How to compute the OR for 30 or 10 unit increase of a continuous predictor

[Fouzi Rafik]

Hello everyone,
I would like to ask a question about computing the OR in logistic regression analysis.
I am running a logistic regression model to predict mortality (the outcome), using categorical and continuous variables. In my continuous variables, I have "time delay from diagnosis" variable which is expressed in minutes. When I run the logistic regression, I get OR for every increase in 1 unit of time, but I would like to get the OR for 30 min delay in time, because 1 minute delay is not meaningful in the context of my analysis.
I think I will need to generate a new variable, but I don't know what’s the correct command for that.
Same question for age (years, continuous variable) if I want to compute the OR per 10 years increase and not 1 year.
Thank you for your help

[Rich Goldstein]

gen newvar=oldvar/30

or by 10 or ...

[Fouzi Rafik]

Thanks Rich for your reply,
Does it make sense to use this code as well:
gen newvar= (oldvar + 30)

[Rich Goldstein]

no, it does not; the unit will still be exactly as it was before adding the 30 which is not what you asked for in #1

[Fouzi Rafik]

Thank you.

[Richard Williams]

You can also do things like

webuse nhanes2f, clear
logit diabetes height weight, or
di 1.03062^30

Or, to be really precise,

di exp(_b[weight]) ^ 30

[Bruce Weaver]

If you use -lincom-, you'll SEs and CIs too.

clear
webuse nhanes2f
logit diabetes height weight
// Get coefficient for weight via -lincom-
lincom weight

// Let wt30 = weight/30
generate wt30 = weight/30
logit diabetes height wt30
lincom wt30

// Estimate the original model again, and then
// use lincom to get the coefficient for wt30
quietly logit diabetes height weight
lincom 30*weight
// Add eform option to lincom to get odds ratios
// OR for a 1 kg increase in weight
lincom weight, eform
// OR for a 10 kg increase in weight
lincom 10*weight, eform
// OR for a 20 kg increase in weight
lincom 20*weight, eform
// OR for a 30 kg increase in weight
lincom 30*weight, eform