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Lecture 13

Bio2244 Lecture 13 and 14.docx

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Western University
Biology 2244A/B
Angela White

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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