I can easily do systematic sampling from the equal interval sample like 1,2,3,4,5,6,7,8,9,........ But I didn't select through systematic random sampling form the unequal interval.
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Unit Mi Ti Range SelectionNumber
1 3 9 1-9
2 1 12 10-12
3 11 45 13-45 17
4 6 63 46-63 47
5 4 75 64-75
6 2 81 76-81 77
7 3 90 82-90

From the above data how can I select the number through the systematic random sampling in stata.
From the Ti (Cumulative frequency) have to chose three sample through systematic random.
How it is possible. Advanced Thank.