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Flashcards in Power and Sample Size Deck (12)
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How large a sample do I need

not too small bc if so it will be waste of money resources since you will not get anything out of that study

larger than necessary, study wastes resources

therefore must estimate power to determine sample size


precision analysis

estimate how large a sample is needed to produce a given level of precision at a fixed confidence level


Two types of statistical error

Type 1 error (alpha)
Type 2 error (beta)


Statistical power

1-beta; probability that the null hypothesis will be rejected when it is false


Under Neyman-Pearson, alpha is

set by investigator


Under Neyman-Pearson, beta

is estimated and will be determined by such characteristics as sample size, trait variance and effect size


Power analysis applies to

all major types of epi data:

1. dichotomous (binary)
2. multiple categories
3. continuous
4. time-to-event (in this case, power will be a function of the number of events)


as alpha decreases

so will the power. It will decrease

But beta increased


given in a fixed sample size:

if alpha increases, beta decreases

if alpha decreases, beta increases


without changing the null hypothesis, the only way to increase power while using a smaller alpha level is to increase sample size

increases precision

allows a smaller effect to be detected


Factors affecting statistical power

Z = a standard normal random variable
μ1 = mean under HA
μ0 = mean under H0
σ = population standard deviation
Zα = critical value at significance level of α
n = sample size


which will have more power? one sided or two sided?

with all else being equal, one sided test will have more power