Group Designs are used with one or more groups of subjects. In a Between-Group Design, different groups are exposed to different levels of the treatment and the effects on the dependent variable for both groups are compared. In our example, we may ask one group to get one hour of sunlight and another group to get two hours of sunlight in a day. If two or more independent variables are being studied with groups, a Factorial Design is used. This allows the researcher to look at the main and interaction effects. Main Effect is the effect of one independent variable (while disregarding effect of other independent variables) on the dependent variable. Interaction Effects are related to two or more independent variables having a combined effect on the dependent variable. If we asked a group of individuals to go out in the sun and socialize with people to see the effects on depression, the main effect would look at exposure to sun and socialization independently and interaction effect would consider both when assessing the levels of depression.
In the above example, we can see that there’s a main effect for socialization when it comes to the independent variables, meaning socialization tends to be the best overall. There’s also a main effect for severe symptoms, meaning severe symptoms are much likely to improve with treatment. XXXXX interaction effect
In Within-Subjects Design, different levels of independent variable are looked at for same group of individuals. It is also called Repeated Measures Design because the measure is repeated for the same group. In fact, the same group can also function as the control group. For example, if we asked a group of subjects to stay inside for a few days and measured their level of depression, then asked them to go out for an hour and then measured depression, and then asked them to go out for two hours, and then measured depression. This can continue for many levels. This is a type of within-subjects design called Single-Group Time-Series Design.
We can also introduce other independent variables. For example, if we asked them to go out for an hour and socialize. Then we asked them to go out for an hour, socialized, and exercise. Now we have multiple independent variables. This is also an example of within-subjects design. Lastly, Mixed Designs incorporate elements from both between-groups and within-subjects design.