- series ▁analysis ▁to ▁economic ▁data . ▁Contempor ary ▁research ▁on ▁time ▁series ▁statistics ▁consider ▁additional ▁form ulations ▁of ▁station ary ▁processes , ▁such ▁as ▁ ▁autor eg ress ive ▁moving ▁average ▁models . ▁More ▁general ▁models ▁include ▁ ▁autor eg ress ive ▁conditional ▁heter os ked astic ity ▁( AR CH ) ▁models ▁and ▁generalized ▁AR CH ▁( G AR CH ) ▁models . ▁ ▁Non - st ochastic ▁mathematical ▁models ▁may ▁be ▁purely ▁qual itative ▁( for ▁example , ▁models ▁involved ▁in ▁some ▁aspect ▁of ▁social ▁choice ▁theory ) ▁or ▁quant itative ▁( in vol ving ▁rational ization ▁of ▁financial ▁variables , ▁for ▁example ▁with ▁hyper bol ic ▁coordinates , ▁and / or ▁specific ▁forms ▁of ▁functional ▁relationships ▁between ▁variables ). ▁ ▁In ▁some ▁cases ▁economic ▁predictions ▁of ▁a ▁model ▁merely ▁assert ▁the ▁direction ▁of ▁movement ▁of ▁economic ▁variables , ▁and ▁so ▁the ▁functional ▁relationships ▁are ▁used ▁only ▁in ▁a ▁qual itative ▁sense : ▁for ▁example , ▁if ▁the ▁price ▁of ▁an ▁item ▁increases , ▁then ▁the ▁demand ▁for ▁that ▁item ▁will ▁decrease . ▁ ▁For ▁such ▁models , ▁econom ists ▁often ▁use ▁two - dimensional ▁graphs ▁instead ▁of ▁functions . ▁ ▁Qual itative ▁models ▁are ▁occasionally ▁used . ▁One ▁example ▁is ▁qual itative ▁scenario ▁planning ▁in ▁which ▁possible ▁future ▁events ▁are ▁played ▁out . ▁Another ▁example ▁is ▁non - numer ical ▁decision ▁tree ▁analysis . ▁Qual itative ▁models ▁often ▁suffer ▁from ▁lack ▁of ▁precision . ▁ ▁Example : ▁The ▁effect ▁of ▁a ▁corpor ate ▁tax ▁cut ▁on ▁w ages ▁