Tatapie, some Universities will tell you how many applicants per place. You get an idea of how competitive the course might be, though need to consider which will be top choice. Top Universities (for economics this will include LSE, UCL, Warwick, Durham and St Andrews) will be rejecting students with entry qualifications. An oft told story, but DS was predicted 4A* including FM but still received three rejections including Warwick. LSE, which he did get, had 13 applicants per place.
Which rankings are you looking at? If the Complete University Guide, then its worth looking at component parts. Average entry grade will give a sense of how competitive entry is. (Allow for the fact that many private and grammar schools allow student to sit four, and in DS' case, five A levels, even though the extra don't really help for University admissions.) Research quality relevant to some, especially those hoping to go on to post-grad.
Student satisfaction, well..... I have a theory that Bournemouth U bounces up and down the tables depending on how much beach weather there was. London Universities tend to do badly though some students prefer to be in the city. LSE students apparently took some pride in always being at the bottom of the satisfaction rankings and answered questionnaires accordingly. That said, it probably tells you something. The heavy weighting given to student satisfaction makes the Guardian rankings quite odd.
Then econometrics. It can be as hard as a University wants to make it. The main problem is that many students find it dry. I think there is a general problem with maths at University, in that as well as the ability you need the sort of character that is prepared to spend hours looking at problems and practising until the concept is embedded. Not for everyone.