Observational study designs are used to assess potential causation in exposure-outcome relationships

Critical appraisal in observational studies

• Critical appraisal is important in observational designs as there is generally more conflict than in trials
• Ultimately used to inform guidelines e.g. SIGN
• Allows translation of research into 'real-life' clinical medicine
• STROBE: guideline for reporting observational studies (vs. CONSORT for RTCs)

Types of observational designs

Observational interventional designs ('natural experiments')

• Interrupted time series: method of statistical analysis involving tracking a long-term period before and after a point of intervention to assess the intervention's effects
• Non-randomised cohort: main design before and after, can be improved with addition of controls but always have unknown confounding variables so difficult to determine causality

Observational analytical designs

• Include cohort studies, case control studies, and cross sectional studies

Observational descriptive studies

• Case reports and case series - a report on a series of patients with an outcome of interest, no control group is used

Cohort design

• Cohort consists of a group/population followed overtime
• Enrolled at a baseline with comprehensive measurement and followed-up for a fixed length of time e.g. 10 years

Different types of cohort studies

Prospective

• Cohort followed forward in time from present