You want to estimate an important quantity. You compute an exact number purporting to estimate it. You compute another exact number purporting to estimate it. The two numbers differ significantly. The only logical conclusion is that these estimates are less exact than they seem.

This clearly seems to be the case with the notion of “impact” as quantified by different  metrics that purport to estimate the same quantity from the same data:


Perhaps a good antidote to innumeracy can be playing with data interactively. So, you can search these data interactively and find for yourself how different metrics of impact may differ by over 300 % !