Diet and colorectal cancer in UK Biobank: a prospective study Background: UK Biobank is a prospective cohort study of half a million men and women aged 40-69years recruited from across the UK between 2006 and 2010. Potential participants were identified from National Health Service patient registers and invited to attend a local assessment center. At the assessment center, the participants completed a touchscreen questionnaire, which collected information on sociodemographic characteristics and diet, lifestyle, reproductive and environmental factors. Anthropometric measurements were taken using standardized procedures. The study excluded participants with prevalent cancer [other than nonmelanoma skin cancer, International Classification of Diseases - resulting in (219329 men and 256252 women)]. The number of participants in each analysis of food or nutrient and colorectal-cancer risk varies slightly, due to missing information for the exposure of interest [participants who selected 'do not know' or 'prefer not to answer for the question(s). Categorization: Participants are categorized according to their intake at recruitment. Mean intake in each category is from the web-based 24-hour dietary assessments. Trend per increment uses the re-measured intakes from the web-based 24-hour dietary assessments. Models were stratified by age (<45, 45-, 50-, 55-, 60-, 65years), sex, geographical region (10 regions) and socio-economic status (in fifths, based on the Townsend deprivation index14) and adjusted for education (College or University degree, vocational qualifications, optional national exams at ages 17-18years, national exams at age 16years, none of the above, unknown), smoking status (never, past, current <10 cigarettes per day, current 10-14 cigarettes per day, current 15-19 cigarettes per day, current 20+ cigarettes per day, unknown), waist circumference (sex-specific fifths, unknown), height (sexspecific fifths, unknown), physical activity [low: <10 excess metabolic equivalent (MET)-hours per week, moderate: 10-49.9 excess MET-hours per week, high: 50 excess MET-hours per week, unknown15], alcohol intake (<1, 1-7, 8-15, 16g/day, unknown) (except for analyses where alcohol was the main exposure), family history of colorectal cancer (mother, father or sibling having had colorectal cancer, no family history, unknown), aspirin or ibuprofen use (regular use, not regular use, unknown), use of vitamin D supplements (regular use, not regular use, unknown), use of folate supplements (regular use, not regular use, unknown) and in women only: parity (0, 1-2, 3 live births, unknown), menopause (pre-menopausal, post-menopausal, unsure because of hysterectomy, unsure because of other reason, unknown), oral contraceptive agent (OCA) use.

Questions: What is the researcher's sampling design for this study? What are the explanatory, response and potential confounding variables? Explain if and/or how probability sampling was incorporated and how there may be potential sampling bias. Discuss the sample size and whether you believe the sample size is appropriate. Analyze how the data used in the study are either sound and reliable or how the data are likely biased.