- #1
lavoisier
- 177
- 24
Hello,
I remember an example of application of the logistic regression to medicine / epidemiology, which said (more or less) that the probability of a person having miocardial infarction was related to some variables such as age, cholesterol level, etc, and the equation included the various 'thresholds' for each of these variables.
Something like: c0 + cage (age - 50) + cchol (chol - 200) + ...
This was the x in the logistic formula P=1/(1+e-x).
If the coefficients are all positive, it follows that when age > 50 and chol > 200, a positive contribution is given to x by these two variables, which makes e-x smaller, and P closer to 1.
Now my question is, how did they find the thresholds (50 and 200) for age and chol?
If I had data on age, cholesterol, etc, vs presence/absence of the disease, and ran a logistic regression, I think I would get something like this:
x = a0 + aage age + achol chol + ...
I.e. I would only know that age and chol increase P, but not 'when' someone should start to worry about their age and cholesterol.
Am I completely off the mark here, or is there a technique to calculate these thresholds from the data?
Thanks!
L
I remember an example of application of the logistic regression to medicine / epidemiology, which said (more or less) that the probability of a person having miocardial infarction was related to some variables such as age, cholesterol level, etc, and the equation included the various 'thresholds' for each of these variables.
Something like: c0 + cage (age - 50) + cchol (chol - 200) + ...
This was the x in the logistic formula P=1/(1+e-x).
If the coefficients are all positive, it follows that when age > 50 and chol > 200, a positive contribution is given to x by these two variables, which makes e-x smaller, and P closer to 1.
Now my question is, how did they find the thresholds (50 and 200) for age and chol?
If I had data on age, cholesterol, etc, vs presence/absence of the disease, and ran a logistic regression, I think I would get something like this:
x = a0 + aage age + achol chol + ...
I.e. I would only know that age and chol increase P, but not 'when' someone should start to worry about their age and cholesterol.
Am I completely off the mark here, or is there a technique to calculate these thresholds from the data?
Thanks!
L