Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.

# st: Compare rate of change in proportion with time in 2 groups

 From Quinn Leigh To statalist@hsphsun2.harvard.edu Subject st: Compare rate of change in proportion with time in 2 groups Date Thu, 2 Jun 2011 14:55:28 +1000

```Dear all,

I'm very new to STATA and have limited statistical knowledge. I have a
set of grouped data which looks like this

year   sex   Disease_A   Disease_B   Total
1991    1       10                1               11
1992    1       16                3               19
1993    1       20                9               29
1994    1       10                7               17
1995    1       15              13               28
1996    1       22              16               38
1991    2        3                2                 5
1992    2        5                0                 5
1993    2        5                0                 5
1994    2        7                1                 8
1995    2        9                2               11
1996    2        5                3                 8

The data shows that the total number of both Disease_A and Disease_B
have increased with time. Sex=1 (male) is more common in both
Disease_A and Disease_B. My question is, how do I find out whether the
proportion of male:female changed with time (eg. the proportion of
male is 60% in 1991 and increased to 70% in 1996), and if they have
changed, whether Disease_A and Disease_B have different rates of
change in proportion (eg. the proportion of male increased faster in
Disease_A compared to Disease_B, from 60% to 70% in disease_A compared
to from 70% to 75% in disease_B)?

I attempt to use blogit function (blogit Disease_A Total sex year) but
I'm not quite sure of the results because if a small p-value (eg.
0.03) for 'year' is obtained, would it be a result of increased number
of cases with time, not increased proportion?

Thanks you.

Regards,

Quinn
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/
```