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Figure 1 | BMC Cardiovascular Disorders

Figure 1

From: Risk of valvular heart disease associated with use of fenfluramine

Figure 1

Effect of adding cases from competing causes on the odds ratio in a case control study. In this hypothetical example of 500 exposed and 500 unexposed persons, when no extra cases were added (far left) there were 18 cases of disease in the exposed and 2 cases among the unexposed yielding an odds ratio of 9.30 (p value = 0.0007). Adding an equal number of cases due to unrelated causes to both the exposed and unexposed groups results in dilution of the odds ratio. The odds ratio drops below 2 after 16 cases are added and becomes non-significant after 21 cases are added (representing just 4.2% of exposed or unexposed groups).

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