how do you get period effects in r how do i regress pphpy in r how to regress pphpy pphpy is a factor variable what is pphpy what is PPHY used for in r how to find period effects how to calculate period for pphpy in r what does pphpy stand for in regression what is pphpy how to calculate pphpy from age group how to find out the dummies of the age group in r how to find out if age group is a r period calculating period in r how to get age effects in r which age group is affected by age regression? how do i regress age group how to find out if the year is a factor or a time series regression if you pool data do you get period effects how to calculate pphpy in r