This function can be used to establish how many participants are required to establish a prevalence rate with a given margin of error.
prevalencePower(expectedPrevalence, marginOfError = 0.05, conf.level = 0.95)
expectedPrevalence | The expected prevalence. |
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marginOfError | The desired precision. |
conf.level | The confidence of the confidence interval. |
Note that when uncertain as to the expected prevalence, it's better to assume a prevalence closer to 50%. Prevalences closer to 0% or 100% are easier to detect and therefore have more power.
The required number of participants.
### Required participants for detecting a prevalence of 10% ### with a 95% confidence interval of 10% wide: prevalencePower(.1);#> [1] 138.2925### Required participants for detecting a prevalence of 10% ### with a 95% confidence interval of 4% wide: prevalencePower(.1, .02);#> [1] 864.3282### Required participants for detecting a prevalence of 60% ### with a 95% confidence interval of 10% wide: prevalencePower(.6);#> [1] 368.78