I’m not exactly sure what you mean by a formal job change, but a change in occupation codes could signify several different possibilities. The individual could have had a change in occupation due to switching jobs between firms, changed their job within the firm, or have had the main duties of their job within the firm altered. Moreover, if the occupation code is the same, this does not mean that the respondent was continuously employed. They could have transferred from one firm to another, but have kept the same occupation across firms.
Instead of using the ASEC longitudinal samples with OCC, you might find using EMPSAME together with the Basic Monthly Surveys more conducive to answering your research question. EMPSAME reports whether the respondent was employed by the same employer and had the same job as their main job in the previous month’s survey. Since the CPS is a rotating panel, you will be able to link individuals and their responses to EMPSAME across months within a 16-month period (more on the rotating panel here). If you decide to use EMPSAME, please note the issue of not-in-universe observations described on the variable page.
Additionally, you might also be interested in looking at the Job Tenure & Occupational Mobility Supplement (asked in January in every even year). JTYEARS, available in this supplement, reports the number of years the respondent worked in their current job. More specifically, it asks for “how long the respondent has been working continuously for their current company or as a self-employed person at their main job for their present employer”. If you do plan to use this supplement, please review the notes IPUMS CPS provides for it.
