How do I reference the Prochaska and DiClemente (1983) stages of change model in APA (7th ed.)?
Wherever possible you should use the original work.
Prochaska, J. O., & DiClemente, C. C. (1983). Stages and processes of self-change of smoking: Toward an integrative model of change. Journal of Consulting and Clinical Psychology, 51(3), 390-395. http://dx.doi.org/10.1037/0022-006X.51.3.390
If you have not read the original you must make this clear by referring to the work in which you found the reference. In the reference list only include details of the work that you read.
Prochaska and DiClemente (1983) as cited in Prestwich et al. (2018) shows that…
...(Prochaska & DiClemente, 1983, as cited in Prestwich et al., 2018).
In the reference list
Prestwich, A., Kenworthy, J., & Conner, M. (2018). Health behavior change : Theories, methods and interventions. Routledge.