Odds ratios lower than 1 for continous variable

didye

New Member
#1
Lets says you want to check the effect of age on a specific event.

In the univariate model : event = age, the odds is significantly lower than 1 which seems to show a 'protective impact' of age on this event (age increase -> probablity of event decrease)

However, after checking, average of age is significantly higher in peole who had the event than in people who didn't have the event.

How is it possible ??

Thanks for your help
 

Jake

Cookie Scientist
#2
Make sure your model is modeling the probability of the event occurring (event=1) rather than not occurring (event=0). Some programs such as SAS do the latter by default, which will reverse the signs of the odds ratios.
 

didye

New Member
#4
Thansk you for your help!
In the logisitic model of SAS (proc logistic), you have to add DESCENDING in aim to model the propability to have the value 1 if the event is coded 0/1