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Lecture 13

# Bio2244 Lecture 13 and 14.docx

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Western University

Biology

Biology 2244A/B

Angela White

Fall

Description

Lecture 13, 14
Overview
- Hypothesis – statement about property of population
- Hypothesis test – procedure to test that statement
- Use RARE EVENT RULE
o If P-VALUE IS LESS THAN ALPHA, the assumption is not correct
o In other words, we reject the null hypothesis
Basics
- Null hypothesis (H0) – statement is equal to population parameter
- Alternative hypothesis (Ha or H1) – statement is different than population parameter
- Test statistics
o Value made from sample data
- Critical region
o Values that cause us to REJECT THE NULL HYPOTHESIS
o Typically small values
- Significance level (ALPHA)
o Probability that test statistic is in critical region when NULL IS TRUE
o So it’s a mistake
o If question asked is DIRECTIONAL – ALPHA IS ON ONE SIDE
if not, ALPHA SPLITS INTO TWO
- Critical value
o Value that separates critical region from values of test statistic that don’t reject the
null hypothesis
- P-VALUE
o KNOW WHAT THE QUESTION IS ASKING (DIRECTIONALITY)
o REMEMBER, PROBABILITIES FOR Z-SCORES ARE MEASURED STARTING FROM THE LEFT
o Reject null if P-value <= alpha (significance level)
- Conclusions
o Fail to reject the null Error Types
- Type I error – rejecting null when it is true
o Significance level (ALPHA) represents probability of type I error
- Type II error – not rejecting null when it is false
o BETA used to represent
- To control
o Fixed alpha – increase n to decrease beta
o Fixed n – decrease in alpha will increase beta and vise versa
o INCREASE SAMPLE SIZE to decrease alpha and beta
- POWER
o 1-beta
o Probability of rejecting a false null
o This is good
o Small sample size = lower power
Comprehensive Hypothesis Testing
- For two tailed – confidence interval of 1-alpha
- F

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