Ch. 12 - Understanding p Values and Effect Size Indicators.pdf
Ch. 12 - Understanding p Values and Effect Size Indicators
Monday, December 17, 2012 11:13 AM
PSYC2520: Introduction to Experimental Psychology
BeginningBehavioralResearch: A Conceptual Primer (7thed. 2012)Rosnow& Rosenthal
Chapter12: Understandingp Valuesand EffectSize Indicators (pp.219-225)
Why is it importantto focus not just on statistical significance?
• Null hypothesis sigficance testing (NHST)- The use of statistics and probabilities to evaluate the null hypothesis
• Null hypothesis- there is no difference in the dependent variable between any levels of the independent variable
• Significance test = Size of effect x Size of study
○ Effect size is measured using correlations (r)
What is thereasoningbehindnull hypothesissignificance testing?
• Null hypothesis vs. alternative hypothesis
What is thedistinctionbetween a Type I error and a Type II error?
• Type I error implies that he decision maker mistakenly rejected the null hypothesis when it is, in fact, true and
should not have been rejected
○ The risk (or probability) of making a Type I error is called:
• Type II error implies that the decision maker mistakenly failed to reject the null hypothesis whet it is, in fact,
false and should have been reject
○ The risk of making a Type II error is called beta (β)
What are one-tailed and two-tailedp values?
• The two-tailed p value is applicable when the alternative hypothesis did not specifically predict in which side (or
tail) of the probability distribution the significance would be detected
• The on