what are the variables in the fixed effect in statistics why do you need to put random variables in a fixed model can you use the time and year variables in a mixed model when to use a time variable in mixed model how long is the time variable in lmer for a period or year how many variables should i use in lmer can you use a time variable in a mixed data set how to fit a variable in a data set when is a fixed effect applied in a data set how to fit a variable for a fixed effect does time affect random effects? time variable in longitudinal model when calculating a variable when to use random variables in linear models can lmer use time variable is it good to use a time variable in mixed data time variable variable in longitudinal data set when to insert lmer variable for a variable what is the fixed effect on lmer why should a fixed period variable be chosen when modelling sales?