Bernard Szlachta at 02:35, 6 March 2016

2016-03-06T02:35:09Z

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{{Cat|Intro to R|082}}

== Type I and Type II errors ==
Real World
Null Hypothesis '''True''' '''False'''
'''Accept''' Correct Decision Type II Error (β)
'''Reject''' Type I Error (α) Correct Decision

== Power ==
Power is the probability of correctly rejecting a false null hypothesis
* E.g. the probability that:
** given there is a difference between the population means
** the sample means will be significantly different
* The probability of failing to reject a false null hypothesis is β
Power = 1 - β

When designing an experiment you know the chance of finding a significant effect.

== Questions ==
Power is:
* The probability that the null hypothesis is true
* The probability that the null hypothesis is false
* The probability a false null hypothesis will be rejected
* The probability a true null hypothesis will be rejected

If the power of an experiment is low then:
* The experiment will likely be inconclusive
* Any significant findings obtained are suspect
* The results are skewed.

== power.* function ==
# Find the sample size
power.t.test(power=0.9,sd=2,sig.level=0.05,delta=3)

# Find the power of the test
power.t.test(n=2,sd=2,sig.level=0.05,delta=3)

== PWR package ==
* pwr.p.test: test for one proportion (ES=h)
* pwr.2p.test: test for two proportions (ES=h)
* pwr.t.test: one sample and two samples (equal sizes) t tests for means (ES=d)
* pwr.t2n.test: two samples (different sizes) t test for means (ES=d)
* pwr.anova.test: test for one-way balanced anova (ES=f)
* pwr.r.test: correlation test (ES=r)
* pwr.f2.test: test for the general linear model
....

== Pwr package ==
<source lang="rsplus">
install.packages("pwr")
library("pwr")
</source>

R - Errors and Power - Revision history

Bernard Szlachta at 02:35, 6 March 2016