Description Usage Arguments Details Value Author(s) References See Also Examples

Sample size calculations for epidemiological studies

1 2 3 4 5 6 7 8 9 10 11 12 13 14 | ```
n.for.survey (p, delta = "auto", popsize = NULL, deff = 1, alpha = 0.05)
n.for.2means (mu1, mu2, sd1, sd2, ratio = 1, alpha = 0.05, power = 0.8)
n.for.cluster.2means (mu1, mu2, sd1, sd2, alpha = 0.05, power = 0.8, ratio = 1,
mean.cluster.size = 10, previous.mean.cluster.size = NULL,
previous.sd.cluster.size = NULL, max.cluster.size = NULL, min.cluster.size =
NULL, icc = 0.1)
n.for.2p (p1, p2, alpha = 0.05, power = 0.8, ratio = 1)
n.for.cluster.2p (p1, p2, alpha = 0.05, power = 0.8, ratio = 1,
mean.cluster.size = 10, previous.mean.cluster.size = NULL,
previous.sd.cluster.size = NULL, max.cluster.size = NULL,
min.cluster.size = NULL, icc = 0.1)
n.for.equi.2p(p, sig.diff, alpha=.05, power=.8)
n.for.noninferior.2p (p, sig.inferior, alpha = 0.05, power = 0.8)
n.for.lqas (p0, q = 0, N = 10000, alpha = 0.05, exact = FALSE)
``` |

`p` |
estimated probability |

`delta` |
difference between the estimated prevalence and one side of the 95 percent confidence limit (precision) |

`popsize` |
size of the finite population |

`deff` |
design effect for cluster sampling |

`alpha` |
significance level |

`mu1, mu2` |
estimated means of the two populations |

`sd1, sd2` |
estimated standard deviations of the two populations |

`ratio` |
n2/n1 |

`mean.cluster.size` |
mean of the cluster size planned in the current study |

`previous.mean.cluster.size, previous.sd.cluster.size` |
mean and sd of cluster size from a previous study |

`max.cluster.size, min.cluster.size` |
maximum and minimum of cluster size in the current study |

`icc` |
intraclass correlation coefficient |

`p1, p2` |
estimated probabilities of the two populations |

`power` |
power of the study |

`sig.diff` |
level of difference consider as being clinically significant |

`sig.inferior` |
level of reduction of effectiveness as being clinically significant |

`p0` |
critical proportion beyond which the lot will be rejected |

`q` |
critical number of faulty pieces found in the sample, beyond which the lot will be rejected |

`N` |
lot size |

`exact` |
whether the exact probability is to be computed |

'n.for.survey' is used to compute the sample size required to conduct a survey.

When 'delta="auto"', delta will change according to the value of p. If 0.3 <= p <= 0.7, delta = 0.1. If 0.1 <= p < .3, or 0.7< p <=0.9, then delta=.05. Finally, if p < 0.1, then delta = p/2. If 0.9 < p, then delta = (1-p)/2.

When cluster sampling is employed, the design effect (deff) has to be taken into account.

'n.for.2means' is used to compute the sample size needed for testing the hypothesis that the difference of two population means is zero.

'n.for.cluster.2means' and 'n.for.cluster.2p' are for cluster (usually randomized) controlled trial.

'n.for.2p' is used to the compute the sample size needed for testing the hypothesis that the difference of two population proportions is zero.

'n.for.equi.2p' is used for equivalent trial with equal probability of success or fail being p for both groups. 'sig.diff' is a difference in probability considered as being clinically significant. If both sides of limits of 95 percent CI of the difference are within +sig.diff or -sig.diff, there would be neither evidence of inferiority nor of superiority of any arm.

'n.for.noninferior.2p' is similar to 'n.for.equi.2p' except if the lower limit of 95 percent CI of the difference is higher than the sig.inferior level, the hypothesis of inferiority would be rejected.

For a case control study, p1 and p2 are the proportions of exposure among cases and controls.

For a cohort study, p1 and p2 are proportions of positive outcome among the exposed and non-exposed groups.

'ratio' in a case control study is controls:case. In cohort and cross-sectional studies, it is non-exposed:exposed.

LQAS stands for Lot Quality Assurance Sampling. The sample size n is determined to test whether the lot of a product has a defective proportion exceeding a critical proportion, p0. Out of the sample tested, if the number of defective specimens is greater than q, the lot is considered not acceptable. This concept can be applied to quality assurance processes in health care.

When any parameter is a vector of length > 5, a table of sample size by the varying values of parameters is displayed.

a list.

'n.for.survey' returns an object of class "n.for.survey"

'n.for.2p' returns an object of class "n.for.2p"

'n.for.2means' returns an object of class "n.for.2means"

'n.for.lqas' returns an object of class "n.for.lqas"

Each type of returned values consists of vectors of various parameters in the formula and the required sample size(s).

Virasakdi Chongsuvivatwong <[email protected]>

Eldridge SM, Ashby D, Kerry S. 2006
Sample size for cluster randomized trials:
effect of coefficient of variation of cluster size and analysis method.
*Int J Epidemiol* **35(5)**: 1292-300.

'power.for.2means', 'power.for.2p'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | ```
