Quantitative and Qualitative Data

Some methods provide data which are quantitative and some methods data which are qualitative.  Quantitative methods are those which focus on numbers and frequencies rather than on meaning and experience.  Quantitative methods (e.g. experiments, questionnaires and psychometric tests) provide information which is easy to analyse statistically and fairly reliable.  Quantitative methods are associated with the scientific and experimental approach and are criticised for not providing an in depth description.

Qualitative methods are ways of collecting data which are concerned with describing meaning, rather than with drawing statistical inferences.  What qualitative methods (e.g. case studies and interviews) lose on reliability they gain in terms of validity.  They provide a more in depth and rich description.

Quantitative methods have come under considerable criticism.  In modern research, most psychologists tend to adopt a combination of qualitative and quantitative approaches, which allow statistically reliable information obtained from numerical measurement to be backed up by and enriched by information about the research participants' explanations.

You will find that many of the core studies do collect both types of data.