Thanks for linking the graph, that's kind of wild. I agree with you that the lowest datapoint seems crazy. I can think of a few explanations.
- Random bad luck.
- As you say, failing to control for something -- although, if you then treat the lowest datapoint as being effectively the default risk, this would suggest support for radiation hormesis (that people who got a bit more than background radiation actually did better.)
- Some kind of data collection artifact. Perhaps the people with the absolute lowest dose, in a radiation-worker dataset, are selected for being ones who are not getting an accurate measurement (i.e. sloppy about wearing dose badges or something), and those people genuinely do have worse outcomes.
- Random bad luck.
- As you say, failing to control for something -- although, if you then treat the lowest datapoint as being effectively the default risk, this would suggest support for radiation hormesis (that people who got a bit more than background radiation actually did better.)
- Some kind of data collection artifact. Perhaps the people with the absolute lowest dose, in a radiation-worker dataset, are selected for being ones who are not getting an accurate measurement (i.e. sloppy about wearing dose badges or something), and those people genuinely do have worse outcomes.