To me it seems very necessary to state whether they are talking about all people or all females when comparing groups who did or did not have painful periods.
Academics at the University of Oxford analysed data from more than 1,100 participants in the Avon Longitudinal Study of Parents and Children and found that, compared with those who did not have painful menses, those with severe period pain (dysmenorrhoea) at 15 years old had a 76% higher risk of chronic pain by the age of 26, while those with moderate period pain were 65% more likely to have chronic pain as adults.
'Higher risk' or 'more likely' than other females or all people of the same age? After all, I imagine that sex and perception/experience of pain are not unrelated.