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Bios 101 Lecture 2

Bios 101 Lecture 2. September 27, 2011. Hierarchy of Designs. Meta-Meta analysis. Experimental. Systematic reviews of RCTS. Analytic . Well conducted RCTs. Descriptive. Observational studies: Cross-sectional, Case-control, Cohort, Hybrid. Time series.

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Bios 101 Lecture 2

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  1. Bios 101 Lecture 2 September 27, 2011

  2. Hierarchy of Designs Meta-Meta analysis Experimental Systematic reviews of RCTS Analytic Well conducted RCTs Descriptive Observational studies: Cross-sectional, Case-control, Cohort, Hybrid Time series Ecological studies/Correlational studies Case series and case reports Expert opinion, usual practice

  3. Overview • Designs of epidemiological studies tries to explain disease occurrence patterns and are used to determine whether an association exists between an exposure and disease • Involves exposures, outcomes and confounders • Many ways to evaluate the association between exposure and an outcome

  4. Descriptive Designs: Individual level • Case Report: Describe the experience of a single patient • Case series: Describe the experience of group of patients with similar diagnosis • observe certain clinical features of a disease, its symptoms, tratment and outcomes • Studying symptoms and signs • Creating case definitions • Clinical education, audit and research Unnikrishnan AG, Rajaratnam S, John GT, Stephen C. Boy with 'rainbow' urine. NephrolDial Transplant. 2001 Oct;16(10):2097-9. Vermeiren P, Vantilborgh A, Offner F. Myeloma of the central nervous system: report of a single center case series. ActaClin Belg. 2011 May-Jun;66(3):205-8.

  5. Descriptive Designs: Population level • Ecological Studies: used to determine whether association exists in groups or populations or over time relating to population characteristics thought to be at risk . • Most ecological analyses are based on population case-series. • Ecological analyses are subject to the ecological fallacy.

  6. Time-series studies • Also called Before–after studies (indiviuals) • Examine cumulative incidence rates over time

  7. Analytical Studies has comparison group Grimes et al. Lancet 2002;359:57-61

  8. Cross-sectional Studies/ Prevalence studies • Characteristics: detects point prevalence; relative conditions • Merits: feasible; quick; economic; allows study of several diseases / exposures; useful for estimation of the population burden, health planning and priority setting of health problems • Limitations: temporal ambiguity; not suitable for rare conditions; liable to survivor bias Szklo & Nieto. Epidemiology: beyond the basics. Aspen Publishers, 2000

  9. Cross-sectional study

  10. Case-control study Characteristics: two source populations; assumption that non-cases are representative of the source population of cases. Merits: efficient in terms of time, money and effort; suitable for rare diseases; suitable for investigating diseases with long latency period (eg. Cancer) Limitations: not suitable for rare exposures; liable to selection bias and recall bias Szklo & Nieto. Epidemiology: beyond the basics. Aspen Publishers, 2000

  11. Case-control study Grimes et al. Lancet 2002;359:431-34

  12. Cohort Study Characteristics: follow-up period (prospective; retrospective) Merits: no temporal ambiguity; multiple outcomes could be studied at the same time from same exposure; suitable for incidence estimation, rare exposures, reduce risk of survivor bias Limitations (of prospective type): expensive; time-consuming; inefficient for rare diseases; selection bias, loss to follow-up in many studies Szklo & Nieto. Epidemiology: beyond the basics. Aspen Publishers, 2000

  13. Cohort Study

  14. Variations in Cohort Study designs Eg: Concurrent study: Cigarette smoking and Lung cancer Hammond and Horn, JAMA, 1958, 166: 1159-1308 Eg: Nonconcurrent study: Exposure to P32 and/or Xray increases leukemia in patients with Polycytheimavera. Modan and Lilienfeld, Medicine, 1965, 44: 305-344 Grimes et al. Lancet 2002;359:341-45

  15. Hybrid Studies • Nested Case control Study • Case control study within a cohort study • Normally 4 to 5 controls per case • Case cross-over study • Variant of case-control study • Used for settings where risk of outcome is increased for a short time following exposure • Cases serve as their own controls • Case Cohort Study • whole cohort is subject to case-identification, but only a random sample (called the sub-cohort) receives detailed exposure assessment. • The cases are those emerging in the population (both in and out of the sub-cohort); the controls are subjects in the sub-cohort who are notcases.

  16. Experimental Designs • Will continue in next class

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