Parametric Statistics
Partido, B.B.
Comparing 2 groups
In general, t-tests assess whether the means of two groups are statistically different from each other when the data is parametric (continuous data- interval-scale or ratio-scale). These include the following:
- independent samples t-test
- dependent samples t-test
| Independent samples t-test | Dependent samples t-test | |
| Independent variable (grouping) | nominal scale (dichotomous) | nominal scale (dichotomous) |
| Dependent variable (outcome of interest) | interval or ratio scale | interval or ratio scale |
| Purpose | Compares the means of 2 unrelated groups | Compares the means of 2 related groups |
| What the test reports | Mean and standard deviation of each group | Mean and standard deviation of each group |
An example of an independent samples t-test: You want to determine whether there are differences in plaque score (dependent variable-ratio scale) among teenage males and females (independent variable-nominal scale).
An example of a dependent samples t-test: You want to determine whether the plaque score of teenagers (dependent variable-ratio scale) would change from week 0 to week 2 (independent variable- nominal scale) upon visualizing their bacteria on a microscope.
Comparing 3 or more groups
A one-way ANOVA compares the means of three or more independent groups defined by one factor (grouping variable) when the data is parametric (continuous data- interval-scale or ratio-scale).
| One-way ANOVA | |
| Independent variable (grouping) | nominal scale |
| Dependent variable (outcome of interest) | interval or ratio scale |
| Purpose | Compares the means of 3 or more unrelated groups |
| What the test reports |
Reports if one or more of the means are statistically significantly different from the others. Post-hoc tests are completed to determine which groups are different.
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An example of a one-way ANOVA: You want to determine whether the plaque score (dependent variable-ratio scale) of male and female teenagers (independent variable- nominal scale) would change from week 0 to week 2 (independent variable- nominal scale) upon visualizing their bacteria on a microscope.