How to merge two datasets by one variable?

[Lisa Spoelstra]

Dear all, I want to merge two datasets by age, for every age from 1-120 in my "age" dataset I have for example a different death rate, it looks like this;

age	death rate
1	..
2	..
3	..
4	..
5	..
6	..
...	..
119	..
120	..

In the other dataset for my population (the using dataset), I have a lot of observations and people who have the same age like this:

Age	Variable 1
1	..
1	..
1	..
1	..
5	..
5	..
...	..
80	..
80	..

I tried this:

merge m:1 age using "dta-files\populatie_def.dta"

However, I get the error:
''variable age does not uniquely identify observations in the
using data''

I understand that this is the case because in the using data there are more persons with the same age. But, how to solve this?

[Jorrit Gosens]

Youre merging the wrong way around.
Either do:

merge 1:m age using "dta-files\populatie_def.dta"

But åprobably better is to load the populatie_def.dta into memory, and then do

merge m:1 age using "dta-files\age.dta"

with the idea being that the master dataset (in memory) has many, and the 'using' dataset in a m:1 has only one observation for each value of age

[Lisa Spoelstra]

Thanks! It works.