▁period ▁pre val ence , ▁or ▁sometimes ▁cum ulative ▁inc idence . ▁Att ention ▁is ▁focused ▁mostly ▁on ▁whether ▁pre val ence ▁is ▁increasing ▁with ▁time . ▁ ▁Inc idence ▁and ▁pre val ence ▁Ep ide mi ology ▁defines ▁several ▁measures ▁of ▁the ▁frequency ▁of ▁occurrence ▁of ▁a ▁disease ▁or ▁condition : ▁The ▁inc idence ▁rate ▁of ▁a ▁condition ▁is ▁the ▁rate ▁at ▁which ▁new ▁cases ▁occurred ▁per ▁person - year , ▁for ▁example , ▁" 2 ▁new ▁cases ▁per ▁ 1 , 0 0 0 ▁person - year s ". ▁The ▁cum ulative ▁inc idence ▁is ▁the ▁proportion ▁of ▁a ▁population ▁that ▁became ▁new ▁cases ▁within ▁a ▁specified ▁time ▁period , ▁for ▁example , ▁" 1 . 5 ▁per ▁ 1 , 0 0 0 ▁people ▁became ▁new ▁cases ▁during ▁ 2 0 0 6 ". ▁The ▁point ▁pre val ence ▁of ▁a ▁condition ▁is ▁the ▁proportion ▁of ▁a ▁population ▁that ▁had ▁the ▁condition ▁at ▁a ▁single ▁point ▁in ▁time , ▁for ▁example , ▁" 1 0 ▁cases ▁per ▁ 1 , 0 0 0 ▁people ▁at ▁the ▁start ▁of ▁ 2 0 0 6 ". ▁The ▁period ▁pre val ence ▁is ▁the ▁proportion ▁that ▁had ▁the ▁condition ▁at ▁any ▁time ▁within ▁a ▁stated ▁period , ▁for ▁example , ▁" 1 5 ▁per ▁ 1 , 0 0 0 ▁people ▁had ▁cases ▁during ▁ 2 0 0 6 ". ▁ ▁When ▁studying ▁how ▁dise ases ▁are ▁caused , ▁inc idence ▁rates ▁are ▁the ▁most ▁appropriate ▁measure ▁of ▁disease ▁frequency ▁as ▁they ▁assess