Writing a formula in which stata chooses a value or 1

[Vilma Antonov]

Hi!

I'm trying to use this formula to calculate eGFR: eGFR = 142*min(standardized Scr/K, 1)^α *max(standardized Scr/K, 1)^-1.200 *0.9938Age *1.012 [if female]
Scr= creatinine, e.g. creatinine=2.4.

In this formula, the min(standardized Scr/K, 1) means that you either choose the creatinine value divided by kappa, OR 1. The same goes for the max-one.

I'm looking for advice on how to write the command so Stata realizes this. Grateful for any help!

[Vilma Antonov]

I realised it might be hard to understand from my explanation: if the Scr/K is less than 1, it should choose that value. otherwise it should choose 1. The same goes for the maximum; if the Scr/K is larger than 1, it should choose that. Otherwise it should choose 1.

[Hemanshu Kumar]

I'm not sure I follow what the problem is.

min() and max() are both functions available in Stata. See e.g.

help min()

[Vilma Antonov]

My problem is that i dont know how to write “Scr/k if less than 1, otherwise 1” in the equation.

[Hemanshu Kumar]

This is how the min() function works:

. scalar Scr = 5
. scalar K = 10
. dis min(Scr/K,1)
.5
. scalar K = 2
. dis min(Scr/K,1)
1

[Vilma Antonov]

Thank you Hemanshu! I hade a typo making it not work. Thanks a lot!