What are the main distinctions between qualitative and quantitative approaches to measurement?

•   The first distinction is timing. Quantitative researchers think about variables and convert them into specific actions during a planning stage that occurs before and is separate from gathering or analyzing data. Measurement for qualitative researchers occurs during the data collection process.
•   The second distinction involves the data themselves. Quantitative researchers develop techniques that can produce quantitative data (i.e., in the form of numbers). Thus, the researcher moves from abstract ideas to specific data collection techniques to precise numerical information produced by the techniques. The numerical information is an empirical representation of the abstract ideas. Data for qualitative researchers sometimes are in the form of numbers; more often they include written or spoken words, actions, sounds, symbols, physical objects, or visual images. The qualitative researcher does not convert all observation into a single medium, such as numbers. Instead she or he develops many flexible, ongoing processes of measurement that leave the data in various shapes, sizes, and forms.
•   The third distinction is how the two styles make such connections. Quantitative researchers contemplate and reflect on concepts before they gather any data. They construct measurement techniques that bridge concepts and data. Qualitative researchers also reflect on ideas before data collection, but they develop many, if not most, of their concepts during data collection. The qualitative researcher re-examines and reflects on the data and concepts simultaneously and interactively.