Research methodologies can be quantitative (for example, measuring the number of times someone does something under certain conditions) or qualitative (for example, asking people how they feel about a certain situation). Ideally, comprehensive research should try to incorporate both qualitative and quantitative methodologies but this is not always possible, usually due to time and financial constraints.
Research methodologies are generally used in academic research to test hypotheses or theories. A good design should ensure the research is valid, i.e. It clearly tests the hypothesis and not extraneous variables, and that the research is reliable, i.e. It yields consistent results every time.
Part of the research methodology is concerned with the how the research is conducted. This is called the study design and typically involves research conducted using questionnaires, interviews, observation and/or experiments.
The term research methodology, also referred to as research methods, usually encompasses the procedures followed to analyze and interpret the data gathered. These often use a range of sophisticated statistical analyses of the data to identify correlations or statistical significance in the results.
Objective, representative research can be difficult to conduct because tests can normally only be conducted on a small sample (e.g. You cannot test a drug on every person in the world so a sample needs to be used in research). This means that researchers need to have a very detailed understanding of the types and limitations of research methodologies which they are using.