The data collection form (also referred to as a questionnaire, case report form or interview guide) is the focal point of any research project. It contains the data used to test the research hypotheses. If errors are made in translating the questions of interest into items on the form, or in coding those items, the answers sought might not be available. Designing an excellent data collection form may be more art than science. However, there are certain principles that, if followed, will generally result in an easy-to-use, efficient and reliable instrument for gathering and coding data.