▁of ▁other ▁expert ▁witness es . ▁ ▁Un like ▁a ▁test ifying ▁expert , ▁a ▁non - test ifying ▁expert ▁can ▁be ▁easily ▁with dra wn ▁from ▁a ▁case . ▁ ▁It ▁is ▁also ▁possible ▁to ▁change ▁a ▁non - test ifying ▁expert ▁to ▁a ▁test ifying ▁expert ▁before ▁the ▁expert ▁dis closure ▁date . ▁ ▁United ▁States ▁In ▁the ▁United ▁States , ▁under ▁the ▁Federal ▁Rule ▁of ▁Ev idence ▁ 7 0 2 ▁( F RE ), ▁an ▁expert ▁witness ▁must ▁be ▁qualified ▁on ▁the ▁topic ▁of ▁testim ony . ▁In ▁determ ining ▁the ▁qual ifications ▁of ▁the ▁expert , ▁the ▁F RE ▁requires ▁the ▁expert ▁have ▁had ▁special ized ▁education , ▁training , ▁or ▁practical ▁experience ▁in ▁the ▁subject ▁matter ▁rel ating ▁to ▁the ▁case . ▁The ▁expert ' s ▁testim ony ▁must ▁be ▁based ▁on ▁facts ▁in ▁evidence , ▁and ▁should ▁offer ▁opinion ▁about ▁the ▁caus ation ▁or ▁correlation ▁to ▁the ▁evidence ▁in ▁drawing ▁a ▁conclusion . ▁ ▁Exper ts ▁in ▁the ▁U . S . ▁typically ▁are ▁paid ▁on ▁an ▁hour ly ▁basis ▁for ▁their ▁services ▁in ▁investig ating ▁the ▁facts , ▁prepar ing ▁a ▁report , ▁and ▁if ▁necessary , ▁test ifying ▁during ▁pre - tri al ▁discovery , ▁or ▁at ▁trial . ▁H our ly ▁fe es ▁range ▁from ▁approximately ▁$ 2 0 0 ▁to ▁$ 7 5 0 ▁or ▁more ▁per ▁hour , ▁varying ▁primarily ▁by ▁the ▁expert ' s ▁field ▁of ▁expert ise , ▁and ▁the ▁individual ▁expert ' s ▁qual ifications ▁and ▁reputation .