1 / 20

Case-Crossover Studies

Case-Crossover Studies. Analytic Study Designs. Case-crossover study: • Only subjects (cases) who have experienced the disease of interest are selected. • Investigator postulates a critical exposure period (“empirical induction period”) for the exposure of interest.

johnnysimon
Télécharger la présentation

Case-Crossover Studies

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Case-Crossover Studies

  2. Analytic Study Designs Case-crossover study: • Only subjects (cases) who have experienced the disease of interest are selected. • Investigator postulates a critical exposure period (“empirical induction period”) for the exposure of interest. • Presence of the exposure is compared between the critical exposure period and other periods of exposure (e.g. conditional odds ratio). • Good for studying effects of transient exposures.

  3. Analytic Study Designs Case-crossover study: (B) (A) Hypothesized irrelevant (non-causal) exposure Hypothesized relevant (causal) exposure Outcome event Normal background risk “Empirical induction period” Compare presence of exposure between hypothesized non-causal (A) and hypothesized causal (B) periods of exposure

  4. Analytic Study Designs Case-crossover study: • Biased selection of controls (selection bias) is eliminated (assuming matched analysis is conducted) since controls represent the population that produced the cases. • Since each subject serves as their own control, thus, “fixed” confounders are eliminated. • However, confounding can occur from factors that vary over time and are associated with the exposure and disease of interest (e.g. smoking).

  5. Analytic Study Designs Case-crossover study: • If exposure ascertainment differs between the case and control intervals, information bias may be present. • Overestimation or underestimation of the empirical induction period results in non- differential misclassification – hence bias towards the null.

  6. Case control vs. case-crossover From the topics listed below, select whether the case-control or case-crossover study design is more appropriate.

  7. Case control vs. case-crossover From the topics listed below, select whether the case-control or case-crossover study design is more appropriate.

  8. Review of Recommended ReadingTraffic law enforcement and risk of crashes --- Case-crossover study designed to assess effect of prior driving conviction on subsequent risk of fatal vehicle crashes. --- Identified all drivers involved in fatal crashes between 1988 and 1999 in Ontario, Canada. --- Matched date of fatal crash to previous driving history records (convictions) in Ontario in 1-month period before (case period) and 13-months before (control period) crash. --- Most common prior driving conviction was speeding, with crashes and convictions more common in the summer. --- Explored how long a potential association with prior driving convictions may have persisted.

  9. Discussion Question 1 Interpret the results in figure 1 and table 2, including use of alternate control periods and among various subgroups. Do these results support the primary study hypothesis? Source: Lancet 2003; 361:2177-2182.

  10. Discussion Question 2 Interpret the results in figure 2. Do the results suggest that the effect of traffic law enforcement on risk of crashes persists over time? Source: Lancet 2003; 361:2177-2182.

  11. Discussion Question 3 Which of the following potential sources of confounding were essentially eliminated by the use of the case-crossover design? ●Age ● # prior driving convictions ●Gender ● # years as licensed driver ●Alcohol use while ● cell phone use while driving Source: Lancet 2003; 361:2177-2182.

  12. Cross-Sectional Studies

  13. Cross-Sectional Study • Both a descriptive and analytic study design. • Snapshot of the health status of populations at a certain point in time. • For each subject, exposure and disease outcome are assessed simultaneously (hence also called a “prevalence study/survey”). • Compare prevalence of disease in persons with and without the exposure of interest (e.g. prevalence ratio – same formula as risk ratio).

  14. Cross-Sectional Study Advantages: • Quick, easy, and cheap. • Can study multiple exposures and disease outcomes simultaneously. • Good for describing the magnitude and distribution of health problems.

  15. Cross-Sectional Study Disadvantages: • Prevalent rather than incident cases of disease are identified – exposures may be associated with survival rather than risk of development of disease. • “Chicken or egg” dilemma – do not know whether the exposure preceded disease, or was a consequence of disease development.

  16. Cross-Sectional Study Example: Hypothesis: Obesity is a risk factor for knee osteoarthritis Sample: 100 retirees living at “University Village”

  17. Cross-Sectional Study Medical exam + X-rays to diagnose osteoarthritis of the knee Osteoarthritis - + 50 + 40 10 Obesity - 50 20 30

  18. Cross-Sectional Study Prevalence of osteoarthritis among obese subjects: 40/50 = 0.8 Prevalence of osteoarthritis among non-obese subjects: 20/50 = 0.4 Prevalence ratio = 0.8/0.4 = 2.0

  19. Cross-Sectional Study Obese subjects are two times more likely to have osteoarthritis of the knee than non-obese subjects.

  20. Cross-Sectional Study Chicken or egg dilemma What came first? Obesity or Osteoarthritis

More Related