There are two types of market research: quantitative and qualitative.
Quantitative research yields information about the number of people who fit certain criteria. An example of quantitative research is conducting a survey to determine the percentage of people who have bought a competitor's product.
Qualitative research, on the other hand, yields non-numeric information, such as an account of a particular customer's situation and problems. A product manager might determine the customer's situation and problems by conducting a one-on-one interview. Since it is not directly quantifiable, the information from qualitative research is not always "scientific".
In an upcoming entry, I will examine why both types of research are important.