Q J Med 2002; 95: 247-249
© 2002 Association of Physicians
The nature of truth: Simpson's Paradox and the limits of statistical data
M. Heydtmann
From the Liver Research Laboratories, Queen Elizabeth Hospital, Birmingham, UK
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Introduction
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‘Give me a fruitful error any time, full of seeds, bursting
with its own corrections. You can keep your sterile truth for
yourself.’ Vilfredo Pareto
We usually think in terms of true and false, and often believe that we know which is which. Nonetheless, sometimes information which appears to be true is in fact false. Although we try to base our medical knowledge on objective evidence—research and statistics—rather than our personal opinions, Simpson's Paradox reminds us of the limitations of statistical evidence. In this phenomenon, an apparent paradox arises because aggregated data can support a conclusion which is opposite from that suggested by the same data before aggregation.
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An example
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One would generally conclude from the data in Table 1
that treatment
A is the treatment of choice for the condition studied (given
that side-effects are equal). Suppose, however, that these patients
consisted of two subgroups: those with a high serum level
. . . [Full Text of this Article]
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Is Simpson's Paradox dependent on the absolute numbers, and does statistical significance protect from the effect?
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Does a properly designed trial prevent Simpson's Paradox?
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Is Simpson's Paradox common?
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Acknowledgments
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Notes
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References
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