Research that generates numerical data or data that can be converted into numbers. An example is research using clinical trials. Another example is the national Census, which counts people and households. It might involve questions like: 'How many people visit their GP each year?'; or 'What proportion of children have had this vaccine?'.

Quantitative and qualitative research are contrasting methodologies, based upon different epistemiological positions: qualitative research has its routes in interpretivism, which assumes that there is no “true reality” that exists independently from observation but that all reality is in fact socially constructed (subjectively interpreted) and therefore fluid. This position is in contrast to the positivist paradigm, within which quantitative research is usually based, which holds that there is a single, observable, and measurable reality that can be quantified and objectively interpreted. Broadly speaking, qualitative research tends to answer the “why?” and “how?” questions surrounding public health topics, in contrast to quantitative methodologies which tend to focus on epidemiological estimates of prevalence and strength of associations between variables. (Healthknowledge epidemiology)

Quantitative data: Observations that are numerical.

See also, qualitative research