Evid Based Nurs 15:34 doi:10.1136/ebnurs-2012-100524
  • Research made simple

What is a p value and what does it mean?

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  1. Dorothy Anne Forbes
  1. Correspondence to Dorothy Anne Forbes
    Faculty of Nursing, University of Alberta, Level 3, Edmonton Clinic Health Academy, Edmonton, Alberta, T6G 1C9, Canada; dorothy.forbes{at}

Researchers aim to make the strongest possible conclusions from limited amounts of data. To do this, they need to overcome two problems. First, important differences in the findings can be obscured by natural variability and experimental imprecision. Thus, it is difficult to distinguish real differences from random variability. Second, researchers' natural inclination is to conclude that differences are real, and to minimise the contribution of random variability. Statistical probability minimises this from happening.1

Statistical probability or p values reveal whether the findings in a research study are statistically significant, meaning that the findings are unlikely to have occurred by chance. To understand the p value …

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