Survey Sample Size. MKTG 3342 Fall 2008 Professor Edward Fox. Sample Size Determination. Convenience – Say … about 100. Rule of Thumb - At least 30 per each subgroup (e.g., males/females) that will be analyzed.
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Professor Edward Fox
Typical Sample Sizes for Studies of
Human and Institutional Populations
People or Households
None or few
There are statistical formulas for computing sample sizes. These consider three aspects:
Precision: Percent of sampling error deemed acceptable by the researcher
Confidence: How confident is the researcher that the true average value lies in the interval [lower, upper] estimated
Variance: Dispersion of the true value across the population
There are many sample size calculators on the web.
Two such websites are:
The formula on the first website is for estimating proportions. Use 95% and 99% confidence level, and confidence interval (allowable error) to be 2% to 10%. Use any population size such as 100, 1000, 10,000. See what happens to sample size as you vary the parameters.
For Mail Surveys:
Estimating the number of surveys required to achieve given sample size:
Surveys Required =
n = required sample size
U= estimated proportion “not deliverable”
RR = estimated response rate (proportion)
For Telephone Surveys:
#Completed + #Refusals + #No Answers
Estimating the number of calls required to achieve given sample size:
Total Calls =
[(1-NE) (1-R) (1-NA)]
where: n = required sample size
NE= estimated proportion of non-eligibles
R = estimated proportion of refusals
NA = estimated proportion of no answers