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158 lines
7.0 KiB
Plaintext
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help for ^mlogplot^ - 03Nov2005
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Odds ratio and discrete change plots for multinomial logit
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----------------------------------------------------------
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For odds ratio plots, the results of ^mlogit^ must be in memory; for discrete
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change plots or odds ratio plots using discrete change the results of ^prchange^
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must be in memory. The syntax is:
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^mlogplot^ [varlist] [^, or^atio ^dc^hange ^s^td^(^[^s^|^u^|^0^]...[^s^|^u^|^0^]^)^
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^min(^#^) max(^#^) packed labels p^rob^(^#^) b^asecategory^(^#^)^
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nt^ics^(^#^) n^ote^(^string^)^ ^val^ues ^dcadd(^#^) ^saving(^filename[^,replace^]^)^]
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To create odds ratio plots with coefficients that you have placed into
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matrices (e.g.,to plot coefficients from a published paper):
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^mlogplot,^ ^matrix v^ars^(^varlist^)^ ^s^td^(^[^s^|^u^|^0^]...[^s^|^u^|^0^]^)^
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[^min(^#^) max(^#^) packed labels b^asecategory^(^#^) nt^ics^(^#^) n^ote^(^string^)^
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^saving(^filename[^,replace^]^)^]
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The matrices you must create are discussed below.
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Description
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-----------
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^mlogplot^ takes coefficients either from ^mlogit^ or from other programs that
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estimate the multinomial logit model. When estimates from other programs are
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used they must be passed to ^mlogplot^ as matrices. ^mlogplot^ then plots the
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odds ratios (i.e., exp(b)) and/or the discrete change coefficients. You can
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list the same variable more than once if you want both standardized and
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unstandardized coefficients to be plotted in the same graph. A variety of
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options control the way the final graph looks. The dialog box program ^mlogview^
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provides a convenient front end that allows you to use this program
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interactively.
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^IMPORTANT^: When using coefficients from ^mlogit^, you must be sure that the
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value labels for the dependent variable begin with different letters or
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numbers. Otherwise, the plot might be misleading.
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Options for Plotting Estimates from ^mlogit^
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---------------------------------------------
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^oratio^ indicates that you want to plot the odds ratios (i.e., exp(b)).
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^dchange^ requests plots involving discrete change. To use this option, you
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must have first run ^prchange^. This option does not work with the ^matrix^
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option.
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If ^oratio^ has been specified, this options plots the size of the letters
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proportional to the size of the corresponding discrete change coefficient.
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See ^dcadd^ and ^dcbase^ for further details.
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If ^oratio^ is not specified, ^dchange^ indicates that you want to plot the
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discrete change coefficients.
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^basecategory^ is used for an odds ratio plot to specify which category of
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the outcome measure is to be used as the reference point.
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^labels^ uses variable labels to label each row of the plot. You might need to
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revise your variable labels to make them fit the graph. This option does
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not work with the ^matrix^ option.
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^min(^#^) and max(^#^)^ specify the minimum value and the maximum value on which
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the coefficients are plotted. This is useful if you want to compare
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coefficients from different logits, or produces several plots from the
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same logit.
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^ntics^ sets the number of tic marks to show on the axes. Used along with ^min^
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and ^max^, this allows you to determine the numbering on the axes and the
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location of tic marks.
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^packed^ removes the vertical spacing among the outcome categories. This allows
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up to 11 variables on a single graph. Otherwise, the maximum is 5.
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^prob^ is used for an odds ratio plot to specify that if a coefficient
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contrasting two outcomes is not signficant at this level, a line is to
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be drawn connecting the letters.
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^std(^[^s^|^u^|^0^]...[^s^|^u^|^0^]^)^ specifies the type of coefficient to plot. s specifies
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standardized coefficients; u specifies unstandardized coefficients; 0
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specifies changes from 0 to 1 in discrete change plots. For example,
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std(u0su) indicates that the first variable is unstandardized, the second
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is binary, the third standardized, and the last is unstandardized.
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^dcadd(^#^)^ is rarely used. In odds ratio plots where
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the ^dchange^ option is specified, the size of the letter corresponds to
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the square root of the size of the discrete change coefficient. ^dcadd^ adds
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an amount to each discrete change making the size of all letters larger,
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making it easier to see the letters for small discrete changes. By
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default this quantity is 0. If your letters print too small, you might
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want to increase this by a small amount, say ^dcadd(.03)^.
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Plotting Estimates from Matrices
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--------------------------------
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The ^matrix^ option indicates that estimates are to be obtained from global
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matrices, which are described below. When this option is used, the options
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^prob^ and ^dchange^ are not allowed. All other options can be used.
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^vars(varlist)^ contains the names of the variables whose coefficients you
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want to plot. The names must be in the order you want to plot them and
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must be included in the global ^mnlname^.
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Globals for Plotting Matrices
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-----------------------------
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^mnlbeta^ contains the betas in a matrix where element (i,j) is the j-th
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variable for comparison i relative to the reference category. That is,
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columns are for variables; rows for different contrasts. Note that
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constants are NOT included.
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^mnlname^ contains the names of the variables corresponding to the columns of
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mnlbeta.
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^mnlcatnm^ is a string with labels for the outcome categories. The
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1st category corresponds to the 1st column of mnlbeta, the 2nd to the
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2nd, etc. The label for the reference category should be last. Thus,
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mnlcatnm provides labels for the rows of mnlbeta. The option
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^basecategory^ references which letter in this string represents the
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base category.
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^mnlrefn^ is the number of the category in mnlcatnm that is the reference
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category for the contrasts contained in mnlbeta.
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^mnldepnm^ contains name of dependent variable.
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^mnlsd^ contains the standard deviations for the variables that correspond
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to columns of mnlbeta
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Example using mlogit
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--------------------
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. ^mlogit occ white ed exper,basecategory(5)^
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. ^prchange^
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. ^mlogplot white ed exper, dc std(0ss) min(-2.75) max(.55)^
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Example using matrices
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----------------------
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. ^matrix mnlsd = (2.946427, 13.95936, 2.946427, 13.95936)^
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. ^global mnlname = "W_Educ W_Exper NW_Educ NW_Exper"^
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. ^global mnlrefn = 5^
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. ^global mnlcatnm = "Menial BlueC Craft WhiteC Prof"^
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. ^matrix mnlbeta = (-.83075, -.92255, -.68761, -.41964 \ /*^
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> ^*/ -.03380, -.03145, -.00026, .00085 \ /*^
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> ^*/ -.70126, -.56070, -.88250, -.53115 \ /*^
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> ^*/ -.11084, -.02611, -.15979, -.05209 )^
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. ^matrix mnlbeta = mnlbeta'^
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. ^mlogplot, vars(W_Educ NW_Educ W_Exper NW_Exper) matrix /*^
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> ^*/ std(ssss) note("Effects of Education")
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.-
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Authors: J. Scott Long and Jeremy Freese
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www.indiana.edu/~jsl650/spost.htm
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spostsup@@indiana.edu
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