Citation Counts and Influence and Tenure

Citation counts are quite unreliable, since they can be jiggered (you get credit for papers with your famous professor, having worked in his lab or project, but you really don't want to count those citations unless you did most of the work). But at the extremes, they may well be useful.  As for influence in the field, for assistant professors, letters are likely to be more informative. You’d need to award tenure at 9 years, rather than 6, to have good data for citations that would be worth attending to. Many fields have long gestation times.

But letters have their own problems, and only 1/3 at best really tell you what you would want to know about quality and influence, and again letters too may not be reliable even from strong scholars. But if you have several, they are likely to reveal the problems among them and so as a whole they are quite informative.

For Assoc to Full, the citation data is likely to be helpful. Again, it can be jiggered. Letters are still the best information, with the proviso that very high or low citation counts are flags.  h-indexes are popular with scientists, and they check them weekly in some cases. Warshel of recent Nobel Prize in Chemistry is one who said he did so.

As for whether papers are influential in policy, wow! It helps to have a stream of papers by many authors. Single papers, like "broken windows," may appeal to prejudices and so be influential, but even there others took up the challenge. In general single papers are quite unreliable unless explored by many folks in follow-up studies. And there is a lag between paper and influence, many years often, in part because interests that do not want the paper's ideas to dominate will work against that, and may well generate counter evidence. Think of tobacco use and decades between good evidence and changes in policy.

It also helps to do lecturing, testifying, and lots of people-work.