Preparing the Data for Analysis

Before restructuring the data, you will need to create two ancillary variables to help with the restructuring.

1. To compute a new variable, from the menus choose:

   Transform > Compute Variable...

   

2. In the Compute Variable dialog, type start_time2 as the target variable.
3. Type time1 as the numeric expression.
4. Click OK.
5. Recall the Compute Variable dialog box.
6. Type start_time3 as the target variable.
7. Type time2 as the numeric expression.
8. Click OK.
9. To restructure the data from variables to cases, from the menus choose:

   Data > Restructure...

   

10. In the Welcome step, make sure Restructure selected variables into cases is selected.
11. Click Next.

    

12. In step 2, select More than one variable group to restructure.
13. Type 6 as the number of groups.
14. Click Next.

    

15. In the Case Group Identification group, select Use selected variable and select Patient ID [patid] as the subject identifier.
16. Type event as the first target variable.
17. Select First event post-attack [event1], Second event post-attack [event2], and Third event post-attack [event3] as variables to be transposed.
18. Select trans2 from the target variable list.

    

19. Type start_time as the target variable.
20. Select Length of stay for rehabilitation [los_rehab], start_time2, and start_time3 as variables to be transposed. Time to first event post-attack [time1] and Time to second event post-attack [time2] will be used to create the end times, and each variable can only appear in one list of variables to be transposed, thus start_time2 and start_time3 were necessary.
21. Select trans3 from the target variable list.

    

22. Type time_to_event as the target variable.
23. Select Time to first event post-attack [time1], Time to second event post-attack [time2], and Time to third event post-attack [time3] as variables to be transposed.
24. Select trans4 from the target variable list.

    

25. Type mi as the target variable.
26. Select History of myocardial infarction [mi], History of myocardial infarction [mi1], and History of myocardial infarction [mi2] as variables to be transposed.
27. Select trans5 from the target variable list.

    

28. Type is as the target variable.
29. Select History of ischemic stroke [is], History of ischemic stroke [is1], and History of ischemic stroke [is2] as variables to be transposed.
30. Select trans6 from the target variable list.

    

31. Type hs as the target variable.
32. Select History of hemorrhagic stroke [hs], History of hemorrhagic stroke [hs1], and History of hemorrhagic stroke [hs2] as variables to be transposed.
33. Click Next, then click Next in the Create Index Variables step.

    

34. In step 5, type event_index as the name of the index variable and type Event index as the variable label.
35. Click Next.

    

36. In step 6, make sure Keep and treat as fixed variable(s) is selected.
37. Click Finish.

    Table 1. Restructured data

    event_index	event	start_time	time_to_event	mi	is	hs
    1	0	3	1500	0	1	0
    2	-4	1500	-4	-4	-4	-4
    3	-4	.	-4	-4	-4	-4
    1	1	33	1311	0	1	0
    2	4	1311	1325	1	1	0
    3	-3	1325	-3	-3	-3	-3
    1	4	12	1098	1	1	0
    2	-3	1098	-3	-3	-3	-3
    3	-3	.	-3	-3	-3	-3

    The restructured data contains three cases for every patient; however, many patients experienced fewer than three events, so there are many cases with negative (missing) values for event. You can simply filter these from the dataset.

38. To filter these cases, from the menus choose:

    Data > Select Cases...

    

39. In the Select Cases dialog, select If condition is satisfied.
40. Click If.

    

41. In the Select Cases If dialog, type event >= 0 as the conditional expression.
42. Click Continue.
43. In the Select Cases dialog, select Delete unselected cases.
44. Click OK.

Next