feruz77 wrote:
The average age of university presidents in a large sample of universities is 62. The average age of university presidents in those same universities 25 years ago was approximately eight years younger. On the basis of those data, it can be concluded that university presidents, including those at online universities, in general tend to be older now.
Which of the following casts the most doubt on the conclusion drawn above?
(A) The dates when the university presidents assumed their current positions have not been specified.
(B) No information is given concerning the average number of years that university presidents remain in office.
(C) The information is based only on universities that have been operating for at least 25 years.
(D) Information concerning the exact number of universities in the sample has not been given.
(E) None of the answers provided cast doubt on the conclusion drawn above.
OFFICIAL EXPLANATION:
From a study of the average ages of university presidents in ‘a large sample of universities’ a general conclusion has been arrived at, which is then presumed to be applicable to all universities.
We have been asked to identify that choice which would cast the most doubt on this conclusion. Since the question asks for the answer that casts the most doubt, one of the answers must be chosen and answer (E) none of the above is incorrect.
We should therefore look for that statement which implies that the sample universities studied did not represent the majority of universities in some important respect, and that it is therefore unscientific to arrive at a general conclusion based on this unrepresentative sample. (A ‘large sample’ may still constitute a minority of the total number of companies.)
The phrase ‘in those same universities 20 years ago’ in the third line of the passage implies that the companies taken up for the sample study were limited to those which have been operating for more than 20 years. If a many of the existing universities (including online universities) are, in fact, less than 20 years old, the phenomenon prevailing in the older universities cannot be inferred as being applicable generally to all universities. It is quite likely that the average age of the university presidents of newer universities is much less than 57.
It is (C) which implies this, and is the answer. _________________