If/Then/Missing Statements

[chester2018]

Hi! 

I'm having trouble with my If/Then/Missing statements. For this example, I'm making BMI categories, but my new variable keeps making my missing values into one of the categories. I'm trying to get if bmi_v1 > 25, then iBMI_v1 = 100 and so on. There are missing values for bmi_v1, but the iBMI puts the missing values as "100" instead of ".".

data patient.guidelines;
	set  patient.health;
	if (bmi_v1) lt 25 then iBMI_v1 = 100;
	else if (bmi_v1) lt 30 then iBMI_v1 = 70;
	else if (bmi_v1) lt 35 then iBMI_v1 = 30;
	else if (bmi_v1) lt 40 then iBMI_v1 = 15;
	else if (bmi_v1) ge 40 then iBMI_v1 = 0;
	else iBMI_v1 = .;
run;

[Tom · Accepted solution]

Because that is what you told it to do.  Comparison operators, like < , treat missing values as less than any actual number.

if missing(bmi_v1) then iBMI_v1 = .;
else if (bmi_v1) lt 25 then iBMI_v1 = 100;
...

[ballardw]

Or

if 0 lt (bmi_v1) lt 25 then iBMI_v1 = 100;

[webart999ARM]

One way to fix this problem is to include an additional condition to check for missing values in the if statement. In SAS, missing values are represented by a dot (.), so you can add a condition to check if the value of bmi_v1 is equal to . and assign the missing value to iBMI_v1 in that case.

Here is an example of how you can modify your code to handle missing values:

data patient.guidelines;
	set  patient.health;
	if bmi_v1 = . then iBMI_v1 = .;
	else if (bmi_v1) lt 25 then iBMI_v1 = 100;
	else if (bmi_v1) lt 30 then iBMI_v1 = 70;
	else if (bmi_v1) lt 35 then iBMI_v1 = 30;
	else if (bmi_v1) lt 40 then iBMI_v1 = 15;
	else if (bmi_v1) ge 40 then iBMI_v1 = 0;
run;

In the code above, the first if statement checks if the value of bmi_v1 is equal to . and assigns the missing value to iBMI_v1 if that is the case. This ensures that any missing values in bmi_v1 will be preserved in iBMI_v1 and not assigned to one of the categories.