Having read the article from New Scientist I’m left with the question which isn’t answered… Isn’t there a possibility that the people who write diaries regularly probably going to be the character type who have the medical and phsychological problems described as the consiquences of diary writing in the article?
From what I can see, the only way to prove or disprove this would be to find a large sample of non-diary writers, do a medical on them all and then get half to start writing diaries without telling them what the study is for (so as not to cause a placebo effect). Just testing those who are already writing or not writing is pointless as you can’t separate cause and effect.
Sometimes I dispair about the psychologists (and many medical researchers) who seem to be pseudo-scientists who abuse statistics to prove the conjecture they formulated before the study. A true scientist should try as hard as they can to knock down their own conjecture or theory and only if it withstands every attack they can think of start to believe it might hold some sense of truth.