Lesson 1.
Keep the secrets.
Lesson learned
The secret personal data becomes aggregated statistical data if there are 20 or more persons at each group.
How to
1.Count number of members of each group ( may use pivot table to count in multiple dimensions ( i.e. may be 30 women but only 10 women under age 45)
2.Use ranges or other groupings. Age groups, larger geographic notations
3.Use quartile or percentiles (QUARTILE , PERCENTILE.INC formulas in Excel ) to define reasonable ranges. At any data set exactly 1/4 of the observations in each quartile, so see what the quartiles values are and refine readable ranges nerby if you want 4 groups or see percentiles to fine-tuning ( define your number of equal groups then the whole is 100 ).
How I learned it
The very first thing I heard at my workplace as data manager, was about the privacy of data and that we can and should make statistics, models etc but never share the data itself.
One of my first things to do was to show some big picture of salaries in different organizational units.
I thought wow I will do it so private and nobody will know from the data I share any private information.
I carefully removed IDs, surnames and names... I thought that I'm OK...
But the case is that It was age info in my data, and that already made the data too transparent to people who know to read it...
Good that I get the angry calls fast and recalled my mail at outlook...