I've just read the Methodology page click the tab it says this.....
•Teaching — the learning environment (worth 30 per cent of the overall ranking score)
•Research — volume, income and reputation (worth 30 per cent)
•Citations — research influence (worth 30 per cent)
•Industry income — innovation (worth 2.5 per cent)
•International outlook — staff, students and research (worth 7.5 per cent).
It explains how they rate teaching, research etc
To paraphrase: The rankings are based on citations in well known journals I assume English language publications, research ie rich countries and teaching staff to student ratios on this point the methodology page states
As this measure serves as only a crude proxy - after all, you cannot judge the quality of the food in a restaurant by the number of waiters employed to serve it
Everyone loves rankings but understanding the methodology behind them is important