Flashcards in Power and Sample Size Deck (12)
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1
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
2
precision analysis
estimate how large a sample is needed to produce a given level of precision at a fixed confidence level
3
Two types of statistical error
Type 1 error (alpha)
Type 2 error (beta)
4
Statistical power
1-beta; probability that the null hypothesis will be rejected when it is false
5
Under Neyman-Pearson, alpha is
set by investigator
6
Under Neyman-Pearson, beta
is estimated and will be determined by such characteristics as sample size, trait variance and effect size
7
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)
8
as alpha decreases
so will the power. It will decrease
But beta increased
9
given in a fixed sample size:
if alpha increases, beta decreases
if alpha decreases, beta increases
10
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
11
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
12
