Dear listmembers:
I'm working my way through learning how to use regressions other than OLS within stata. One model I frequently use in Excel is the exponential fit. I believe the following is the way to specify that model within Stata's nl function:
nl(y = {beta}*exp({alpha}*x)
I have used the predict function following this estimation to generate a fit and graphed the results, which look like the chart I was expecting to see. I then looked for a way to generate confidence intervals for the fit, and have run aground. It looks like the predictnl function would do what I want, but I can't get it to work. Here's what I've tried:
(after first -drop-ing the fit variable I made with -predict-)
. predictnl fit = predict(fit), ci(ub lb)
Result: fit not allowed \\\ predict(fit) invalid
. predictnl fit = nl (y = {beta}*exp({alpha}*x)), ci(ub lb)
Result: Unknown function nl()
. predictnl fit = y = {beta}*exp({alpha}*x), ci(ub lb)
Result: =exp not allowed
Also, is it possible to use the stored estimation command interactively to solve for a specific x?
e.g.: . predicti(0.5)
which returns some value y according to the model?
John Wallace�|�Research Associate�| Test Method Development
AFFYMETRIX, INC. | 3380 Central Expressway | Santa Clara, CA 95051 | Tel:� 408-731-5574 | Fax:� 408-481-0435
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