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 ( ϰ 2 )  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? MaleFemale 50 GuysGirls 7030 * 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 = t 2  Comparing means of multiple groups e.g. What dose of a drug works best for arresting hallucinations in schizophrenia?

Questions?