The performance of doctors embraces attitudes to practice, knowledge, and skills. It is the outward and visible expression of our professionalism. In general, people think highly of the medical profession in Britain; rising expectations are a mark of our success. Nevertheless, self regulation, on which our professional independence and self respect depend, cannot be taken for granted. Sympathetic critics such as lay people, sociologists, and doctors reflect a wider public perception that we seem reluctant to assure doctors' competence and protect patients from poor practice. There are also criticisms that we are not addressing the widespread dissatisfaction with the attitude of some doctors, including their paternalism and poor communication with both patients and colleagues, and are failing to make self regulation demonstrably effective and responsive.

In prospective studies of diet it is often necessary to know for how many days subjects should record food consumption in order to be able to rank subjects correctly according to their nutrient intakes. Data from six studies--of toddlers, families, schoolchildren, dietitians, pregnant women, and elderly subjects--were analyzed to estimate the number of recording days necessary for energy, 28 nutrients, and the ratio of polyunsaturated to saturated fatty acids (P:S). The most striking finding is that 7 d of diet record do not rank subjects with the degree of accuracy commonly assumed. For some nutrients, such as iron, zinc, nicotinic acid, and pyridoxine, it may be desirable to record diet over a number of short, separate periods to achieve the number of days required. For others, such as copper, retinol, carotene, vitamin B-12, polyunsaturated fatty acids, P:S, and alcohol, alternative methods of assessment based on dietary histories or questionnaires may be more appropriate.

Fifty-one male and female volunteers aged 18-90 years from a wide variety of social and occupational backgrounds completed 7284 assessments of portion size in relation to food photographs. Subjects were shown six portion sizes (two small, two medium and two large) for each of six foods, and asked to compare the amount on the plate in front of them to (a) a series of eight photographs showing weights of portions from the 5th to the 95th centile of portion size (British Adult Dietary Survey), or (b) a single photograph of the average (median) portion size. Photographs were prepared either in colour or in black and white, and in two different sizes. The order of presentation of foods; use of black and white or colour; the size of photographs; and presentation of eight or average photographs were each randomized independently. On average, the mean differences between the portion size presented and the estimate of portion size using the photographs varied from -8 to + 6 g (-4 to + 5 %) for the series of eight photographs, and from -34 to -1 g (-23 to +9%) for the single average photograph. Large portion sizes tended to be underestimated more than medium or small portion sizes, especially when using the average photograph (from -79 to -14 g, -37 to -13 %). Being female, 65 years and over, or retired, or seeing photographs in colour, were all associated with small but statistically significant overestimations of portion size. Having a body mass index 2 30 kg/m2 was associated with an 8% underestimate of portion size. We conclude that use of a series of eight photographs is associated with relatively small errors in portion size perception, whereas use of an average photograph is consistently associated with substantial underestimation across a variety of foods. Food photography: Dietary survey: EpidemiologyPhotographs of food have often been used in dietary surveys to help subjects estimate portion size. Typically, photographs are taken of small, medium and large portions which are judged to be representative of the range of portion sizes actually consumed. Subjects are then asked to identify which photograph best reflects either their usual portion size (e.g. in a diet history) or actual portion size (e.g. in a 24 h recall). Alternatively, a single photograph of average portion size is displayed, and subjects are asked to estimate their own portion size as a fraction, multiple or percentage of the amount shown in the photograph.A complex process takes place when a photograph is used to identify portion size during an interview or questionnaire completion. This process has three main elements : perception, conceptualization, and memory. Perception involves a subject's ability to relate an amount of food which is present in reality to an amount depicted in a photograph. Conceptualization concerns a subject's ability to make a mental construct of an amount of food which is not present in reality, and to relate that to a photograph. Memory will affect the precision of the conceptualization.

The aim of the present study was to determine the errors in the conceptualization of portion size using photographs. Male and female volunteers aged 18-90 years (n 136) from a wide variety of social and occupational backgrounds completed 602 assessments of portion size in relation to food photographs. Subjects served themselves between four and six foods at one meal (breakfast, lunch or dinner). Portion sizes were weighed by the investigators at the time of serving, and any waste was weighed at the end of the meal. Within 5 min of the end of the meal, subjects were shown photographs depicting each of the foods just consumed. For each food there were eight photographs showing portion sizes in equal increments from the 5th to the 95th centile of the distribution of portion weights observed in The Dietary and Nutritional Survey of British Adults (Gregory ef al. 1990). Subjects were asked to indicate on a visual analogue scale the size of the portion consumed in relation to the eight photographs. The nutrient contents of meals were estimated from food composition tables. There were large variations in the estimation of portion sizes from photographs. Butter and margarine portion sizes tended to be substantially overestimated. In general, small portion sizes tended to be overestimated, and large portion sizes underestimated. Older subjects overestimated portion size more often than younger subjects. Excluding butter and margarine, the nutrient content of meals based on estimated portion sizes was on average within 7 YO of the nutrient content based on the amounts consumed, except for vitamin C (21 YO overestimate), and for subjects over 65 years (15-20% overestimate for energy and fat). In subjects whose BMI was less than 25 kg/m2, the energy and fat contents of meals calculated from food composition tables and based on estimated portion size (excluding butter and margarine) were 540% greater than the nutrient content calculated using actual portion size, but for those with BMI 30 kg/m2 or over, the calculated energy and fat contents were underestimated by 2 5 % . The correlation of the nutrient content of meals based on actual or estimated portion sizes ranged from 0.84 to 0.96. For energy and eight nutrients, between 69 and 89 YO subjects were correctly classified into thirds of the distribution of intake using estimated portion size compared with intakes based on actual portion sizes. When 'average' portion sizes (the average weight of each of the foods which the subjects had served themselves) were used in place of the estimates based on photographs, the number of subjects correctly classified fell to between 60 and 79%. We report for the first time the error associated with conceptualization and the nutrient content of meals when using photographs to estimate food portion size. We conclude that photographs depicting a range of portion sizes are a useful aid to the estimation of portion size.Misclassification of subjects according to their nutrient intake from one meal is reduced when photographs are used to esti...