Questionaires

Good for gathering information from a large number of people

Interviews

Good for getting the viewpoint of key users and management.

Examining documents

Good for understanding key data and how it flows

Observations

Good for understanding how people actually use the current system and any inefficiencies or problems that may occur.

Questionaires

Poor for analysing open questions and opinions

Interviews

Can be vulnerable to internal politics and agendas

Examining documents

Over-the-shoulder shadowing can affect the way people actually work. Video cameras can be difficult to set up.

Observations

Need to observe the relevant key people who may not be available in the project time.