Types of tests Flashcards
Describe the Pearson’s r
- Assessing relationships
- Most widely used correleation coefficient
- An effect size, ranges between -1 (perfect negative relationship) to +1 (perfect positive relationship) ((-).1-.3: small effect, (-).3-.5: medium effect, (-).5.-1: large effect)
- Assumptions:
- Two continuous variables (interval or ratio)
- Normally distributed data
- Independent observations
- Linear relationships
- Non parametric alternatives: Spearman’s rho, Kendall’s tau, Point Biserial Correlation
Describe Spearman’s Rho and Kendall’s tau
- Assessing relationships
- The non-parametric alternatives to Pearson’s r
- Can be used when one or both variables are ordinal or when normality assumptions aren’t met
- Based on ranks of scores
- Use Kendall’s tau if many tied ranks!
Describe the Point Biserial Correlation
- Assessing relationships
- Can be used when one variable is binary and the other is continuous
- Calculated using Pearson’s r formula
Describe the linear regression
- Exploring predictions
- Used to predict the value of a continuous outcome variable using the value of a single (continuous) predictor variable
- Assumptions:
- linear relationships
- two continuous variables
- Normal distribution
- Independent observations
- Homoscedasticity
Describe the independent t-test
- Assessing differences, 2 groups, independent design
- Tests whether means differ for two independent groups that we have collected data for (e.g. average grades of AU and CPH psychology students)
- Assumptions:
- Outcome variable (DV) must be continuous
- Grouping variable (IV) must be categorical and binary (2 categories)
- Normally distributed DV data
- Groups must be mutually exclusive
- Homogeneity of varaince (similar spread of scores around the mean)
- Test statistic: t
- Effect size: r or d
- Non-parametric alternative: Mann-Whitney U test
Describe the Mann-Whithey U test
- Assessing relationships - independent designs
- Non-parametric alternative to an independent t-test!
- Tests whether medians differ for two independent groups that we have collected data for (e.g. average grades of AU and CPH psychology students)
- Can be used when you have ordinal data or non-normal continuous data
- Uses medians instead of means
- Test statistic: U statistic
- Effect size: r
Describe the dependent t-test
- Assessing relationships - repeated measures designs
- Tests wheter the means for two conditions differ within a single group (e.g. psychology student’s grades in statistics vs work psychology)
- Assumptions:
- Outcome variable (DV) must be continuous
- Grouping variable (IV) must be categorical and binary (2 categories)
- Normally distributed sampling distribution of differences
- Each participant must be in both conditions!
- Test statistic: t
- Non-parametric alternative: Wilcoxon signed-rank
Describe the wilcoxon signed rank-test
- Assessing relationships - repeated measures designs
- Non-parametric alternative to a dependent t-test!
- Can be used when you have non-normal continous data or ordinal data
- Converts all raw data into ranks
- Uses medians instead of means
- Test statistic: T (sum of positive ranks)
- Effect size: r
Describe the independent ANOVA
- Assessing relationships - independent designs
- tests whether means differ for 3+ independent groups that we have collected data for (e.g. average grades of AU, CPH and Odense psychology students)
- an omnibus test (tells us if there are differences, but doesnt specify which means differ)
- Test statistic: F
- Assumptions:
- Outcome variable (DV) must be continuous
- Normal sampling distribution (in each group)
- 3+ levels of groups variable (IV)
- Groups must be mutually exclusive
- Homogeneity of variance
- If significant F: Follow up with post-hoc bonferroni test (t-test comparisons between all groups)
- Non-parametric alternative: Krustal-Wallis test
Describe the Kruskall-Wallis test
- Assessing relationships - independent design
- The non-parametric alternative to an independent ANOVA!
- Can be used to test whether medians differ for 3+ independent groups that we have collected data for (e.g. grades of AU, CPH, Odense psychology students)
- Can be used when you have non-normal continuous data or ordinal data
- Converts all raw data into ranks before analysing them
- Test statistic: H
- Significant H-test: follow up with non-parametric post hoc tests (Mann-Whitney U)
Describe the dependent (repeated-measures) ANOVA
- Assessing relationships - repeated measures design
- Tests whether means differ between 3+ conditions that we have collected data for (e.g. average mean grades for the same AU students in semester 1, semester 2, semester 3)
- An omnibus test (tells us if there are differences, but doesn’t specify which means differ)
- Assumptions:
- Outcome variable (DV) must be continuous
- Normal sampling distribution
- 3+ levels of grouping variable (IV)
- Sphericity
- Test statistic: F
- If F is significant: Follow up with post-hoc bonferroni tests
- Non-parametric alternative: Friedman’s test
Describe the Friedman’s test
- Assessing relationships - repeated measures design
- The non-parametric alternative to a dependent ANOVA!
- Can be used to test whether medians differ for 3+ conditions that we have collected data for (e.g. grades of the same AU students in 1st, 2nd and 3rd semester)
- Can be used when you have non-normal continuous data or ordinal data
- Converts all raw data into ranks before analysing them
- Test statistic: x2
- Significant x2: follow up with non-parametric post hoc test (Wilcoxon signed rank)
Describe the Chi-Square test
- Exploring categorical associations
- Can be used to examine whether, and how, two categorical variables are associated (e.g. what association, if any, exists between political affiliation (democrat/republican) and support for the death penalty (for/against)?)
- Non-parametric
- test statistic: χ2
- DF: (no of rows-1)*(no of coloums-1)
- Effect size: Odds ratio for 2x2 (SPSS: Risk), Cramer’s V for larger
- Assumptions:
- 2 categorical variables (non-parametric)
- Mutually exclusive categories (independence)
- For 2x2 tables, expected frequencies must not be <5
- For larger tables, all expected frequencies must be at least 1, with no more than 20% of cells in the contingency table having expeted frequency <5
What is the non-parametric alternative for an independent t-test?
The Mann-Whitney U test
What is the non-parametric alternative for a dependent t-test?
The Wilcoxon-signed rank test