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Choosing the Appropriate Statistics Dr. Erin Devers October 17, 2012 Quantitative or Qualitative? Is the data quantitative or qualitative? If qualitative, you have to do the hard work of coding the material numerically before analyzing it. Level of Measurement? Nominal Descriptive stats: mode Inferential stats: chi-square Ordinal Descriptive stats: median Interval/Ratio Descriptive stats: mean and standard deviation Inferential stats: it depends Chi-Square (ϰ2) Indicates whether a distribution of frequencies is what you would expect If distribution is significantly different from what is expected, then it suggests there is a true difference present Examples Example: Are more males or females diagnosed with schizophrenia? Male 50 Female 50 Guys Girls 70 30 * p < .001 Interval/Ratio Data: Did you conduct an experiment? Correlation and Regression t-test, ANOVA Correlation Joke Correlation Coefficient: Definition: number that represents the relationship between two variables. Answers the question, how are changes in X related to changes in Y? Gives you information regarding Strength of the relationship Direction of the relationship Linear Regression Basic premise: given previous observations, one can (within some range of error) predict what is likely to occur in future Examples: GRE scores and performance in grad school Parental smoking and smoking in teens Cholesterol level and risk for heart attack. Maternal depression and childhood psychopathology Workers level of responsibility and job satisfaction Beliefs and what one will do within a certain situation. t-tests Provide a way to compare two group means with each other Paired or Independent (depends on whether you used a between or within subjects design) ANOVA: Analysis of Variance F statistic Takes into account the fact that chances of getting a difference randomly goes up with multiple comparisons. F = t2 Comparing means of multiple groups e.g. What dose of a drug works best for arresting hallucinations in schizophrenia? Questions?
