Q. What are fixed and random effects?

Fixed and Random Effects

Fixed Effects:

1) effects of well-defined categories

2) the results helps make inferences at the population level

ex:  In repeated measures, more than one (identical) measurement is taken on the same individual. The "subject" is fixed.

Random Effects:

1) the levels we observe in that group are samples from a larger population

2) the results helps make inferences at the individual level

ex:  If data are collected from different medical centers, “center” might be thought of as random.