### Abstract

Background: Sample sizes set on the basis of desired power and expected effect size are often too small to yield a confidence interval narrow enough to provide a precise estimate of a population value. APPROACH: Formulae are presented to achieve a confidence interval of desired width for four common statistical tests: finding the population value of a correlation coefficient (Pearson r), the mean difference between two populations (independent- and dependent-samples t tests), and the difference between proportions for two populations (chi-square for contingency tables). Discussion: Use of the formulae is discussed in the context of the two goals of research: (a) determining whether an effect exists and (b) determining how large the effect is. In addition, calculating the sample size needed to find a confidence interval that captures the smallest benefit of clinical importance is addressed.

Original language | English (US) |
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Pages (from-to) | 148-153 |

Number of pages | 6 |

Journal | Nursing Research |

Volume | 60 |

Issue number | 2 |

DOIs | |

Publication status | Published - Mar 1 2011 |

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### Cite this

*Nursing Research*,

*60*(2), 148-153. https://doi.org/10.1097/NNR.0b013e318209785a