A study can have which of the following effects?

In a study, particularly in the context of factorial designs, it is possible to observe both main effects and interaction effects due to the relationships between independent and dependent variables.

Main effects refer to the influence of an independent variable on a dependent variable, averaged across the levels of other independent variables. For example, if you are studying the impact of different types of therapy (independent variable) on depression levels (dependent variable), you might find that one type of therapy leads to lower depression levels, indicating a main effect.

Interaction effects occur when the effect of one independent variable on the dependent variable changes depending on the level of another independent variable. Using the therapy example again, suppose the effectiveness of therapy varies based on the patient's age group. This would suggest that age interacts with therapy type, resulting in a different outcome than would be observed if only one factor was considered.

Studies that include multiple independent variables will typically examine both kinds of effects to provide a comprehensive understanding of how those factors influence the outcome. Thus, observing both main effects and interaction effects is crucial for drawing accurate conclusions from research findings.