▁that ▁are ▁hypoth es ized ▁to ▁reflect ▁the ▁variation . ▁The ▁term ▁is ▁generally ▁associated ▁with ▁experiments ▁in ▁which ▁the ▁design ▁introdu ces ▁conditions ▁that ▁directly ▁affect ▁the ▁variation , ▁but ▁may ▁also ▁refer ▁to ▁the ▁design ▁of ▁quasi - ex per iments , ▁in ▁which ▁natural ▁conditions ▁that ▁influence ▁the ▁variation ▁are ▁selected ▁for ▁observation . ▁ ▁In ▁its ▁simplest ▁form , ▁an ▁experiment ▁a ims ▁at ▁predict ing ▁the ▁outcome ▁by ▁introdu cing ▁a ▁change ▁of ▁the ▁pre cond itions , ▁which ▁is ▁represented ▁by ▁one ▁or ▁more ▁independent ▁variables , ▁also ▁referred ▁to ▁as ▁" input ▁variables " ▁or ▁" predict or ▁variables ." ▁The ▁change ▁in ▁one ▁or ▁more ▁independent ▁variables ▁is ▁generally ▁hypoth es ized ▁to ▁result ▁in ▁a ▁change ▁in ▁one ▁or ▁more ▁dependent ▁variables , ▁also ▁referred ▁to ▁as ▁" output ▁variables " ▁or ▁" response ▁variables ." ▁The ▁experimental ▁design ▁may ▁also ▁identify ▁control ▁variables ▁that ▁must ▁be ▁held ▁constant ▁to ▁prevent ▁external ▁factors ▁from ▁affect ing ▁the ▁results . ▁Ex perimental ▁design ▁involves ▁not ▁only ▁the ▁selection ▁of ▁suitable ▁independent , ▁dependent , ▁and ▁control ▁variables , ▁but ▁planning ▁the ▁delivery ▁of ▁the ▁experiment ▁under ▁statist ically ▁optimal ▁conditions ▁given ▁the ▁constraints ▁of ▁available ▁resources . ▁ ▁There ▁are ▁multiple ▁approaches ▁for ▁determ ining ▁the ▁set ▁of ▁design ▁points ▁( unique ▁combinations ▁of ▁the ▁settings ▁of ▁the ▁independent ▁variables ) ▁to ▁be ▁used ▁in ▁the ▁experiment . ▁ ▁Main ▁concerns ▁in ▁experimental ▁design ▁include ▁the ▁establishment ▁of ▁valid ity , ▁reli ability , ▁and