Test-preparation organizations like Kaplan, Princeton Review, etc. often advertise their services by claiming that students gain an average of 100 or more points on the Scholastic Achievement Test (SAT). Do you think that taking one of those classes would give a test taker 100 extra points? Why might an average of 100 points be a biased estimate?

 

The claim that on an average 100 or more points are gained by taking the classes, is definitely a biased claim. It is made just to attract more and more students. No doubt these services are really good and students who join them have a higher chance of scoring better. But claiming an exact 100 more score on an average is very much biased.

The reasons are as follows:

1. Firstly the increase in score doesn't merely depend on the organization joined by them. This is not the only factor that affects the increase in score.
2. Secondly, sincerity of the student, his IQ, practice all are alos some of the imperative contributors to the gain in score.
3. Thirdly, not all students are same in their initial performance level, there are students who are weak in subject , for them the gain may be just 20-30 points, there are some students are average in their performance for them the average improvement may be around 50 to 70 points, and then there are some intelligent lot of students who with the appropriate guidance of the test prep organizations are able to improve their scores drastically by more than 100 points.

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Conclusion:

Thus we can observe that the average improvement has many predictor variables, plus it is too biased a statement to say that the average improvement is by 100 point, since for different students the average is different