The diaries used in this study were designed to be easy to use and to be suitable for a diverse sample of the population. We first compared them with 24 hour audiotape recordings of the infants' vocalisations. Crying refers to a complex act that includes elements of movement, facial expression, and voice, and is usually interpreted as expressing a negative emotion. In the tape recordings the vocal part of crying is designated as negative vocalisation compared with neutral sounds (such as grunting) and positive sounds (such as cooing).Secondly, the sociodemographic characteristics of parents who returned diaries with readable data were compared with those of parents who did not from a population sample in a prospective cohort study. Thus the findings describe quantitative associations between negative vocalisations and the diary records of crying and fussing, they illustrate the limitations of both techniques in assessing the amount of infant crying, and they indicate the potential limits on the use of diaries for this purpose in the general population. Subjects and methodsTen mothers (who spoke fluent English or French) of normal 6 week old infants, who were in the nursery of a large general hospital associated with the university or a community health unit volunteered to take part in the comparison of diaries and tape recordings. The mean age of the infants was 6-3 weeks (range 5-5-7) at the time of recording; there were five boys and five girls, and seven were exclusively breast fed. The mean (SD) socioeconomic score measured by Green's two factor index8 was 67-8 (11.7), a wide range that is typical of this community.9 Informed consent was obtained before the tape recordings were made.

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