Confidence intervals of effect size in randomized comparative parallel-group studies

Stat Med. 2006 Feb 28;25(4):639-51. doi: 10.1002/sim.2346.


We have presented a new likelihood-based approach for constructing confidence intervals of effect size that are applicable to small samples. We also conduct a simulation study to compare the coverage probability of the new likelihood-based method with other three methods proposed by Hedges and Olkin and Kraemer and Paik. Simulation studies show that the confidence interval generated by the modified signed log-likelihood ratio method possesses essentially exact coverage probabilities even for small samples, although the coverage probabilities are consistently but slightly less than the nominal level. The methods are also applied to two examples.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anthelmintics / pharmacology
  • Anthelmintics / therapeutic use
  • Blood Pressure / physiology
  • Computer Simulation
  • Confidence Intervals*
  • Humans
  • Hypertension / pathology
  • Likelihood Functions*
  • Randomized Controlled Trials as Topic / methods*
  • Sheep
  • Sheep Diseases / parasitology


  • Anthelmintics