Sampling question #2: How do I determine sample size?

Many students wonder about their sample size. How large should it be? Some of the decision is based on practical aspects. What population do you have access to? How much time and money are you willing or able to spend on sample acquisition. Here are some real world sampling suggestions to help you out!

*Ask experts what they would suggest for sample size.

*See what the literature recommends.

*Must have at least 10 per cell for statistical analysis.

*Rule of thumb- larger is better.

If you would like to get a feeling for the size of samples that represent entire populations, please refer to Krejcie (1970). The chart below suggests the great benefit that randomly-selected samples afford. (Population size is noted by uppercase ā€œNā€ and sample size by lower case ā€œnā€.)

Random Sample Sizes (n) Required for Population (N) Representation

Population Size (N) ------ Sample Size(n)

50 ------------------ 44

100 ----------------- 80

500 ----------------- 217

1,000 ---------------- 278

1,500 ---------------- 306

3,000 ---------------- 341

5,000 ---------------- 357

10,000 --------------- 375

50,000 --------------- 381

100,000 -------------- 384

Source: Krejcie, R.V. & Morgan, D.W. (1970) Determining sample size for research activities. Educational and Psychological Measurements, 30, 607-610.

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