# In a standard survey to determine the coverage of immunization needed using
# a cluster sampling technique on a population of approximately 500000, and
# an estimated prevalence of 70 percent, design effect is assumed to be 2.
n.for.survey( p = .8, delta = .1, popsize = 500000, deff =2) # 123 needed
# To see the effect of prevalence on delta and sample size
n.for.survey( p = c(.5, .6, .7, .8, .9, .95, .99))
# Testing the efficacy of measles vaccine in a case control study .
# The coverage in the non-diseased population is estimated at 80 percent.
# That in the diseased is 60 percent.
n.for.2p(p1=.8, p2=.6) # n1=n2=91 needed
# A randomized controlled trial testing cure rate of a disease of
# 90 percent by new drugs and 80 percent by the old one.
n.for.2p(p1=.9, p2=.8) # 219 subjects needed in each arm.
# To see the effect of p1 on sample size
n.for.2p(p1=seq(1,9,.5)/10, p2=.5) # A table output
# The same randomized trial to check whether the new treatment is 5 percent
# different from the standard treatment assuming both arms has a common
# cure rate of 85 percent would be
n.for.equi.2p(p=.85, sig.diff=0.05) # 801 each.
# If inferior arm is not allow to be lower than -0.05 (5 percent less effective)
n.for.noninferior.2p(p=.85, sig.inferior=0.05) # 631 each.
# A cluster randomized controlled trial to test whether training of village
# volunteers would result in reduction of prevalence of a disease from 50 percent
# in control villages to 30 percent in the study village with a cluster size
# varies from 250 to 500 eligible subjects per village (mean of 350) and the
# intraclass correlation is assumed to be 0.15
n.for.cluster.2p(p1=.5, p2=.3, mean.cluster.size = 350, max.cluster.size = 500,
min.cluster.size = 250, icc = 0.15)
# A quality assurance to check whether the coding of ICD-10 is faulty
# by no more than 2 percent.The minimum sample is required.
# Thus any faulty coding in the sample is not acceptable.
n.for.lqas(p0 = .02, q=0, exact = TRUE) # 148 non-faulty checks is required
# to support the assurance process.
n.for.lqas(p0 = (1:10)/100, q=0, exact = FALSE)
``` |

```
Loading required package: foreign
Loading required package: survival
Loading required package: MASS
Loading required package: nnet
Sample size for survey.
Assumptions:
Proportion = 0.8
Confidence limit = 95 %
Delta = 0.1 from the estimate.
Population size = 5e+05
Design effect = 2
Sample size = 123
Sample size for survey.
Assumptions:
Confidence limit = 95 %
p delta n
1 0.50 0.100 96
2 0.60 0.100 92
3 0.70 0.100 81
4 0.80 0.050 246
5 0.90 0.050 138
6 0.95 0.025 292
7 0.99 0.005 1521
Estimation of sample size for testing Ho: p1==p2
Assumptions:
alpha = 0.05
power = 0.8
p1 = 0.8
p2 = 0.6
n2/n1 = 1
Estimated required sample size:
n1 = 91
n2 = 91
n1 + n2 = 182
Estimation of sample size for testing Ho: p1==p2
Assumptions:
alpha = 0.05
power = 0.8
p1 = 0.9
p2 = 0.8
n2/n1 = 1
Estimated required sample size:
n1 = 219
n2 = 219
n1 + n2 = 438
Assumptions:
alpha = 0.05
power = 0.8
n2/n1 = 1
p1 p2 n1 n2
1 0.10 0.5 25 25
2 0.15 0.5 33 33
3 0.20 0.5 45 45
4 0.25 0.5 66 66
5 0.30 0.5 103 103
6 0.35 0.5 183 183
7 0.40 0.5 408 408
8 0.45 0.5 1605 1605
9 0.50 0.5 NaN NaN
10 0.55 0.5 1605 1605
11 0.60 0.5 408 408
12 0.65 0.5 183 183
13 0.70 0.5 103 103
14 0.75 0.5 66 66
15 0.80 0.5 45 45
16 0.85 0.5 33 33
17 0.90 0.5 25 25
Estimation of sample size for testing Ho: p1==p2==p
Assumptions:
alpha = 0.05
power = 0.8
p = 0.85
sig.diff = 0.05
Estimated required sample size:
n = 801
Total n = 1602
Estimation of sample size for testing Ho: p1==p2 == p
Assumptions:
alpha = 0.05
power = 0.8
p = 0.85
sig.inferior = 0.05
Estimated required sample size:
n = 631
Total n = 1262
Estimation of sample size in a cluster radomized controlled trial
for testing Ho: p1==p2
Assumptions:
alpha = 0.05
power = 0.8
p1 = 0.5
p2 = 0.3
n2/n1(ratio) = 1
Current mean cluster size = 350
Intra-cluster correlation coefficient = 0.15
Maximum expected cluster size = 500
Minimum expected cluster size = 250
Design Effect:Unadjusted = 53.35
Design Effect:Adjusted = 55.02411
Estimated required sample size:
When design effect is unadjusted for unequal cluster sizes
n1 = 5495
Number of clusters for n1 = 16
n2 = 5495
Number of clusters for n2 = 16
n1 + n2 = 10990
Total number of clusters = 32
When design effect is adjusted for unequal cluster sizes
n1 = 5667
Number of clusters for n1 = 16
n2 = 5667
Number of clusters for n2 = 16
n1 + n2 = 11334
Total number of clusters = 32
Lot quality assurance sampling
Method = Exact
Population size = 10000
Maximum defective sample accepted = 0
Probability of defect accepted = 0.02
Alpha = 0.05
Sample size required = 148
Lot quality assurance sampling
Method = Normal approximation
Population size = 10000
Alpha = 0.05
p0 q N n
1 0.01 0 10000 262
2 0.02 0 10000 131
3 0.03 0 10000 87
4 0.04 0 10000 65
5 0.05 0 10000 52
6 0.06 0 10000 43
7 0.07 0 10000 36
8 0.08 0 10000 32
9 0.09 0 10000 28
10 0.10 0 10000 25
```

epiDisplay documentation built on May 11, 2018, 1:04 a.m.

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