determining sample size

Determining Sample Size - 07-11-2013 by Melissa Moran - Statistics Solutions - Deter...

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Determining Sample Size - 07-11-2013 by Melissa Moran - Statistics Solutions -

Determining Sample Size Getting the most out of surveys requires a few prerequisites. One prerequisite is understanding and determining sample size. It’s funny, our clients typically think they either have too many participants or too few participants, but rarely ask how one calculates the appropriate sample size. The sample size requirement for surveys is important issue in at least two ways: the generalizability of the findings and appropriate statistical power. Generalizability. Generally speaking, you can only generalize to a population from which you sampled. For example, if you survey clients in the Northwest, you may not be able to necessarily generalize to those in the Southeast. Further, if you seek to generalize to different regions you need to stratify your sample so all areas are represented. Once you’ve determined who to sample and where to sample, you can go to Statistics Solutions Sample Size Calculator to determine how many participants you require. For example, if the population you are examining is 1,000,000, you would need to systemically sample roughly 10,500 individuals. Statistical Power. The other type of sample size is about achieving statistical power. Statistical power is the ability to state that you how a chance of finding differences or relationship among variable. Typical statistical power is .80, meaning that given a particular sample size, you have an 80% chance of finding differences or relationships if differences or relationships actually exist in your population. For example, if you wanted to examine whether there is a relationship between age and the purchase amount, a correlation was be the correct statistical test. Given that statistical test, 85 participants would be required. Timing. The time to inquire able the sample size is before you begin your study. Administering your survey, conducting analyses, then wondering if you had enough participants is not the way to go here. Get a sample size consultation before you begin collecting data, understand what that sample size justification serves, and you’re on the road to a successful survey.


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