▁experimental ▁psych ology ▁( the ▁analysis ▁of ▁several ▁variables ▁simultaneously ). ▁He ▁believed ▁that ▁behavior al ▁dimensions ▁were ▁too ▁complex ▁and ▁interactive ▁to ▁fully ▁understand ▁variables ▁in ▁isol ation . ▁The ▁classical ▁un ivari ate ▁approach ▁required ▁bringing ▁the ▁individual ▁into ▁an ▁artificial ▁labor atory ▁situation ▁and ▁meas uring ▁the ▁effect ▁of ▁one ▁particular ▁variable ▁on ▁another ▁also ▁known ▁as ▁the ▁" b ivari ate " ▁approach , ▁while ▁the ▁mult ivari ate ▁approach ▁allowed ▁psych olog ists ▁to ▁study ▁the ▁whole ▁person ▁and ▁their ▁unique ▁combination ▁of ▁tra its ▁within ▁a ▁natural ▁environmental ▁context . ▁Mult ivari ate ▁experimental ▁research ▁designs ▁and ▁mult ivari ate ▁statistical ▁anal ys es ▁allowed ▁for ▁the ▁study ▁of ▁" real - life " ▁situations ▁( e . g ., ▁de pression , ▁divor ce , ▁loss ) ▁that ▁could ▁not ▁be ▁manip ulated ▁in ▁an ▁artificial ▁labor atory ▁environment . ▁ ▁C att ell ▁applied ▁mult ivari ate ▁research ▁methods ▁across ▁several ▁int rap erson al ▁psych ological ▁domains : ▁the ▁trait ▁construct s ▁( both ▁normal ▁and ▁ab normal ) ▁of ▁person ality , ▁motiv ational ▁or ▁dynamic ▁tra its , ▁emot ional ▁and ▁m ood ▁states , ▁as ▁well ▁as ▁the ▁diverse ▁array ▁of ▁cogn itive ▁ab ilities . ▁In ▁each ▁of ▁these ▁domains , ▁he ▁considered ▁there ▁must ▁be ▁a ▁finite ▁number ▁of ▁basic , ▁unit ary ▁dimensions ▁that ▁could ▁be ▁identified ▁empir ically . ▁ ▁He ▁drew ▁a ▁comparison ▁between ▁these ▁fundamental , ▁underlying ▁( source ) ▁tra its ▁and ▁the ▁basic