In the Covid-19 survey the question about labour market activity was not asked in each wave, only whether the respondent was working or not. The full information about employment status is available only for the baseline (there are blwork and blnonwork questions).
So, to determine if one has become unemployed since the last interview one would need to:
a) for the first wave in which a given respondent participated, compare sempderived with blwork - if someone was employed at the baseline and in wave 1 sempderived=4, then we could assume they became unemployed (somewhat simplifying, as e.g. they could have retired),
b) for subsequent waves in which the respondent participated, compare sempderived in the current wave with the sempderived in the previous wave - previously employed, currently sempderived=4, thus unemployed (again, simplifying)
Of course, you would also need to include people who were unemployed at the baseline and did not work in the waves you are interested in.
If you wanted a more refined definition of unemployment then to identify unemployed, you could check whether they were not working AND searching for a job using julk4wk included a Job Search module in waves 3, 5, 7, 9.
Best wishes,
Understanding Society User Support Team
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