Adequacy of interval estimates of yield responses to ozone estimated from NCLAN data

Technical Report · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5979188

Somerville, M C; Dassle, K A; Rawlings, J O

Three methods of estimating confidence intervals for the parameters of Weibull nonlinear models are examined. These methods are based on linear approximation theory (Wald), the likelihood ratio test, and Clarke's (1987) procedures. Analyses are based on Weibull dose-response equations, developed from the National Crop Loss Assessment Network (NCLAN), that estimate yield as a function of ozone concentration. Comparisons among the three methods of confidence interval construction were also made for relative yield loss, a nonlinear function of the Weibull parameters. The results of these comparisons are considered along with the conclusions indicated using Clarke's measures of parameter-effects curvature and his seriousness criteria. Plots of the Wald and likelihood ration confidence intervals are shown for comparison. It is shown that in two cases the Wald confidence intervals are misleading, but in a third case they are entirely adequate. Clarke's methods identified the two cases where the linear approximation is inadequate and also showed whether his adjustment to the Wald would result in acceptable confidence intervals. The failure of the linear approximation appeared to be due to high variability and/or incomplete coverage of the response curve by the data. Comparisons of the Wald and likelihood ration confidence interval estimates for six other data sets showed the linear approximation to be adequate.

• Research Organization: North Carolina State Univ., Raleigh, NC (USA)
• OSTI ID: 5979188
• Report Number(s): PB-91-144832/XAB
• Country of Publication: United States
• Language: English

Related Subjects

560300* -- Chemicals Metabolism & Toxicology
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AIR POLLUTION
CROPS
DOSE-RESPONSE RELATIONSHIPS
ENVIRONMENTAL EFFECTS
MATHEMATICAL MODELS
OZONE
POLLUTION
PRODUCTIVITY
TOXICITY