Question 1

Why is 385 so common in survey guides?

Accepted Answer

It is the result for 95% confidence, ±5% and p = 50%, the most frequently used default.

Question 2

Does a population of 1 million need a larger sample than 100,000?

Accepted Answer

Barely. Once the population is much larger than the sample, size hardly matters; precision depends mainly on n.

Question 3

Should I use a different p than 50%?

Accepted Answer

If a reliable earlier study suggests, say, 20%, using it gives a smaller n (246 at 95% and ±5%). Use 50% if unsure.

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