Table 2.

Data from a hypothetical observational study of 12 people

Person/clone	durA	Aspirin at start of first year	Dead at end of first year	Aspirin at start of second year	Dead at end of second year	Inverse probability weight
1	0	No	No	No	No	1
2	0	No	No	No	Yes	1
3	0	No	No	No	Yes	1
4	0	No	Yes	-	Yes	1
5a	1	Yes	No	No	No	2
6a	1	Yes	No	No	Yes	2
7a	1	Yes	No	No	Yes	2
8a	1	Yes	Yes	-	Yes	1
9a	1	Yes	No	Yes	Censored	0
10a	1	Yes	No	Yes	Censored	0
11a	1	Yes	No	Yes	Censored	0
12a	1	Yes	Yes	-	Yes	1
5b	2	Yes	No	No	Censored	0
6b	2	Yes	No	No	Censored	0
7b	2	Yes	No	No	Censored	0
8b	2	Yes	Yes	-	Yes	1
9b	2	Yes	No	Yes	No	2
10b	2	Yes	No	Yes	Yes	2
11b	2	Yes	No	Yes	Yes	2
12b	2	Yes	Yes	-	Yes	1