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Media type:
E-Article
Title:
Consistent Estimation of Site Index Curves Fitted to Temporary Plot Data
Contributor:
Walters, David K.;
Gregoire, Timothy G.;
Burkhart, Harold E.
Published:
Biometric Society, 1989
Published in:
Biometrics, 45 (1989) 1, Seite 23-33
Language:
English
ISSN:
0006-341X;
1541-0420
Origination:
Footnote:
Description:
Instrumental variable estimation is presented as an alternative to ordinary least squares when only temporary plot data are available to fit site index curves. With an instrument that is uncorrelated with site index but positively correlated with age, consistent coefficient estimates can be obtained. Misspecification tests developed by Hausman (1978, Econometrica 46, 1251-1271) and Feldstein (1974, Journal of the American Statistical Association 69, 990-996) are presented which can be used to help decide when instrumental variable estimation is superior to ordinary least squares. Measures of stand density may provide effective instruments for curve fitting because site index is usually unaffected by density. But of five data sets examined, only one provided an effective instrument of this sort. In this one case, however, the instrumental variable estimates were significantly better than those obtained through the more conventional procedure.