Dear all,

I have a four-wave panel data and I am looking for a way to identify missing values of age in the next periods. For example, waves 1 and 2 may have information on age but such information is missing in waves 3 and 4. After that, I want to fill the missing values in the next step. This can be done using the fact that the survey is conducted every two years. Any help is much appreciated.

Thank you.

Data
Code:
clear
input int id float(year age)
 1 2007 .
 1 2009 64
 1 2011 66
 1 2013 69
 2 2009 77
 2 2011 79
 2 2013  .
 3 2009 60
 3 2011 62
 5 2007 52
 5 2009 .
 5 2011 57
 5 2013 59
 6 2009 67
 6 2011 69
 6 2013 72
 8 2009 56
 8 2011 58
 8 2013 61
 9 2009 66
 9 2011 68
 9 2013 70
13 2009 70
13 2011 72
13 2013 74
15 2007 57
15 2009 59
15 2011 .
15 2013 64
16 2007 58
16 2009 61
16 2011 63
16 2013 65
17 2009 72
17 2011 74
17 2013  .
18 2009 60
18 2011 62
18 2013 64
19 2007 .
19 2009 73
19 2011 75
19 2013 78
20 2009 68
20 2011 70
21 2009 70
21 2011 72
21 2013 74
22 2007 .
22 2009 67
22 2011 69
22 2013  .
25 2007 57
25 2009 59
25 2011 61
25 2013 64
26 2009 66
26 2011 68
26 2013  .
27 2007 73
27 2009 75
27 2011 77
27 2013 80
29 2009 67
29 2011 69
29 2013  .
30 2009 .
30 2011 .
30 2013 61
31 2009 54
31 2011 56
31 2013 58
34 2009 72
34 2011 74
36 2007 60
36 2009 62
36 2011 64
38 2009 69
38 2011 71
38 2013 74
39 2009 71
39 2011 73
42 2009 61
42 2011 63
42 2013 65
43 2007 59
43 2009 61
43 2011 63
43 2013 66
45 2007 51
45 2009 54
45 2011 56
45 2013 58
46 2009 57
46 2011 59
46 2013  .
47 2007 73
47 2009 75
47 2011 77
47 2013 80
end