div>\n<h3>Controls<\/h3>\n<p>An important aspect of all experiments is a comparison between one or more groups or <strong>levels<\/strong> of the factor of interest, called <strong>treatments<\/strong>. In a simple experimental design, one group receives the researcher\u2019s treatment and the other group(s) does not. The group that receives the treatment is commonly called the experimental group. The group that does not receive the treatment is usually called the control group. The control group is usually kept under conditions that are considered typical or common for a given situation.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-1112\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/5738\/2022\/01\/12005157\/Picture811-300x125.png\" alt=\"A small flowchart. At the top, there is a box that reads &quot;Available Test Subjects\/Experimental Units. As similar as possible.&quot; There are two arrows leading to different boxes, both labeled &quot;Randomize.&quot; One of the boxes reads &quot;Control Group - Not Manipulated,&quot; while the other reads &quot;Experimental Group - Manipulated Design Factor.&quot;\" width=\"943\" height=\"392\" \/><\/p>\n<p>It is important to remember that the only difference between the experimental and control groups is the researcher\u2019s manipulation of the factor of interest.<\/p>\n<div class=\"textbox exercises\">\n<h3>example<\/h3>\n<p>Complete the sentence by filling in the blank.<\/p>\n<p>The _______________ is not manipulated, while the _________________ receives the researcher&#8217;s treatment.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q207111\">Show Answer<\/span><\/p>\n<div id=\"q207111\" class=\"hidden-answer\" style=\"display: none\">\n<p>The <span style=\"text-decoration: underline;\">control group<\/span> is not manipulated, while the <span style=\"text-decoration: underline;\">experimental group<\/span> receives the researcher&#8217;s treatment.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<p>Now you try answering Question 3 to identify the experimental and control groups in the simplified experiment given above.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>question 3<\/h3>\n<p>In the previous simplified experiment:<\/p>\n<p>Part A: Which group is the experimental group?<\/p>\n<ol start=\"6\">\n<li>a) 1,000 fish eggs in water with a pH of 6.5<\/li>\n<li>b) 1,000 fish eggs in water with a pH of 4.5<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q522756\">Hint<\/span><\/p>\n<div id=\"q522756\" class=\"hidden-answer\" style=\"display: none\">Which group has the unusual pH?<\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p>Part B: Which group is the control group?<\/p>\n<ol start=\"6\">\n<li>a) 1,000 fish eggs in water with a pH of 6.5<\/li>\n<li>b) 1,000 fish eggs in water with a pH of 4.5<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q244176\">Hint<\/span><\/p>\n<div id=\"q244176\" class=\"hidden-answer\" style=\"display: none\">Which group has the healthy pH?<\/div>\n<\/div>\n<\/div>\n<h3>\u00a0Random Assignment<\/h3>\n<p>To ensure that there are no unexpected differences between the experimental and control groups, good experimental design uses <strong>random assignment<\/strong> to determine which participants are in each group. This helps to minimize the impact of other variables that the researcher has no control over. Do not confuse this with random sampling! (In fact, most experiments do not use random sampling to find their sample.)<\/p>\n<p>In our previous fish experiment, random assignment means that no matter how the 2,000 fish eggs were obtained, the ecologist would use some system of randomization to divide the eggs into two equal groups. For example, the researcher can use a random number generator to select 1,000 fish to be in the control group and then assign the remaining 1,000 fish to the experimental group. This would help to minimize the impact of other potential variables, such as the genetics and health of individual eggs.<\/p>\n<div class=\"textbox tryit\">\n<h3>Video Placement<\/h3>\n<p><span style=\"background-color: #e6daf7;\">[Perspective Video with a worked example: a 3-instructor video that explains the difference between random sampling and random assignment. These types of similar terms present a significant challenge to students who don&#8217;t yet have a mental landscape of statistics. This explanation should be followed by one or two examples in the style of Question 4]<\/span><\/p>\n<\/div>\n<p>Now it&#8217;s your turn to try identifying random assignment using statistical descriptions.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>question 4<\/h3>\n<p><span style=\"font-size: 1rem; text-align: initial;\">Identify the scenario(s) below that describe(s) random assignment (not random sampling). There may be more than one correct answer.<\/span><\/p>\n<ol>\n<li>a) A political pollster uses an electronic database to randomly generate a list of telephone numbers to call with questions about an upcoming election.<\/li>\n<li>b) A researcher uses a random number generator to determine which patients will receive an experimental medication and which patients will receive standard treatment.<\/li>\n<li>c) A researcher flips a coin to decide whether to assign a new participant to the experimental or control group.<\/li>\n<li>d) A professor uses a random number generator to decide which students to contact for a course evaluation.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q220252\">Hint<\/span><\/p>\n<div id=\"q220252\" class=\"hidden-answer\" style=\"display: none\">Remember that random assignment is how participants are assigned to the experimental or control group, not how they are selected for participation in the study.<\/div>\n<\/div>\n<\/div>\n<h3>\u00a0Replication<\/h3>\n<p>The final component of experimental design that we will explore is replication.