▁dependent ▁variables , ▁or ▁are ▁both ▁independent ▁and ▁dependent ▁variables , ▁are ▁term ed ▁' end ogen ous '. ▁Graph ically , ▁end ogen ous ▁variables ▁have ▁at ▁least ▁one ▁single - head ed ▁arrow ▁pointing ▁at ▁them . ▁ ▁In ▁the ▁model ▁below , ▁the ▁two ▁ex ogen ous ▁variables ▁( Ex 1 ▁and ▁Ex 2 ) ▁are ▁mode led ▁as ▁being ▁correl ated ▁as ▁dep icted ▁by ▁the ▁double - head ed ▁arrow . ▁Both ▁of ▁these ▁variables ▁have ▁direct ▁and ▁indirect ▁( through ▁En 1 ) ▁effects ▁on ▁En 2 ▁( the ▁two ▁dependent ▁or ▁' end ogen ous ' ▁variables / fact ors ). ▁ ▁In ▁most ▁real - world ▁models , ▁the ▁end ogen ous ▁variables ▁may ▁also ▁be ▁affected ▁by ▁variables ▁and ▁factors ▁stem ming ▁from ▁outside ▁the ▁model ▁( external ▁effects ▁including ▁measurement ▁error ). ▁ ▁These ▁effects ▁are ▁dep icted ▁by ▁the ▁" e " ▁or ▁error ▁terms ▁in ▁the ▁model . ▁ ▁Using ▁the ▁same ▁variables , ▁alternative ▁models ▁are ▁conce iv able . ▁ ▁For ▁example , ▁it ▁may ▁be ▁hypoth es ized ▁that ▁Ex 1 ▁has ▁only ▁an ▁indirect ▁effect ▁on ▁En 2 , ▁deleting ▁the ▁arrow ▁from ▁Ex 1 ▁to ▁En 2 ; ▁and ▁the ▁lik elihood ▁or ▁' fit ' ▁of ▁these ▁two ▁models ▁can ▁be ▁compared ▁statist ically . ▁ ▁There ▁is ▁a ▁computer ▁package ▁called ▁L IS RE L ▁ ▁Path ▁trac ing ▁rules ▁ ▁In ▁order ▁to ▁valid ly ▁calculate ▁the ▁relationship ▁between ▁any ▁two ▁boxes ▁in