I am trying to draw a common pre-trend graph for a diff-in-diff design. My treatment group is made of one only state, while the control group is made of three states. The data are a panel so that I have obseervations for each unit (state) over the same period of time. I'll post here a portion of it

Code:
 state  year   cases     pop
ACT    1971     35     151169  
ACT    1972     57     159792
ACT    1973     35     173306
ACT    1974     34     186241
ACT    1975     67     199007
ACT    1976     44     207740
ACT    1977     145    213688
ACT    1978     180    217981
ACT    1979     280    220797
ACT    1980     269    224291
NSW    1971    3943    4725503
NSW    1972    3698    4795106
NSW    1973    3356    4841898
NSW    1974    3606    4894053
NSW    1975    3517    4932016
NSW    1976    3535    4959588
NSW    1977    3807    5001888
NSW    1978    4180    5053790
NSW    1979    3656    5111130
NSW    1980    3643    5171527
NSW    1981    3841    5234889
NT     1971    412     85735
NT     1972    404     92081
NT     1973    524     97127
NT     1974    563     102924
NT     1975    494     92869
NT     1976    515     98228
NT     1977    560     103938
NT     1978    719     109980
NT     1979    911     114149
NT     1980    722     118245
NT     1981    970     122616
Qld    1971    1852    1851485
Qld    1972    2039    1898478
Qld    1973    2192    1951951
Qld    1974    1952    2008340
Qld    1975    1718    2051362
Qld    1976    1492    2092375
Qld    1977    1678    2129839
Qld    1978    2107    2172047
Qld    1979    1695    2214771
Qld    1980    1838    2265935
Qld    1981    1353    2345208
Now what I would like to plot are just two lines, one for the treated group and one for the control group (three of those state in aggregate, e.g. NSW, NT and Qld). What I need to plot is the ratio "cases/pop".

My code by now is

Code:
twoway (line log_GON year if treated == 1, lcolor(red) xline(1995)) (line log_GON year if treated== 0, lcolor(blue))
where treated variable is equal to 1 for state ACT and equal to 0 for state NSW, NT and Qld. But the result is a plot with 4 lines, one for each state instead of one for the treated group and one for the control group in aggregate

What is the more meaningful way of doing it? Should I manually aggregate the data (i.e. summing cases and pop by year and create a new "control" state) or is there a easier way of doing it?