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# Resources

#### GLOSSARY

• Body mass index (BMI):
The value calculated by dividing an individual’s weight in kilograms by the square of the individual’s height in metres; used as an indicator of general body weight status.

• Cohort study:
A study that follows a group of individuals (a cohort) through time, collecting data such as information about sociodemographic characteristics (e.g. age, gender, education level, and profession), lifestyle characteristics (e.g. diet, tobacco use, and alcohol consumption), and biomedical characteristics (e.g. cholesterol level, history of diseases, and treatments), with the aim of finding associations between these characteristics and the occurrence of disease or death.

• Longitudinal analysis:
When a variable (such as BMI) is collected repeatedly through time within the same group of individuals, information about the trajectory of this variable through time may be useful; however, it can be difficult to estimate an individual’s trajectory on the basis of observed measurements alone, because there are often different numbers of measurements made at different time points from one participant to the next. Longitudinal analysis is based on statistical models that use the measurements from all individuals to create an average trajectory; individual-specific trajectories are then computed as deviations from this average trajectory, according to pre-defined distributional assumptions.

• Obesity-related cancers:
Cancers for which there is convincing scientific evidence of a causal link with obesity; these include oesophageal adenocarcinoma and cancers of the colon, rectum, kidney, pancreas, gallbladder, postmenopausal breast, corpus uteri, and ovary.

• Time-to-event analysis:
A type of statistical analysis used to study the effect of risk factors on the occurrence of a particular health outcome (e.g. disease, relapse, or death). The general purpose is to compare the times of occurrence among individuals with different levels of exposure to the risk factors. One of the most commonly used models for studying time-to-event data is the Cox proportional hazard regression model.

#### PUBLICATIONS

• Arnold M, Freisling H, Stolzenberg-Solomon R, Kee F, O’Doherty MG, Ordóñez-Mena JM, et al. (2016). Overweight duration in older adults and cancer risk: a study of cohorts in Europe and the United States. Eur J Epidemiol. 31(9):893–904. PMID: 27300353

• Arnold M, Jiang L, Stefanick ML, Johnson KC, Lane DS, LeBlanc ES, et al. (2016). Duration of adulthood overweight, obesity, and cancer risk in the Women’s Health Initiative: a longitudinal study from the United States. PLoS Med. 13(8):e1002081 PMID: 27529652