I'm reading a research paper.

It's about the effects of test offerings (opt in, opt out or active choice) to patients on the acceptance of the test. (%)

There's a section, which includes a sentence that I have no idea what it's talking about!

I'm very new to statistics and maths, so can someone please explain what it means in simple language!

"The effects of test offer scripts persisted when dummy variable fixed effect indicator variables for each study staff member who offered tests were included"

Thank you!