Volume 15, Number 5—May 2009
A Case–Control Study on the Origin of Atypical Scrapie in Sheep, France
|Variable||Coefficient (β)||Standard error (β)||p value†|
|Intercept||−3.03||0.37||7 × 10–16|
|Level of genetic risk‡||0.97||0.13||1 × 10–13|
|No. animals tested during 2002–2006||0.03||0.01||5 × 10–5|
|Sheep dairy farm||2.52||0.96||8 × 10–3|
|Corn silage in C0||−1.48||0.68||0.03|
|Vitamin and mineral supplements in C0||−0.40||0.40||0.31|
|Interaction term between sheep dairy farm and vitamin and mineral supplements in C0||−1.99||1.09||0.07|
*Genetic risk from multiple imputation parameters was estimated by the method of Little and Rubin (27). C0, birth cohort assuming that in each flock all animals born during the same birth campaign (defined from July 1 of year n – 1 to June 30 of year n) shared the same exposure.
†By Wald test.
‡Because the variable is ordinal, the odds ratio (OR) for a given level of genetic risk is the exponential of the coded level (see Table 1) multiplied by the estimated coefficient β. The ORs for groups 2–5 are 2.6, 7.0, 18.4, and 48.4, respectively.