\u00a0In addition to random assignment, <strong>replication<\/strong> helps ensure that the results of an experiment are truly caused by the change in the factor of interest and not by other hidden factors or natural variation in data. A good experiment always achieves replication by including large numbers of participants, but replication can also be achieved by repeating the entire experiment with new groups of participants. As you will learn in future lessons, certain statistical analyses can only be performed if the sample meets a minimum size requirement.<\/p>\n<p>See the example below for a summary of replication, then answer Question 5.<\/p>\n<div class=\"textbox exercises\">\n<h3>example<\/h3>\n<p>Fill in the blanks to complete these sentences.<\/p>\n<p>Replication helps ensure that the results of an experiment are truly caused by ________________________ and not by ____________________________. A good experiment can achieve replication by ________________________ or by _______________________________.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q185602\">Show Answer<\/span><\/p>\n<div id=\"q185602\" class=\"hidden-answer\" style=\"display: none\">\n<p>Replication helps ensure that the results of an experiment are truly caused by <span style=\"text-decoration: underline;\">the change in the factor of interest<\/span> and not by <span style=\"text-decoration: underline;\">other hidden factors or natural variation in data<\/span>. A good experiment can achieve replication by <span style=\"text-decoration: underline;\">including large numbers of participants<\/span> or by\u00a0<span style=\"text-decoration: underline;\">repeating the entire experiment with new groups of participants.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<p>Now you try it. Use the information you found above to help you answer Question 5.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>question 5<\/h3>\n<p>Which form of replication is demonstrated in the previous fish experiment?<\/p>\n<ol>\n<li>a) Many participants included in one experiment<\/li>\n<li>b) The experiment repeated with different participants<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q34644\">Hint<\/span><\/p>\n<div id=\"q34644\" class=\"hidden-answer\" style=\"display: none\">How many times did the ecologist collect data?<\/div>\n<\/div>\n<\/div>\n<h3>Looking ahead<\/h3>\n<p>In the upcoming activity, you will design an experiment\u00a0to study the health of coral reefs in our oceans. Use the National Ocean Service website provided here to learn some basic facts about coral, then record your responses to Question 6. Make sure to have your responses available during the activity.<\/p>\n<p>Read the article on this webpage (make sure to read the &#8220;Did you know?&#8221; section!) then answer Question 6.<\/p>\n<p><a href=\"https:\/\/oceanservice.noaa.gov\/facts\/coral.html\">https:\/\/oceanservice.noaa.gov\/facts\/coral.html<\/a>.<\/p>\n<div class=\"textbox key-takeaways\">\n<h3>Question 6<\/h3>\n<p>Answer the following questions. Don&#8217;t forget to have your answers available during the upcoming activity!<\/p>\n<p>&nbsp;<\/p>\n<p>Part A: Is coral a plant? An animal? Both?<\/p>\n<p>&nbsp;<\/p>\n<p>Part B: What are some factors that impact the health of coral reefs?<\/p>\n<p>&nbsp;<\/p>\n<p>Part C: What is coral bleaching?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q635127\">Hint<\/span><\/p>\n<div id=\"q635127\" class=\"hidden-answer\" style=\"display: none\">Make sure to read the \u201cDid you know?\u201d section!<\/div>\n<\/div>\n<\/div>\n<h2>Summary<\/h2>\n<p>In this\u00a0<em>What to Know\u00a0<\/em>page,\u00a0you learned several key components of experimental design. Let\u2019s summarize where each of these terms showed up on the questions.<\/p>\n<ul>\n<li>In Question 2, Parts A and B, you identified the factor of interest and response factor in an experiment.<\/li>\n<li>In Question 2, Part C, you identified the nuisance factors in an experiment.<\/li>\n<li>In Question 3, Parts A and B, you identified the experimental and control groups in an experiment.<\/li>\n<li>In Question 4, you recognized random assignment.<\/li>\n<li>In Question 5, you identified which of two methods of replication was used in a study.<\/li>\n<li>In Question 6, you\u00a0prepared for the upcoming activity. Don&#8217;t forget to have your answer ready when you begin the activity!<\/li>\n<\/ul>\n<p>There was quite a lot of information in this section. Feel free to return to it as needed in the future to refresh the definitions and your understanding. If you feel comfortable with these ideas, it\u2019s time to practice them in the upcoming activity.<\/p>\n","protected":false},"author":493460,"menu_order":48,"template":"","meta":{"_candela_citation":"[]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-3518","chapter","type-chapter","status-publish","hentry"],"part":3418,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapters\/3518","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/wp\/v2\/users\/493460"}],"version-history":[{"count":16,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapters\/3518\/revisions"}],"predecessor-version":[{"id":4307,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapters\/3518\/revisions\/4307"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/parts\/3418"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapters\/3518\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/wp\/v2\/media?parent=3518"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/pressbooks\/v2\/chapter-type?post=3518"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/wp\/v2\/contributor?post=3518"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/lumen-danacenter-statsmockup\/wp-json\/wp\/v2\/license?post=3518"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}