▁to ▁variation ▁and ▁measurement ▁uncertainty ; ▁thus ▁they ▁are ▁repeated ▁and ▁full ▁experiments ▁are ▁rep licated ▁to ▁help ▁identify ▁the ▁sources ▁of ▁variation , ▁to ▁better ▁estimate ▁the ▁true ▁effects ▁of ▁treat ments , ▁to ▁further ▁strength en ▁the ▁experiment ' s ▁reli ability ▁and ▁valid ity , ▁and ▁to ▁add ▁to ▁the ▁existing ▁knowledge ▁of ▁the ▁topic . ▁However , ▁certain ▁conditions ▁must ▁be ▁met ▁before ▁the ▁rep lication ▁of ▁the ▁experiment ▁is ▁comm enced : ▁the ▁original ▁research ▁question ▁has ▁been ▁published ▁in ▁a ▁peer - review ed ▁journal ▁or ▁widely ▁c ited , ▁the ▁research er ▁is ▁independent ▁of ▁the ▁original ▁experiment , ▁the ▁research er ▁must ▁first ▁try ▁to ▁rep licate ▁the ▁original ▁find ings ▁using ▁the ▁original ▁data , ▁and ▁the ▁write - up ▁should ▁state ▁that ▁the ▁study ▁conducted ▁is ▁a ▁rep lication ▁study ▁that ▁tried ▁to ▁follow ▁the ▁original ▁study ▁as ▁strictly ▁as ▁possible . ▁ ▁Block ing ▁Block ing ▁is ▁the ▁non - random ▁arrangement ▁of ▁experimental ▁units ▁into ▁groups ▁( block s ) ▁consisting ▁of ▁units ▁that ▁are ▁similar ▁to ▁one ▁another . ▁Block ing ▁reduces ▁known ▁but ▁irrelevant ▁sources ▁of ▁variation ▁between ▁units ▁and ▁thus ▁allows ▁greater ▁precision ▁in ▁the ▁estimation ▁of ▁the ▁source ▁of ▁variation ▁under ▁study . ▁ ▁Orth og on ality ▁ ▁Orth og on ality ▁concerns ▁the ▁forms ▁of ▁comparison ▁( contr asts ) ▁that ▁can ▁be ▁legit imately ▁and ▁efficiently ▁carried ▁out . ▁Con tr asts ▁can ▁be ▁represented ▁by ▁vectors ▁and ▁sets ▁of ▁orthogonal ▁contrast s ▁are