Sandelowski, M. (2001). Real qualitative researchers do not count: The use of numbers in qualitative research. Research in Nursing & Health, 24(3), 230–240. https://dx.doi.org/10.1002/nur.1025

Sandelowski (2001) provides a very comprehensive review of the use of numbers, numeric expressions and mathematical calculations in recording and explaining lived experience and verbally expressed phenomena – illustrated by multiple examples from nursing and health.

Sandelowski, M., Voils, C. I., & Knafl, G. (2009). On quantitizing. Journal of Mixed Methods Research, 3(3), 208–222. https://doi.org/10.1177/1558689809334210

Sandelowski et al. (2009) review a wide range of issues and assumptions involved in converting qualitative data to generate counts for use in statistical analyses.