Why most published research findings are false

John PA Ioannidis · 2005
DOI: 10.1371/journal.pmed.0020124

Corollaries:

  1. The smaller the studies conducted in a scientific field, the less likely the research findings are to be true.
  2. The smaller the effect sizes in a scientific field, the less likely the research findings are to be true.
  3. The greater the number and the lesser the selection of tested relationships in a scientific field, the less likely the research findings are to be true.
  4. The greater the flexibility in designs, definitions, outcomes, and analytical modes in a scientific field, the less likely the research findings are to be true.
  5. The greater the financial and other interests and prejudices in a scientific field, the less likely the research findings are to be true.

How Can We Improve the Situation:

  1. Better powered evidence.
  2. The totality of the evidence (including all false discoveries).
  3. Instead of chasing statistical significance, we should improve our understanding of the pre-study odds.

Excerpts

Let us suppose that in a research field there are no true findings at all to be discovered. History of science teaches us that scientific endeavor has often in the past wasted effort in fields with absolutely no yield of true scientific information, at least based on our current understanding. In such a “null field,” one would ideally expect all observed effect sizes to vary by chance around the null in the absence of bias. The extent that observed findings deviate from what is expected by chance alone would be simply a pure measure of the prevailing bias.

Abstract

There is increasing concern that most current published research findings are false. The probability that a research claim is true may depend on study power and bias, the number of other studies on the same question, and, importantly, the ratio of true to no relationships among the relationships probed in each scientific field. In this framework, a research finding is less likely to be true when the studies conducted in a field are smaller; when effect sizes are smaller; when there is a greater number and lesser preselection of tested relationships; where there is greater flexibility in designs, definitions, outcomes, and analytical modes; when there is greater financial and other interest and prejudice; and when more teams are involved in a scientific field in chase of statistical significance. Simulations show that for most study designs and settings, it is more likely for a research claim to be false than true. Moreover, for many current scientific fields, claimed research findings may often be simply accurate measures of the prevailing bias. In this essay, I discuss the implications of these problems for the conduct and interpretation of research.

Reference

John PA Ioannidis “Why most published research findings are false” (2005) DOI: 10.1371/journal.pmed.0020124

@Article{ioannidis2005,
  title = {Why most published research findings are false},
  author = {Ioannidis, John PA},
  journal = {PLoS medicine},
  abstract = {There is increasing concern that most current published research findings are false. The probability that a research claim is true may depend on study power and bias, the number of other studies on the same question, and, importantly, the ratio of true to no relationships among the relationships probed in each scientific field. In this framework, a research finding is less likely to be true when the studies conducted in a field are smaller; when effect sizes are smaller; when there is a greater number and lesser preselection of tested relationships; where there is greater flexibility in designs, definitions, outcomes, and analytical modes; when there is greater financial and other interest and prejudice; and when more teams are involved in a scientific field in chase of statistical significance. Simulations show that for most study designs and settings, it is more likely for a research claim to be false than true. Moreover, for many current scientific fields, claimed research findings may often be simply accurate measures of the prevailing bias. In this essay, I discuss the implications of these problems for the conduct and interpretation of research.},
  doi = {10.1371/journal.pmed.0020124},
  volume = {2},
  number = {8},
  pages = {e124},
  year = {2005},
  publisher = {Public Library of Science}
}