correspondence

 a correspondence / to correspond / corresponding

A correspondence is a link between two things. This link may be because they match, because there’s a statistical relationship between them or because one of them leads to the other. It’s used a lot to compare or report on research. Correspondence can have another meaning – especially in business – which is a more formal way of saying letters and emails between people. So when someone returns to work they have to catch up with their correspondence.

Her research found little correspondence  between  investment and profitability.

The Greeks were the first to realise that the intervals between musical notes corresponded  to mathematical ratios.