please i required the sampled required the sampled firms to have at least five observations in the data set WHAT The code i need to add to my regression

reg pensionassetallocationequitywh csopresence firmsizewh ROAwh operationcashflowvolatilitywh leveragewh dividendpayoutwh boardsizewh boardindependencewh contribu
tionwh pension_sizewh durationwh planreturnswh discountratewh mergersaquisitions i.sic i.year