calculating bmi

[Martin Imelda Borg]

So I am trying to create BMI classes according to the WHO classification.

My database currently has BMI, HEIGHT (CM), Weight (KG) stored as string variables




So I decided to

1. Encode and create BMI variable which I can work with and then convert into classes as per WHO..

The following code:




encode primarybmi, gen (NewBMI)




*Generating BMI groups*

gen BmiGroup = 0




replace BmiGroup = . if NewBMI ==.

replace BmiGroup = 1 if NewBMI <18.5

replace BmiGroup = 2 if NewBMI >=18.5 & NewBMI <=24.9

replace BmiGroup = 3 if NewBMI >=25.0 & NewBMI <=29.9

replace BmiGroup = 4 if NewBMI >=30.0 & NewBMI <=34.9

replace BmiGroup = 5 if NewBMI >=35.0 & NewBMI <=39.9

replace BmiGroup = 6 if NewBMI >=40 & !missing(NewBMI)




However, the problem I have values in the Bmigroup being incorrectly labelled as 6 when they don’t fall in the 6 category - they should for example be 4.




I don’t understand why this is happening.




I then tried to Calculate the BMI myself rather than use the database’s BMI so I tried this:




encode height, gen(NewHeight)

encode weight, gen(NewWeight)

generate Newbmi = NewWeight/ (NewHeight /100)^2




However, I have got values that do not make sense

eg. with




NewHeight: 173

NewWeight: 68

____

Newbmi: 285.66




This should read as 22.7




What am I doing wrong?

[Maarten Buis]

To quote the helpfile from encode:

Do not use encode if varname contains numbers that merely happen to be stored as strings; instead, use generate newvar = real(varname) or destring