Is it possible to adapt a sample size of a previous study?
Thank You,
If the previous study is similar in standard deviation/diversity, and gave you reasonably accurate results, that sounds reasonable. If this is a quantitative data survey, then a previous survey may give you a good idea of standard deviation, and you can see what sample size is needed with it to obtain desired standard error, with attention to the sampling and inference methodology, which can include auxiliary/regressor data, and/or strata, etc. A pilot study might still be a good idea to confirm standard deviation(s), and explore designs.
Note that Cochran(1977), Sampling Techniques, 3rd ed, Wiley, says a pilot study or other information can help you make a good guess for standard deviation, when considering sample size. He has a chapter on sample size for continuous data and for proportions, using simple random sampling, and then other information on sample sizes for other designs in other chapters. There are many good sampling books besides that classic, but it is still a good one, though much more has been done with modeling since then.
Best wishes.
Obtain an effect size expected from the literature (MA, theory, etc.), then use select power and sensitivity levels in Power software to compute sample size needed to detect effect. I can suggest GPower free software for power calcs.
Hope this helps,
Matt
Before you can calculate a sample size, you need to determine a few things about the target population and the sample you need:
Population Size — How many total people fit your demographic?
Margin of Error (Confidence Interval) — No sample will be perfect, so you must decide how much error to allow.
Confidence Level — How confident do you want to be that the actual mean falls within your confidence interval? The most common confidence intervals are 90% confident, 95% confident, and 99% confident.
Standard of Deviation — How much variance do you expect in your responses? Since we haven’t actually administered our survey yet, the safe decision is to use .
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