| Abstract: |
The ultimate goal of most non-market valuation studies is to obtain welfare
measures i.e. mean and/or median willingness to pay (WTP) and confidence
intervals. While the delta (nlcom) and bootstrap (bs) methods can be used for
constructing such confidence intervals in Stata, they are not recommended
because WTP measures are non-linear functions of random parameters (Creel and
Loomis, 1991). The best and widely used approach, which is not available in
Stata, consists in simulating the confidence intervals using the Krinsky and
Robb procedure (Haab and McConnell, 2002). Hole (2007) has recently introduced
a useful command, wtp, which implements the Krinsky and Robb procedure in
Stata, but does not feature mean and median WTP estimates and their confidence
intervals. I present a Stata command, wtpcikr, which computes mean and median
WTP, confidence intervals using the Krinsky and Robb procedure, achieved
significance level (ASL) for testing the null hypothesis that WTP equals zero,
and a relative efficiency measure (Loomis and Ekstrand, 1998). The command
supports both linear and exponential contingent valuation models estimated
with or without covariates using the Stata commands probit, logit, biprobit,
and xtprobit. I will illustrate the use of wtpcikr by replicating empirical
results in Haab and McConnell (2002). |