Experimental Design: Learn It 2

Controls

An important aspect of all experiments is a comparison between one or more groups or levels of the factor of interest, called treatments. In a simple experimental design, one group receives the researcher’s 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.

A small flowchart. At the top, there is a box that reads "Available Test Subjects/Experimental Units. As similar as possible." There are two arrows leading to different boxes, both labeled "Randomize." One of the boxes reads "Control Group - Not Manipulated," while the other reads "Experimental Group - Manipulated Design Factor."

It is important to remember that the only difference between the experimental and control groups is the researcher’s manipulation of the factor of interest.

example

Complete the sentence by filling in the blank.

The _______________ is not manipulated, while the _________________ receives the researcher’s treatment.

Now you try answering Question 3 to identify the experimental and control groups in the simplified experiment given above.

question 3

In the previous simplified experiment:

Part A: Which group is the experimental group?

  1. a) 1,000 fish eggs in water with a pH of 6.5
  2. b) 1,000 fish eggs in water with a pH of 4.5

 

Part B: Which group is the control group?

  1. a) 1,000 fish eggs in water with a pH of 6.5
  2. b) 1,000 fish eggs in water with a pH of 4.5