Sample size and power Flashcards
1
Q
What is sample size?
A
number of subjects in a study
N = all subjects in a study
n = subjects only in a specific condition
2
Q
What are different ways to justify sample size?
A
- explicitly acknowledge the absence of a justification
- using heuristics
- collecting data from entire pop
- choosing sample size based on resources
- performing prior power analysis
3
Q
What is power?
A
- probability of achieving statistical significance when an effect actually exists
- probability of supporting a hypothesis/ rejecting null hypothesis
4
Q
What is a Type 1 error?
A
false positive: where hypothesis supported but is false
5
Q
What is a Type 2 error?
A
false negative: where hypothesis is ejected but is true
6
Q
What is the effect of increasing power on Type 1 and 2 errors?
A
Increasing power reduces Type 1 and 2 errors
7
Q
What is standard error?
A
- estimates difference between the sample and pop stats > standard deviation of sampling stat
- can be reduced by larger samples
8
Q
What is the risk of excessive power?
A
- excessive power can happen in case of excessively large sample
- may produce unimportant statistical relationships
- risk of Type 1 errors
9
Q
What is effect size?
A
serves as practical measure of significance of a relationship between IV and DV
10
Q
What is observed power?
A
- statistical power assuming the effect size estimated from collected data is true
