When can we conclude that treatments or programs "don't work'?

David Weisburd*, Cynthia M. Lum, Sue Ming Yang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


In this article, the authors examine common practices of reporting statistically nonsignificant findings in criminal justice evaluation studies. They find that criminal justice evaluators often make formal errors in the reporting of statistically nonsignificant results. Instead of simply concluding that the results were not statistically significant, or that there is not enough evidence to support an effect of treatment, they often mistakenly accept the null hypothesis and state that the intervention had no impact or did not work. The authors propose that researchers define a second null hypothesis that sets a minimal threshold for program effectiveness. In an illustration of this approach, they find that more than half of the studies that had no statistically significant finding for a traditional, no difference null hypothesis evidenced a statistically significant result in the case of a minimal worthwhile treatment effect null hypothesis.

Original languageAmerican English
Pages (from-to)31-48
Number of pages18
JournalAnnals of the American Academy of Political and Social Science
StatePublished - May 2003


  • Effect sizes
  • Null hypothesis significance testing
  • Statistical power
  • Statistical significance
  • What works


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