Here; an excerpt:

[I]f the rankings are to be used just to evaluate the quantity or quality  of research, they are frankly of little use. They are dominated by the survey of  academic opinion, which is not of professional quality.

There are several ways in which people can take part in the survey. They can  be nominated by a university, they can sign  up  themselves, they can be recommended by a previous respondent or they can be  asked because they have subscribed to an academic journal or an online database.

Apart from checking that they have a valid academic e-mail address, it is not  clear whether QS makes any attempt to check whether the survey respondents are  really qualified to make any judgements about research.

The result is that the academic survey and also the employer survey have  produced results that do not appear plausible.

In recent years, there have been some odd results from QS surveys. My  personal favorite is the New York University Tisch School of the Arts, which set  up a branch in Singapore in 2007 and graduated its first batch of students from  a three-year Film course in 2010.

In the QS Asian University Rankings of that year, the Singapore branch got  zero for the other criteria (presumably the school did not submit data) but it  was ranked 149th in Asia for academic reputation and 114th for employer  reputation.

Not bad for a school that had yet to produce any graduates when the survey  was taken early in the year….

Another example is from Saudi Arabia, where King Fahd University of Petroleum  and Minerals was apparently top for history, even though it does not have a  history department or indeed anything where you might expect to find a  historian.