# st: Patterns of longitudinal data

 From Dick Campbell To "statalist-hsphsun2.harvard.edu" Subject st: Patterns of longitudinal data Date Sat, 10 Aug 2002 08:24:01 -0500

Guillermo Cruces said:

I am working with panel data and I found the program xtpattern extremely useful.
<snip>
What I need now is to know how many contiguous observations there are, so for
instance:
1.1..1 would be zero
111111 would be six
111.11 would be (perhaps) three (the max).

The obvious thing would be to parse through the string generated by xtpattern...
but I couldn't find an elegant way around this p

xtpattern generates a string variable in the form 1.11.1 etc.
This can be interpreted as a binary number. Suppose there
are three observations maximum and we create the decimal
equivalent of the binary numbers resulting from xtpattern.
The fist position expands as 2**2, the second as 2**1
and the third as 2**0 (= 1). Thus for each pattern of observations
there is a unique decimal number,
Here is an example for four possible patterns.
111 = 7
11. = 6
1.1 = 5
1.. = 4

A neat characteristic of the decimal number is that
the higher the number of consecutive observations at the beginning of the
series the higher the decimal number. The second observation has a higher number than the third.
etc. You will also see that "consecutive observations always generate higher numbers
that non-consecutive, regardless of pattern.

=====================================
Richard T. Campbell
Professor of Sociology
Phone: 312/413-3759
Fax: 312/996-5104