When the factor levels or treatments chosen for study are the specific ones about which we wish to draw conclusions, the model obtained from analysis of such data is called a fixed effects model. The results from the analysis will apply only to the treatments considered in the study and cannot be generalized to similar treatments which were not explicitly included in the experiment.
A pizza bakery is conducting a study on whether the five ovens at the bakery give consistent results when using the same temperature and time settings. These particular five ovens constitute all the factor levels of interest, so the analysis based on these levels will apply only to these ovens. The model is therefore called a fixed effects model.
Random Effects Model