Don’t confuse “associated with survival” with “the cause of survival”

Researchers studying adults in their 70s through 110s found that people over 100 had unusually high proportions of a rare type of immune cell, CD4 cytotoxic T lymphocytes, which can kill abnormal or cancerous cells.

The tempting headline is:

“Scientists discovered why people live to 100.”

They didn’t.

They discovered a biological difference associated with extreme longevity.

Those immune cells might help people survive longer.

Or people who survive longer may develop those cells.

Or a third factor could cause both.

This is one of the most useful habits in statistical thinking:

Association tells you where to investigate; causation tells you what to change.

Medicine, nutrition and exercise headlines constantly blur that distinction.

Thinking Lens

When a study says “people who do/have X live longer,” ask:

Did X create the outcome—or did the kind of person who reaches the outcome also tend to have X?

That question prevents a fascinating observation from becoming premature advice.