▁Are ▁control ▁conditions ▁needed , ▁and ▁what ▁should ▁they ▁be ? ▁ ▁Man ip ulation ▁checks ; ▁did ▁the ▁manip ulation ▁really ▁work ? ▁ ▁What ▁are ▁the ▁background ▁variables ? ▁ ▁What ▁is ▁the ▁sample ▁size . ▁How ▁many ▁units ▁must ▁be ▁collected ▁for ▁the ▁experiment ▁to ▁be ▁general is able ▁and ▁have ▁enough ▁power ? ▁ ▁What ▁is ▁the ▁relev ance ▁of ▁interactions ▁between ▁factors ? ▁ ▁What ▁is ▁the ▁influence ▁of ▁delayed ▁effects ▁of ▁substant ive ▁factors ▁on ▁out comes ? ▁ ▁How ▁do ▁response ▁sh ifts ▁affect ▁self - report ▁measures ? ▁ ▁How ▁feas ible ▁is ▁repeated ▁administration ▁of ▁the ▁same ▁measurement ▁instruments ▁to ▁the ▁same ▁units ▁at ▁different ▁occasions , ▁with ▁a ▁post - test ▁and ▁follow - up ▁tests ? ▁ ▁What ▁about ▁using ▁a ▁proxy ▁pre test ? ▁ ▁Are ▁there ▁l ur king ▁variables ? ▁ ▁Should ▁the ▁client / pat ient , ▁research er ▁or ▁even ▁the ▁anal yst ▁of ▁the ▁data ▁be ▁blind ▁to ▁conditions ? ▁ ▁What ▁is ▁the ▁feas ibility ▁of ▁subsequent ▁application ▁of ▁different ▁conditions ▁to ▁the ▁same ▁units ? ▁ ▁How ▁many ▁of ▁each ▁control ▁and ▁noise ▁factors ▁should ▁be ▁taken ▁into ▁account ? ▁ ▁The ▁independent ▁variable ▁of ▁a ▁study ▁often ▁has ▁many ▁levels ▁or ▁different ▁groups . ▁In ▁a ▁true ▁experiment , ▁research ers ▁can ▁have ▁an ▁experimental ▁group , ▁which ▁is ▁where ▁their ▁inter vention ▁testing ▁the ▁hypothesis ▁is ▁implemented , ▁and ▁a ▁control ▁group , ▁which ▁has ▁all ▁the ▁same ▁element ▁as ▁the ▁experimental