Voting behaviour that is shaped by party policies and (usually) a calculation of personal self-interest.
Where issue voting takes place, voters place one issue above all others and cast their vote based on that issue. They judge a party or candidate by their position on the issue and choose the one that most closely reflects their own opinion. This can mean they vote for a candidate whose other policies would be to their detriment.
Elections in the UK are rarely dominated by one issue-although the health of the economy is consistently significant- but 2019 could be described a s the Brexit election.
Rational choice theory assumes that voters will make a rational, or logical, judgement based on what is in their own best interests. In an ideal version, voters will be fully informed about the various options and will choose the option that is best for them. By aggregating these views, the winning verdict will reflect what is best for society as a whole. The assumption here is that a voter will conduct a cost/benefit analysis of all options and make their choice accordingly.