I am working on a paper about discrimination in the labour market. I have three variables (among many others): one is race (black/white), the other is callback and the third is advertisement. Race and callback are dummies, the ad variable assigns a number to each job advertisement from 1 to 1200

the dataset is like this

race call ad
b 0 1
w 0 1
b 0 1
w 0 1

Which means that for ad 1, nobody got called back

then I have

race call ad
w 0 216
b 1 216
b 1 216
w 0 216

which means that for ad 216, 2 African-Americans got called back and 0 Whites

or


race call ad
b 0 376
w 1 376
b 0 376
w 1 376

which means that for ad 376 2 whites got called back and no African-Americans

I need to to know the percentage of ads that favored african americans (like ad 216) or they treates the candidates equally (like ad 1) or they favored whites (like other ads where 1 white got called back and no african americans) so I need to discern the advertisement variable to know how many ads called 0 whites and 0 blacks or 1 black and 1 white or 2 whites and 0 blacks and so on.

I am relatively new to Stata so I've tried to use the summarize command, unsuccessfully

sum ad if race=="w" & call==0 & race=="b" & call==1 says "no observations"

I tried to use tabulate race call adid, row and it says "too many variables specified" so I switched to bysort ad: summarize race call yet I got no results.