To evaluate the calibration of a disease risk prediction tool, the quantity E/O, i.e. the ratio of the expected to the observed number of events, is usually computed. However, because of censoring, or more precisely because of individuals who drop out before the termination of the study, this quantity is generally unavailable for the complete population study and an alternative estimate has to be computed. In this paper, we present and compare four methods to do this. We show that two of the most commonly used methods generally lead to biased estimates. Our arguments are first based on some theoretic considerations. Then, we perform a simulation study to highlight the magnitude of biases. As a concluding example, we evaluate the calibration of an existing predictive model for breast cancer on the E3N-EPIC cohort.

Objectives: To evaluate the performance of a short dietary questionnaire, using weights to estimate nutrient intake. Design: Using dietary data collected in 1993-1995 from a large cohort of French women, stepwise regression analysis was used to identify the food groups that best predicted nutrient intakes, resulting in a short list of twenty-three foods. This list was used to design a twenty-three-item dietary questionnaire. Nutrient intake was estimated from the answers to the twenty-three questions, applying weights to each response. Weights were calculated from the large database as regression coefficients of the nutrient intake against the twenty-three food groups. In [2005][2006] 103 women responded (at a 1-year interval) to both the short questionnaire and a previously validated dietary history questionnaire. Intakes of twenty nutrients and energy estimated from these two questionnaires were compared. Setting: French adult female population. Subjects: For developing the instrument, 73 034 women aged 41-72 years; for testing, 103 women aged 55-80 years in 2005. Results: Mean nutrient intakes generally differed by less than 10 % between the two methods. Correlation coefficients of nutrient intakes ranged from 0?23 for vitamin D to .0?65 for Mg, vitamin B 3 and alcohol. For most nutrients, at least 70 % of subjects fell into the same or an adjacent quintile when classified by either of the two questionnaires. Conclusions: In light of both its strengths and limitations, this short questionnaire could be used in French adult women to obtain some general nutritional information, notably for adjustment purposes when response to an extensive questionnaire cannot be obtained. Keywords Nutrient Dietary questionnaire Evaluation study Epidemiological method PreventionCurrently, the leading causes of death in developed countries are chronic diseases such as cancer, CVD and dementia. Diet appears to play a major role in their aetiology (1)(2)(3) . Therefore, reliable assessment of nutritional intake is needed for epidemiological studies but also for screening of potentially inappropriate diets. Several tools are available, including 24 h recall and FFQ, but they require time for completion and are often difficult to interpret. Other instruments are simpler, but were designed to assess intake only of specific nutrients (4)(5)(6)(7) . We sought to estimate a wide range of nutritional intakes and thus developed an original dietary assessment method based on responses to a twenty-three-item dietary questionnaire. We performed an evaluation study of this method in a sample of 103 French women. We report here its capacity to estimate twenty nutrient and energy intakes, taking as the reference a previously validated dietary history questionnaire. Methods Development of the instrumentSelection of food items that predict nutrient intake In developing the short questionnaire, we concentrated our efforts on dietary intake assessment of five nutrients often known to be in deficit in the French female population: Ca, Fe, M...

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