The langth of time that the employee works at the firm clearly appears to matter. But maybe the attempts to enhance self-efficacy shouldn't be dismissed so quickly. The researcher must examine both the effects of each experimental variable considered alon and the effects due to combinations of variables. A main effect refers to the experimental difference in means between the different levels of any single experimental variable. In this case, there are potential main effects for the self-efficacy treatment and for the length of time as an employee, but only the differences associated with employment length are significant ( at a .05 level ). An interaction effect is due to a specific combination of independent variables. In this case, it's possible that the combination of length of length of employment and the self-efficacy treatment creates effects that are not clearly represented in the main effects. Interaction results are often shown with a line graph as shown in the following figure.
Main effects are illustrated when the lines are at different heights as is the case here. Notice the line for new employees is higher than the line for current employees. When the lines have very different slopes, an interaction is likely present. In this case, the combination of lenght of employment and self-efficacy treatment is presenting an interaction leading for the following interpretation. The worst situation is the currents employees who do not receive positive feedback. Conversely, the best scenario regarding job satisfaction occurs when the treatment is greater for the employees. It also appears that job satisfaction tends to decrease over time. The benefit of the self-efficacy treatment is greater for the employees that have been with the organization than for new employees. In other words, it appears that the self-efficacy treatment helps prevent the decline in job satisfaction.