Juan_Castro Marquez

event and depicts a decreasing likelihood of a scour outbreak as the calf ages in both GOS and
GAM experiments; nonetheless, per each unit increase in BP, while holding every other variable
constant and ignoring the intercepts, there is a further reduction in the probability of diarrhea in
the GOS study. In contrast, BP seemed to drive such probability upwards in the GAM study. For
instance, from 6 to 13 days of age, when diarrheal episodes appear to exacerbate, and at average
BP of 5.6 mg/dL, the estimated probability of a scour outbreak increased from 0.57 to 0.58 in the
GOS study; whereas, it went from 0.67 up to 0.72 in the GAM study.
Lastly, model 3 shows that calves with normal BW had lower odds (
) of
presenting diarrhea compared to underweight calves (i.e. BW < 40.7 kg). Moreover, BW
interacted with the linear component of age affecting the rate of increase of the odds of
presenting scours, but this interaction differed between studies as well. Compared to the GOS
study, the increase in the odds of a diarrheal episode was faster for calves in the GAM trial
( ). Figure 2.3b illustrates this in terms of probability.
Finally, none of the variables employed in the 3 models could lower the calf specific
variance below 0.7 (Table 2.2) even though they improved the fit of the model, indicating that
other unknown calf specific variables are responsible for the differences among calves. Yet, the
average intra calf correlation (Fitzmaurice et al., 2011) of the score measures for the 3 models
was ~ 0.14, indicating rather low variability among calves (14%); this is the proportion of total
unexplained variance attributed to variation among calves (i.e., clusters). The remaining 86% is
due to unidentified sources of variation at the repeated measure level; these are variables whose
values change from one day to the next for a given calf and that remain to be identified.
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