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help for ddirifit
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Displaying discrete changes and marginal effects from dirifit output

ddirifit [, at(variables_and_values) iterate(#) ]

Description

ddirifit displays the change in predicted dependent variable for three
types of discrete changes in explanatory variable and the marginal
effects:

Discrete Changes

Min --> Max shows the change in predicted dependent variable when the
explanatory variable changes from its minimum value to its maximum
value, while keeping all other explanatory variables at their
specified values (by default the mean). This is the only effect shown
for dummy variables (variables with only two distinct values).

+-SD/2 shows the change in predicted dependent variable when the
explanatory variable moves from half a standard deviation below its
specified value (by default the mean) to half a standard deviation
above its specified value, while keeping all other variables at their
specified values. In other words: It shows the effect of a standard
deviation change in explanatory variable, centered around the
specified value, on the predicted dependent variable.

+-1/2 shows the change in predicted dependent variable when the
explanatory variable moves from half a unit below its specified value
to half a unit above its specified value, while keeping all other
variables at their specified values. In other words: It shows the
effect of a unit change in explanatory variable, centered around the
specified value, on the predicted dependent variable.

Marginal Effects

MFX at x shows the marginal effect of each (non dummy) variable,
while keeping all variables at their specified values. The marginal
effect is the change in predicted dependent variable for a unit
change in the explanatory variable, assuming that the effect doesn't
change over that interval.

ddirifit is only allowed after dirifit in the alternative
parameterization, i.e. if one or more of muvar(), mu1|2|3|...|k(),
baseoutcome(), and phivar() is specified or if the alternative option is
specified.

Options

at(variables_and_values) allow the user to specify at which values of the
explanatory variables the effects are calculated.
variables_and_values is an alternating list of variables and either
numeric values or mean, median, min, max, p1, p5, p10 p25, p50, p75,
p90, p95, p99. The default is mean for all variables. The statistics
p1, p5, ..., p99, are the 1st, 5th, ..., 99th percentile.

iterate(#) is passed directly to nlcom. It specifies the maximum number
of iterations used to find the optimal step size in calculating
numerical derivatives. You should rarely have to use this option.
See: nlcom.

Examples

. dirifit propfood, mu(income nchild) phi(haspartner)

. ddirifit

. ddirifit, at(income median nchild 2)

Author

Maarten L. Buis, Vrije Universiteit Amsterdam
m.buis@fsw.vu.nl

Also see

Online: help for dirifit and nlcom

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