I'd be too happy, if someone could post a code snippet, which explains how to compute mean and variance of a set of records, which contain frequencies?
Suppose we have records like (FORMAT F)
- GroupA, 6 x Grade 1, 5 x Grade 2, 10 x Grade 3 - GroupB, 2 x Grade 1, 7 x Grade 2, 18 x Grade 3 - GroupA, 23 x Grade 1, 5 x Grade 2, 1 x Grade 3 - GroupA, 10 x Grade 1, 15 x Grade 2, 12 x Grade 3
Goal: Compute for each Group's mean and variance of grades using SPSS syntax.
Using SPS, processing cases (FORMAT C) would be simple (as colleagues told me):
# Record number 1 (line 1 of the above data) GroupA, Grade 1 ... 6 times GroupA, Grade 1 GroupA, Grade 2 ... 5 times GroupA, Grade 2 GroupA, Grade 3 ... 10 times GroupA, Grade 3 # Record number 2 (line 2 of the above data) GroupB, Grade 1 GroupB, Grade 1 GroupB, Grade 2 ... 78 times GroupB, Grade 7 ... and so on
Unfortunately, we don't have cases of FORMAT C, but already aggregated data as in FORMAT F.
I probably should add this:
I implemented a solution, which uses (user entered) FORMAT F data using PHP/SQL: The PHP program constructs an SQL query, which computes the mean, the variance and the standard deviation of each Group.
I even tested the solution using well-known sample data. The results are identical. Thus I'm sure the solution is correct.
Since the computed statistical properties are sensible, I'd like to get a verification using a standard statistical package using the real FORMAT F data (not the test case data).
My colleague is going to use SPSS.