{"id":5168,"date":"2016-07-20T21:04:55","date_gmt":"2016-07-20T21:04:55","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microeconomics\/?post_type=chapter&p=5168"},"modified":"2016-07-20T21:04:55","modified_gmt":"2016-07-20T21:04:55","slug":"reading-calculating-percentage-changes-and-growth-rates","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/atd-herkimer-microeconomics\/chapter\/reading-calculating-percentage-changes-and-growth-rates\/","title":{"raw":"Reading: Calculating Percentage Changes and Growth Rates","rendered":"Reading: Calculating Percentage Changes and Growth Rates"},"content":{"raw":"\"Photo<\/a>\n\nIn order to measure elasticity, we need to calculate percentage change, also known as a growth<\/strong> rate<\/strong>.\u00a0The formula for computing a growth rate is straightforward:\n

[latex]\\text{Percentage change}=\\frac{\\text{Change in quantity}}{\\text{Quantity}}[\/latex]<\/p>\nSuppose that a\u00a0job pays $10 per hour. At some point, the individual doing the job is\u00a0given\u00a0a $2-per-hour raise. The percentage change (or growth rate) in pay is [latex]\\frac{\\$2}{\\$10}=0.20\\text{ or }20\\%[\/latex].\n\nNow, recall that we defined elasticity as the percentage change in something divided by the percentage change in something else. Let\u2019s take the price elasticity of demand as an example. The price elasticity of demand is defined as the percentage change in quantity demanded divided by the percentage change in price:\n

[latex]\\text{Price elasticity of demand}=\\frac{\\text{Percentage change in quantity demanded}}{\\text{Percentage change in price}}[\/latex]<\/p>\nThere are two general methods\u00a0for calculating elasticities: the point elasticity approach and the midpoint (or arc) elasticity approach. Elasticity looks at the percentage change in quantity demanded divided by the percentage change in price, but which quantity and which price should be the denominator in the percentage calculation? The point approach uses the initial price and initial quantity to measure percent change. This makes the math easier, but the more accurate approach is the midpoint approach, which uses the average price and average quantity over the price and quantity change. (These are the price and quantity halfway between the initial point and the final point.\u00a0\u00a0 Let\u2019s compare the two approaches.\n\nSuppose the quantity demanded of a product\u00a0was 100\u00a0at one point on the demand curve, and then it moved to\u00a0103 at another point. The growth rate, or percentage change in quantity demanded, would be the change in quantity demanded [latex]{(103-100)}[\/latex] divided by the average\u00a0of the two quantities demanded\u00a0[latex]\\frac{(103+100)}{2}[\/latex]. In other words,\u00a0the growth rate:\n

[latex]=\\frac{103-100}{(103+100)\/2}\\\\=\\frac{3}{101.5}\\\\=0.0296\\\\=2.96\\%\\text{growth}[\/latex]<\/p>\nNote that if we used the point approach, the calculation would be:\n

[latex]\\frac{(103\u2013100)}{100}=3\\%\\text{ growth}[\/latex]<\/p>\nThis produces\u00a0nearly the same result as the slightly more complicated midpoint method (3% vs. 2.96%). If you need a rough approximation, use the point\u00a0method. If you need accuracy, use the midpoint\u00a0method.\n\nIn this module you will often be asked to calculate the percentage change<\/em> in the quantity, but keep in mind that this is the growth rate. That way as you work\u00a0through the course and find a need to calculate the growth rates beyond elasticity, you will be well prepared.","rendered":"

\"Photo<\/a><\/p>\n

In order to measure elasticity, we need to calculate percentage change, also known as a growth<\/strong> rate<\/strong>.\u00a0The formula for computing a growth rate is straightforward:<\/p>\n

[latex]\\text{Percentage change}=\\frac{\\text{Change in quantity}}{\\text{Quantity}}[\/latex]<\/p>\n

Suppose that a\u00a0job pays $10 per hour. At some point, the individual doing the job is\u00a0given\u00a0a $2-per-hour raise. The percentage change (or growth rate) in pay is [latex]\\frac{\\$2}{\\$10}=0.20\\text{ or }20\\%[\/latex].<\/p>\n

Now, recall that we defined elasticity as the percentage change in something divided by the percentage change in something else. Let\u2019s take the price elasticity of demand as an example. The price elasticity of demand is defined as the percentage change in quantity demanded divided by the percentage change in price:<\/p>\n

[latex]\\text{Price elasticity of demand}=\\frac{\\text{Percentage change in quantity demanded}}{\\text{Percentage change in price}}[\/latex]<\/p>\n

There are two general methods\u00a0for calculating elasticities: the point elasticity approach and the midpoint (or arc) elasticity approach. Elasticity looks at the percentage change in quantity demanded divided by the percentage change in price, but which quantity and which price should be the denominator in the percentage calculation? The point approach uses the initial price and initial quantity to measure percent change. This makes the math easier, but the more accurate approach is the midpoint approach, which uses the average price and average quantity over the price and quantity change. (These are the price and quantity halfway between the initial point and the final point.\u00a0\u00a0 Let\u2019s compare the two approaches.<\/p>\n

Suppose the quantity demanded of a product\u00a0was 100\u00a0at one point on the demand curve, and then it moved to\u00a0103 at another point. The growth rate, or percentage change in quantity demanded, would be the change in quantity demanded [latex]{(103-100)}[\/latex] divided by the average\u00a0of the two quantities demanded\u00a0[latex]\\frac{(103+100)}{2}[\/latex]. In other words,\u00a0the growth rate:<\/p>\n

[latex]=\\frac{103-100}{(103+100)\/2}\\\\=\\frac{3}{101.5}\\\\=0.0296\\\\=2.96\\%\\text{growth}[\/latex]<\/p>\n

Note that if we used the point approach, the calculation would be:<\/p>\n

[latex]\\frac{(103\u2013100)}{100}=3\\%\\text{ growth}[\/latex]<\/p>\n

This produces\u00a0nearly the same result as the slightly more complicated midpoint method (3% vs. 2.96%). If you need a rough approximation, use the point\u00a0method. If you need accuracy, use the midpoint\u00a0method.<\/p>\n

In this module you will often be asked to calculate the percentage change<\/em> in the quantity, but keep in mind that this is the growth rate. That way as you work\u00a0through the course and find a need to calculate the growth rates beyond elasticity, you will be well prepared.<\/p>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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