Dear friend,
To settle your query, let me put it this way. Shape of a curve depends on the how to assign the percentage to various categories. For example, consider the following percentage:
Excellent: - top 10% of the total strength
Very Good: - next 20
Good: - next 40%
Average: - next 20% and
Poor: - next 10%
In the Forced Distribution, the persons are forcibly fitted in some of the category. When you draw a map, you get a "Bell Curve". However, if you assign 20% to all the categorise, obviously bell shape will get converted into a straight line.
Thanks,
Dinesh Divekar