StatCalc: Statistical Calculators
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Population Survey or Descriptive Study
The population survey calculates the sample size recommended for a survey given a set of parameters and the desired confidence level.
Guidelines
- The sample must be simple random or representative. A systematic sample (e.g., every fifth person on a list) is acceptable if the sample is representative. Choosing every other person from a list of couples would not give a representative sample because the sample population may include only males or only females.
- The survey questions must have a yes-no or other two-choice answer, leading to a proportion of the population (those answering yes) as the final result.
- For simple random sampling, the values for Design Effect and Clusters are 1 by definition.
Example
The following example investigates whether the true prevalence of the HIV antibody in a population is 10%. A random or systematic sample of the population is planned to estimate the prevalence. The desired sample size will be able to identify the prevalence of HIV with a +/- 3% margin of error. The application will show the sample size for several different confidence levels.
- From the Epi Info™ main page, select StatCalc.
- Select Population Survey. The Population Survey or Descriptive Study window opens.
- Enter the Population Size of 5,000.
- Enter the Expected Frequency of 10%.
- Enter the Acceptable Margin of Error of 6%.
- Enter the Design Effect of 1. This input designates the ratio of the variance of responses with clusters to the variance of a simple random sample.
- Enter the Clusters value of 1. This input designates the number of clusters in the population survey.
The results appear in the window.
![F1010-population-survey-descriptive-study StatCalc Sample Size and Power for a population survey or descriptive study.](/epiinfo/images/user-guide/stat-calc/F1010-population-survey-descriptive-study.png?_=54400)
The Total Sample column is the product of Cluster Size and Clusters. Each row designates how large of a sample size is required to achieve the necessary confidence level. Sample size determination is only a rough guide. Many other factors (e.g., cost, number of available subjects, rate of nonresponse, and the accuracy of answers and data transcription) must be considered in study design.