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help wtp
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Title

    wtp - Confidence intervals for willingness to pay measures.


Syntax

        wtp namelist [,options]

    options             Description
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      delta             delta method (the default)
      fieller           Fieller's method
      krinsky           Krinsky Robb (parametric bootstrap) method
      reps(#)           Set the number of repetitions for the Krinsky Robb
                          method; default is reps(1000)
      seed(#)           Set the seed; default is seed(5426)
      level(#)          Set the confidence level
      equation(name)    Specify the equation name

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Description

    wtp estimates confidence intervals for willingness to pay (WTP) measures
    of the type -b_k/b_c, where b_c is the cost coefficient and b_k is the
    coefficient for attribute x_k.  It uses one of three methods: the delta
    method, Fieller's method or the Krinsky Robb (parametric bootstrap)
    method. See Hole (2007) for a comparison of the accuracy of the methods
    in this context.

    Any number >1 of variable names may be specified. The first is taken to
    be the cost variable, i.e. the variable which coefficient is the
    denominator in the ratios. wtp returns and displays a 3xk matrix, r(wtp),
    where k is the number of specified variables other than the cost
    variable. The first row in r(wtp) contains the WTP estimates and the
    second and third rows contain the lower and upper confidence limits of
    the WTP estimates.

    wtp does not feature a (non-parametric) bootstrap option, since bootstrap
    confidence intervals can easiliy be obtained using the bootstrap command
    (see bootstrap).

    Note: wtp accepts "_cons" as a variable name. Shorthand conventions for
    variable names such as xvar* or xvar1-xvar3 are not accepted, however -
    all names must be written in full.


Options

    delta; use the delta method to construct the confidence intervals (the
        default).

    fieller; use Fieller's method to construct the confidence intervals.

    krinsky; use the Krinsky Robb (parametric bootstrap) method to construct
        the confidence intervals.

    reps(#) sets the number of repetitions for the Krinsky Robb method;
        default is reps(1000).

    seed(#) sets the random-number seed; default is seed(5426). This option
        is only relevant for the Krinsky Robb method.

    level(#) sets the confidence level; default is level(95).

    equation(name) specifies the equation name. This option is relevant if
        wtp is used after multiple-equation models such as mlogit. If the
        equation name is not specified the default is the first equation.


Examples

    . probit choice wait cost knows thoro

    . wtp cost wait knows
    . wtp cost wait thoro _cons, fieller level(90)
    . wtp cost wait knows thoro, krinsky reps(2000)


References

    Hole AR. 2007. A comparison of approaches to estimating confidence
        intervals for willingness to pay measures. Health Economics 16,
        827-840.  http://dx.doi.org/10.1002/hec.1197


Author

    This command was written by Arne Risa Hole (a.r.hole@sheffield.ac.uk),
        Department of Economics, University of Sheffield. I am grateful to
        Jesper Kjær Hansen for helpful comments. Comments and suggestions are
        welcome.