{smcl} {* 17may2002}{...} {hline} help for {hi:qfrplot7} {hline} {title:Quantile plots of fitted and residuals} {p 8 16}{cmd:qfrplot7} [ {cmd:,} {cmd:super} {cmdab:r:everse} {cmd:a(}{it:#}{cmd:)} {c -(}{cmdab:norm:al}{c |}{cmdab:gauss:ian}{c )-} {it:graph_options} ] {title:Description} {p}{cmd:qfrplot7} 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}The plot is restricted to the estimation sample. {p}This is the original of {cmd:qfrplot} for Stata 7, renamed {cmd:qfrplot7}. Users of Stata 8 upwards should upgrade to {cmd:qfrplot}. {title:Remarks} {p}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}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 0 4}{cmd:super} specifies that plots are to be superimposed, not side-by-side. {p 0 4}{cmd:reverse} reverses the sort order, so that ordered values are plotted against {bind:1 - plotting position}. {p 0 4}{cmd:a(}{it:#}{cmd:)} specifies a in the formula for plotting position. The default is {bind:a = 0.5}, giving {bind:(i - 0.5) / n}. Other choices include {bind:a = 0}, giving {bind:i / (n + 1)}, and {bind:a = 1/3}, giving {bind:(i - 1/3) / (n + 1/3)}. Rarely will choice of a make any discernible difference. {p 0 4}{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 0 4} {it:graph_options} are options of {cmd:graph, twoway} except for {cmd:by()}. Defaults include {cmd:border gap(5)}. If {cmd:symbol()} is specified, the first symbol is used to plot fitted values and the second symbol to plot residuals. Otherwise, graph options refer to either or both graphs produced, except that {cmd:saving()} and {cmd:title()} refer to the combined graph image. {title:Examples} {p 4 8}{inp:. use auto} {p 4 8}{inp:. regress mpg weight} {p 4 8}{inp:. qfrplot7} {p 4 8}{inp:. glm mpg weight, link(log)} {p 4 8}{inp:. qfrplot7} {p 4 8}{inp:. qfrplot7, norm} {title:Author} Nicholas J. Cox, University of Durham, U.K. n.j.cox@durham.ac.uk {title:Also see} {p 0 19}On-line: help for {help graph}, {help quantile}, {help qnorm}, {help regdiag}, {help regplot} (if installed), {help anovaplot} (if installed), {help ovfplot} (if installed), {help indexplot} (if installed) {p_end}