“The question protocol”, as suggested by Richard Rutter, is a handy heuristic to evaluate the data fields of a form:
When designing a form, you can ensure you are gathering only pertinent information by always invoking the question protocol. The question protocol forces you – and your organization – to ask yourselves why you are requesting a piece of information from a customer. Getting to the bottom of why you’re asking a question means determining precisely how you will be using the answer, if at all.[…]