J. Anim Sci.
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Published online first on April 12, 2007
J. Anim Sci. 1990. doi:10.2527/jas.2007-0016
© 2007 American Society of Animal Science
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J. Anim Sci., doi: 10.2527/jas.2007-0016
©Copyright, 2007, The American Society of Animal Science

ARTICLE

Evaluation of the impact of errors in the measurement of backfat depth on the prediction of fat-free lean

A. P. Schinckel 1*, M. E. Einstein 1, K. Foster 2, B. A. Craig 3

1 Department of Animal Sciences, Purdue University, West Lafayette, IN 47907
2 Department of Agricultural Economics, Purdue University, West Lafayette, IN 47907
3 Department of Statistics, Purdue University, West Lafayette, IN 47907

* To whom correspondence should be addressed. E-mail: aschinck{at}purdue.edu.


  Abstract

The development of regression equations to predict carcass composition typically assumes that the independent variables, such as backfat depth, are measured without error. However, technological and operator-specific types of measurement errors do exist. To evaluate the impact of measurement error for backfat depth, Monte Carlo simulation was used to model carcass fat-free lean mass (FFLM) in pigs. In the simulation, FFLM was a linear function of carcass weight (CW) and actual backfat depth (ABFD). Carcass weight was assumed to be measured without error but measurement errors were generated such that the correlation (rBF) of the measured backfat depth (BFD) and ABFD ranged from 0.70 to 0.95. Two types of measurement errors were simulated: (1) constant variation that was additive to the variance of ABFD, and (2) variation proportional to the ABFD that was additive to the variance in ABFD. A total of 1000 replications of 1000 pigs were simulated. Within each type of measurement error, the absolute values of the regression coefficients and R2 values of the equations decreased as rBF decreased. The probability of the backfat depth squared (BFD2) being significant (P < 0.05) in the regression equation was increased when the measurement errors were proportional to ABFD. The occurrence of a significant BFD2 variable was 792 times out of 1000 replications when rBF = 0.95 and increased to 996 times out of 1000 when rBF = 0.85 for BFD's with type 2 measurement errors. The inclusion of a CW x BFD variable to the regression equations (P < 0.05) increased (270 to 423 times out of 1000) as rBF decreased from 0.85 to 0.70 for BFD's with type 2 errors. Equations developed from BFD's with measurement errors resulted in biased prediction of FFLM and changes in FFLM per unit change in BFD. The level and type of measurement errors that exist in the independent variables should be evaluated.

Key Words: Carcass composition, Measurement errors, Pigs, Prediction equations






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Copyright © 2007 by the American Society of Animal Science.