[arjie]

The Herfindahl-Hirschman Index is a measure of the concentration of a market based on the market-share of the firms participating in it. Very much like the Simpson's index that tells you the probability of two organisms in a place being of the same type when randomly drawn.

It's just \sum_i^n h_{i}^2 sum of squares of market-share.

Enjoyed that. Thanks for the discovery.

[zombot]

Why does the `i` after `h_` need a curly but not after `\sum_`?

A pity that HN can't render TeX or MathJax or whatever.

[tempfile]

It doesn't. The rule for TeX is that single-character tokens don't need braces. I assume this is just an artefact of their particular muscle memory.

You can test it here, if you like: https://www.mathjax.org/#demo

[dfee]

HHI and Simpsons are neat new finds.

There's also this other variant of the Simpson's Index: https://www.thesimpsonsindex.com/

[scarab92]

Payment processor margins are already very high, especially considering they are basically low-tech utilities.

If the US had functioning antitrust laws it would be looking at their margins and be considering whether to break up some of the existing players, not considering when allow even more mergers.

[Ey7NFZ3P0nzAe]

https://en.wikipedia.org/wiki/Diversity_index