Question 4: What do they mean by the odds ratio per quartile?
Usually we would get the odds ratio per unit of the measurement. What these authors have done is to recode the variable as 1 if below the first quartile, 2 if between the first and second, 3 if between the second and third, and 4 if above the third quartile. They have then used this variable as the predictor. The odds ratio estimate is then the odds ratio for a difference in house dust mite exposure from one quarter of the scale to the next. Personally, I donít like this idea much.
I warned you that this was really tough!
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