What does a psephologist study

Deals with the study and scientific analysis of elections.
Psephology /sᵻˈfɒlədʒi/ (from Greek psephos ψῆφος, 'pebble', which the Greeks used as ballots) is a branch of political science which deals with the study and scientific analysis of elections.

Psephology uses historical precinct voting data, public opinion polls, campaign finance information and similar statistical data.

The term was coined in the United Kingdom in 1952 by the historian R. B. McCallum to describe the scientific analysis of past elections.

Read more...https://en.wikipedia.org/wiki/Psephology