Prospective studies?

What is a prospective study exactly? I'm reviewing a journal article about a prospective study following some 60,000 women nurses for 4 years with the use of questionnaires in regards to dietary intakes and the effects on blood pressure...... any ideas on how I could explain the type of study this is?

prospective studies define their research group and the criteria for which they are looking before the study actually begins. so for this one, they chose the nurses and decided what they were going to ask them before it started. in a retrospective study, they would have as the nurses to report what they had been eating for the past year and then looked at their medical charts for the past year and looked for any changes. so, prospective = looking forward. retrospective = looking back.

I agree with the person that answered before me. The study is a prospective cohort study. The study have a risk factor (dietary intakes) and how the dietary intake will affect the BP of the patients (disease). In other words, they are trying to assess wheher the risk factor increase the likelihood of disease (effects in blood pressure).