{smcl} {* 4nov2004}{...} {hline} help for {hi:qfrplot} {hline} {title:Quantile plots of fitted and residuals} {p 8 17 2} {cmd:qfrplot} [{it:plottype}] [{cmd:,} {cmd:super} [{cmdab:norm:al}{c |}{cmdab:gauss:ian}] {cmd:combine(}{it:graph_options}{cmd:)} {cmd:fplot(}{it:qplot_options}{cmd:)} {cmd:rplot(}{it:qplot_options}{cmd:)} {it:graph_options}] {title:Description} {p 4 4 2}{cmd:qfrplot} plots quantile plots of fitted values, minus their mean, and residuals from the previous estimation command. Fitted values are whatever {cmd:predict} produces by default and residuals are whatever {cmd:predict, res} produces. Comparing the distributions gives an overview of their variability and some idea of their fine structure. By default plots are side-by-side. {p 4 4 2}The plot type may be one of eight {help twoway} types, namely, {cmd:area}, {cmd:bar}, {cmd:connected}, {cmd:dot}, {cmd:dropline}, {cmd:line}, {cmd:scatter} or {cmd:spike}. {cmd:scatter} is the default. {p 4 4 2}The plot is restricted to the estimation sample. {p 4 4 2}{cmd:qplot} (SJ 4(1) 2004) must be installed. {title:Remarks} {p 4 4 2}A quantile plot shows ordered values versus the so-called plotting positions, or if the {cmd:normal} or {cmd:gaussian} option is specified, the corresponding quantiles of a standard normal (Gaussian) distribution. For n values ordered minimum first, the plotting positions are {bind:(i - a) / (n - 2a + 1)} for i = 1, ..., n, where a is by default 0.5. {p 4 4 2}W.S. Cleveland in {it:Visualizing data} (Hobart Press, Summit, NJ, 1993) gives many side-by-side quantile plots of fit and residuals, which he calls "residual-fit spread plots". See example on p.41. However, he also uses this term for side-by-side time series plots of fit and residuals. See example on p.157. The command name and description here emphasise the use of a quantile plot. {title:Options} {p 4 8 2}{cmd:super} specifies that plots are to be superimposed, not side-by-side. If {cmd:super} is specified, use {cmd:combine()} to control other characteristics of the combined plot. {p 4 8 2}{cmd:normal} specifies that standard normal quantiles should be shown instead of plotting positions. {cmd:gaussian} is an exact synonym except that by default the text {cmd:Gaussian} will appear within the axis title, rather than {cmd:normal}. {p 4 8 2}{cmd:fplot()} specifies options of {help qplot} controlling the quantile plot of fitted values. {cmd:fplot()} is irrelevant if {cmd:super} is also specified. {p 4 8 2}{cmd:rplot()} specifies options of {help qplot} controlling the quantile plot of residuals. {cmd:rplot()} is irrelevant if {cmd:super} is also specified. {p 4 8 2}{cmd:combine()} specifies options of {help qplot} controlling the quantile plot of fitted and residuals, whenever {cmd:super} is also specified; and options of {help graph combine} otherwise. {p 4 8 2}{it:graph_options} are other graph options affecting the combined graph. {title:Examples} {p 4 8 2}{cmd:. use auto}{p_end} {p 4 8 2}{cmd:. regress mpg weight}{p_end} {p 4 8 2}{cmd:. qfrplot} {p 4 8 2}{cmd:. glm mpg weight, link(power -1)}{p_end} {p 4 8 2}{cmd:. qfrplot, norm fplot(yla(,ang(h)))} {title:Author} {p 4 4 2}Nicholas J. Cox, University of Durham, U.K.{break} n.j.cox@durham.ac.uk {title:Also see} {p 4 13 2}On-line: help for {help qplot}, {help modeldiag}