Table 3.

Logistic multiple regressions of farm characteristics as predictors of PRRSV clinical disease signs (52 farms, IL, USA; 1997–1998)

Outcome variable

ABORT

INFERT

SOWDEATH

PWMORT

RESPNURS

RESPFIN

LONGTIME

Goodness-of-fit measuresa

G (P)

4.86 (0.088)

9.47 (0.024)

6.38 (0.041)

NA

18.16 (0.001)

NA

NA

HL (P)

0.36 (0.834)

0.03 (0.986)

5.67 (0.579)

NA

8.74 (0.365)

NA

NA

Predictor variableb

Intercept (P)

0.04 (0.903)

0.77 (0.162)

−2.0 (0.001)

NA

2.77 (0.984)

NA

NA

HERDSIZEc

NR

NR

R, S

NR

R, S

NR

NR

β (P)

–

–

0.06 (0.042)

–

0.18 (0.011)

–

–

aOR (95% CI)

–

–

1.06 (0.98–1.14)

–

1.20 (1.00–1.45)

–

–

NURSAIAO

R, S

R, S

R, S

NR

NR

NR

NR

β (P)

−0.85 (0.032)

−1.05 (0.015)

−1.15 (0.012)

–

–

–

–

aOR (95% CI)

0.43 (0.24–0.76)

0.35 (0.25–0.49)

0.32 (0.10–1.03)

–

–

–

–

FINAIAO

R

R

NR

NR

R, S

NR

NR

β (P)

0.78 (0.067)

1.15 (0.010)

–

–

−1.33 (0.002)

–

–

aOR (95% CI)

2.18 (1.28–3.69)

3.15 (2.31–4.29)

–

–

0.26 (0.09–0.76)

–

–

^aG=log likelihood ratio test for goodness of overall fit of the model; HL=Hosmer–Lemeshow residual test for goodness-of-fit of the logistic regression model.

^bNR=not retained in the final model; R=retained in the final model; S=significant at the 0.05 level; NA=not applicable (no variables retained in the final model); β=parameter estimate for each variable; aOR=adjusted odds ratio for each variable. Predictors were considered significant only if they were in the predicted direction and if their associated one-tailed P values were <0.05. P values given for significant variables are one-tailed; all other P values are 2-tailed. Neither CONFINE nor VACCINE was retained in any model.

^cAdjusted odds ratios for HERDSIZE are expressed as the risk associated with an increase in herd size of 1000 animals.