what is the relationship between a fixed effect and a time constant in statistics how do you figure out the individual effects of gravity in stata how to estimate global trade flows by fixed and time constant variables how can i estimate individual effects from fim which model uses fixed effect gravity how to estimate xtreg using fixed effects why can i use fixed effects gravity in stata can stata regress fixed effect what model to use for estimating fixed effect how to use fixed effect gravity model what is fixed-effects gravity can you use time constants or fixed effects how to estimate the individual effects of a fixed effect model why use fixed effects gravity model how do you estimate the individual effects of gravity in stata what is the difference between an individual and fixed effect gravity model why can't you estimate the individual effects in stata? how to estimate the individual effects in the FEM model how is the individual effects model determined in stata what is the simplest model to use for forecasting?