2 Descriptive Statistics Used to present data in summary form.
3 Inferential statistics Used to determine whether an independent variable had a reliable effect on a dependent variableReplication: repeating experiment to try to get the same results second timeGroups must be equivalentAchieved by experimental control and/or randomization
4 Random errorVariation due to differences among subjects within each groupResponsible for some difference in the means
5 Research and Null Hypotheses Research hypothesisH1: Population means are not equalNull hypothesisHO: Population means are equalThe assumption that the independent variable has had no effect
6 Statistical significance The probability the difference in sample means is due to errorStatistically significant outcome: has a small likelihood of occurring if the null hypothesis is true
7 Level of significance Probability of error chosen by researcher Usually set at .05 or lessAlpha level indicated by Greek letter αNoted as p .05; p .01, etcp: probability
8 Null-Hypothesis Significance Testing Null-hypothesis significance testing assesses the probability of obtaining a given difference between sample meanst-test: commonly used significance test
9 The t-test Interpreting the t-test value: If probability is high (over .05), fail to reject the null hypothesisIf probability is low (.05 or less), reject the null hypothesis
10 Do we have a winner? Data Analysis for an Experiment Comparing Means Round Chopsticks?Did the independent variable (shape of chopsticks) have an effect on the dependent variable (number of pasta pieces transferred)?Square Chopsticks?
11 Null Hypothesis Significance Testing: The t Test One-tailed versus two-tailed testsOne-tailed test = research hypothesis specified a direction of difference between the groupsTwo-tailed test = research hypothesis did not predict direction of difference
12 Chopsticks ChallengeHypothesis #1: Performance when using round chopsticks is different (better or worse) than performance when using square chopsticks(two-tailed) = .19Hypothesis #2: Performance when using round chopsticks is better than performance when using square chopsticks(one-tailed) = .09
13 Do we accept the null hypothesis if the independent variable did not have an effect? Instead we fail to reject the null hypothesis.
14 Type I and Type II Errors Decision to reject the null hypothesis is based on probabilities rather than certainties.Decision may or may not be correct
15 Type I errorOccurs when the null hypothesis is rejected, but the null hypothesis is true
16 Type II errorOccurs when the null hypothesis is false, but it is not rejected
17 Experimental sensitivity Occurs when an experiment detects an effect of the independent variable (when, in fact, the independent variable truly has an effect)
18 Experimental powerOccurs when a statistical test allows researchers to correctly reject the null hypothesisDetermined by 3 factors:Size of the effectSample sizeLevel of statistical significance