 # To Select a Descriptive Statistic

## Presentation on theme: "To Select a Descriptive Statistic"— Presentation transcript:

To Select a Descriptive Statistic
Present entire distribution Table or graph? Frequency Distribution Table Scale of measurement? Bar Graph Histogram or Polygon Summarize entire distribution Central tendency Skewed, open-ended, or undetermined scores? Mean Median Mode Variability What measure of central tendency? Standard Deviation Semi-interquartile range or Range Nominal scale? Range or Semi-Interquartile Range None Describe individual score z-Score Percentile Ranks Table Nominal or Ordinal Graph Interval or Ratio No Interval or Ratio Yes Ordinal Nominal Mean Median No Mode Yes Location relative to the mean Standing relative to other scores

To Select a Statistic to Measure the Relationship Between Two Variables
Data consist of 2 scores for each individual How many dichotomous variables? Both variables measured on interval or ratio scale? Measure linear or monotonic relationship? Pearson Correlation Spearman Correlation Both variables measured on ordinal scales? If possible, rank order both variables and use Spearman. Otherwise, convert to frequency data and use chi-square test for independence. Point-Biserial Correlation Phi-Coefficient Data consist of frequency values for each category Chi-Square Test for Independence Linear Yes Monotonic Yes None No No Only one Two

To Select a Parametric Statistic to Evaluate Group Differences
How many separate samples? How many scores for each subject? Is σ known? z-score Test Single-Sample t-Test Related-Samples t-Test Repeated-Measures ANOVA Matched or independent samples? Related-Samples t-Test Independent-Measures t-Test How many independent variables? Single-Factor ANOVA Two-Factor ANOVA Yes One No Two More than two One Matched Two Independent More than two Matched One Independent Two

To Select a Nonparametric Statistic to Evaluate Group Differences
How many separate samples? How many scores for each subject? How many categories of measurement? Chi-Square Goodness of Fit Binomial Test Can difference scores be ranked? Sign Test Wilcoxon Test Matched or independent samples? Can scores be ranked with few tied values? Mann-Whitney Chi-Square Test for Independence Median Test Independent samples only Are scores discrete or continuous? Two or more One Only two Two No One Matched Yes Two Yes Independent No More than two No Discrete Continuous