Hi Reeza, I have fix the first error but it still give me another error and warning like the following: 567 568     /* Linear Approximate AIDS (LA-AIDS) Model*/ 569  ods html; 570 571     proc model data=aids ; 572     /*imposing homogeneity and symmetry restrictions on the parameters*/ 573        gclpii = 0-gclcl-gclpl-gclbl-gclci-gclai; 574        gplpii = 0-gclpl-gplpl-gplbl-gplci-gplai; 575        gblpii = 0-gclbl-gplbl-gblbl-gblci-gblai; 576        gcipii = 0-gclci-gplci-gblci-gcici-gciai; 577        gaipii = 0-gclai-gplai-gblai-gciai-gaiai; 578        gpiipii = 0-gclpii-gplpii-gblpii-gcipii-gaipii-gpiipii; 579        acl + apl + abl + aci + aai + apii = 1; 580     /* delete last equation(pii) for adding up*/ 581        wcl = acl + gclcl*lpcl + gclpl*lppl + gclbl*lpbl + gclci*lpci + gclai*lpai + 581! gclpii*lppii + bcl*lxp; 582        wpl = apl + gclpl*lpcl + gplpl*lppl + gplbl*lpbl + gplci*lpci + gplai*lpai + 582! gplpii*lppii + bpl*lxp; 583        wbl = abl + gclbl*lpcl + gplbl*lppl + gblbl*lpbl + gblci*lpci + gblai*lpai + 583! gblpii*lppii + bbl*lxp; 584        wci = aci + gclci*lpcl + gplci*lppl + gblci*lpbl + gcici*lpci + gciai*lpai + 584! gcipii*lppii + bci*lxp; 585        wai = aai + gclai*lpcl + gplai*lppl + gblai*lpbl + gciai*lpci + gaiai*lpai + 585! gaipii*lppii + bai*lxp; 586        fit wcl wpl wbl wci wai / sur outest=fin0 587                      converge = .0000001 maxit = 1000 ; 588 589        parms acl  bcl gclcl gclpl gclbl gclci gclai gclpii 590              apl  bpl       gplpl gplbl gplci gplai gplpii 591              abl  bbl             gblbl gblci gblai gblpii 592              aci  bci                   gcici gciai gcipii 593              aai  bai                         gaiai gaipii 594              apii                                   gpiipii; 595      estimate 'elasticity cl' ((gclcl - (bcl*.138))/.138) -1; 596 597     run; WARNING: The 'parameter' gclpii is assigned a value by the model program. This parameter will          not be estimated. WARNING: The 'parameter' gplpii is assigned a value by the model program. This parameter will          not be estimated. WARNING: The 'parameter' gblpii is assigned a value by the model program. This parameter will          not be estimated. WARNING: The 'parameter' gcipii is assigned a value by the model program. This parameter will          not be estimated. WARNING: The 'parameter' gaipii is assigned a value by the model program. This parameter will          not be estimated. ERROR: At OLS Iteration 0 there are 0 nonmissing observations available. At least 5 are needed        to compute the next iteration. NOTE: The data set WORK.FIN0 has 0 observations and 29 variables. 598     quit ; ... View more