{smcl} {.-} help for {cmd:lincheck} {.-} {title:Check linearity of continuous covariate} {p 8 27} {cmd:lincheck} {it:full GLM command} {p 4 4 10} The continuous covariate to be checked for linearity must be first in the list of independent variables. {title:Description} {p 4 4 10} {cmd:lincheck} provides a quick-and-dirty check of whether a continuous covariate in a general linearized model (GLM) is linear in the link function. {cmd:lincheck} makes a new categorical variable that breaks the continuous covariate into quartiles, then re-estimates the GLM using dummy variables for the quartiles, and finally provides a graph of estimated coefficients plotted against the midpoints (actually: medians) of the quartiles. A linear graph supports the assumption of linearity of the continuous covariate. {cmd:lincheck} works with most GLM commands such as regress, logit/logistic, probit, poisson, stcox etc. and their svy-versions. {title:Remarks} {p 4 4 10} {cmd:lincheck} implements a method suggested by Hosmer & Lemeshow (Applied Logistic Regression, 2nd ed., 2000, Wiley, p.99f). Its reason of existence is the fact that linearity of a continuous covariate can be checked in the presence of other covariates in the model. If the graph is not linear, the continuous covariate might have to enter the model linearized. {cmd:fracpoly} can be used to suggest appropriate transformations. Indeed, Hosmer & Lemeshow recommend to use {cmd:fracpoly} in any case, since its results might not always agree with those of {cmd:lincheck}, and the question of linearity should be assessed in the light of the results of both methods. {title:Examples} {p 4 8}{cmd:. lincheck logit smoker age sex weight if syst_bp>120, nolog or}{p_end} {p 4 8}{cmd:. lincheck xi:logit smoker age sex i.race, nolog}{p_end} {p 4 8}{cmd:. lincheck stcox weight sex}{p_end} {p 4 8}{cmd:. lincheck svyprobit smoker weight age sex}{p_end} {p 6 6}The first two examples test linearity for 'age', the others test linearity for 'weight'.{p_end} {title:Author} {p 4 4 10} Alex Gamma, University Hospital of Psychiatry, Research Department, Zurich, Switzerland. Email: gamma@bli.unizh.ch {title:Also see} {p 4 8} Online: help for {view "http://www.stata.com/stb/stb30/sg50/lintrend.hlp":lintrend}, {help fracpoly}, {help lowess} {p_end}