Diary studies, otherwise known as User Research Diaries or “Cultural probes” were pioneered for use in design research by William “Bill” Gaver, Professor at Goldsmiths London. Interestingly he doesn’t analyse diary content, nor does he create scenarios or personas from them instead using them as a base from which to validate other data. He does not create personas, preferring instead to revisit the raw data.
Diary studies are used in longitudinal research — looking at people over a longer period of time than a typical Contextual Inquiry or interview can allow; and researching people when you could not otherwise be there with them.