How to Determine if the 10% Rule is Satisfied When Sampling is Done Without Replacement
Step 1: Identify the population size, {eq}N{/eq}, and calculate 10% of the population size, {eq}0.1N{/eq}.
Step 2: Identify the sample size, {eq}n{/eq}.
Step 3: Compare the sample size to 10% of the population size.
- If {eq}n\leq 0.1 N{/eq} then the 10% rule is satisfied.
- If {eq}n>0.1 N{/eq} then the 10% rule is not satisfied.
What is the 10% Rule?
10% Rule: The 10% rule is a statistical rule that allows Bernoulli trials to be treated as independent, even if they are taken without replacement. A Bernoulli trial is an experiment with two possible outcomes, success or failure. Sampling without replacement results in trials that are not independent, but the 10% rule states that if the sample size is less than or equal to 10% of the population size, then the trials can be treated as if they are independent.
We will use these steps, definitions, and equations to determine if the 10% rule is satisfied when sampling is done without replacement in the following two examples.
Examples of Determining if the 10% Rule is Satisfied
Example 1
A researcher wants to determine the proportion of adults in a particular city who prefer dogs over cats. He plans to randomly select, without replacement, 1,000 adults to survey out of the population of 35,000 adults. Does his sampling design satisfy the 10% rule?
Step 1: Identify the population size, {eq}N{/eq}, and calculate 10% of the population size, {eq}0.1 N{/eq}.
The population size is the total number of adults in the city, {eq}N = 35,000{/eq}. Then, 10% of this population size is {eq}0.1N = 0.1(35,000) = 3,500{/eq} adults.
Step 2: Identify the sample size, {eq}n{/eq}.
The sample size is {eq}n = 1,000{/eq}.
Step 3: Compare the sample size to 10% of the population size.
- If {eq}n\leq 0.1N{/eq} then the 10% rule is satisfied.
- If {eq}n>0.1N{/eq} then the 10% rule is not satisfied.
Since {eq}1,000 < 3,500{/eq}, the sample consists of less than 10% of the population size. Therefore, the 10% rule is satisfied.
Example 2
A cafeteria worker wants to determine the proportion of high school students who prefer chocolate milk over white milk with their lunch. She plans to randomly select and survey 100 students, without replacement, from the 500 students at the high school. Does this sampling plan satisfy the 10% rule?
Step 1: Identify the population size, {eq}N{/eq}, and calculate 10% of the population size, {eq}0.1 N{/eq}.
The population size is {eq}N = 500{/eq}. 10% of this population size is {eq}0.1 N = 0.1(500) = 50{/eq} students.
Step 2: Identify the sample size, {eq}n{/eq}.
The sample size is {eq}n = 100{/eq}.
Step 3: Compare the sample size to 10% of the population size.
- If {eq}n\leq 0.1 N{/eq} then the 10% rule is satisfied.
- If {eq}n>0.1 N{/eq} then the 10% rule is not satisfied.
Since {eq}100 > 50{/eq}, the sample consists of more than 10% of the population size. Therefore, the 10% rule is not satisfied.