Points to consider Study design Study population Case definition Confounders Exposure definition and ascertainment Study size
Possible designs Cohort study in general population Cohort study of groups selected by exposure Case-control study based on hospital admissions Cross-sectional survey of occupations selected by exposure
Case definition and ascertainment Questionnaire about symptoms and past treatment Physician diagnosis based on physical examination Doppler studies Hospital diagnosis
Exposure definition and ascertainment Based on duration of standing without walking Based on duration of standing/walking Assessed by questionnaire By goniometry By observation By inference from job title