meta: nnt – R documentation

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nnt

Calculate the number needed to treat (NNT)

Description

Calculate the number needed to treat (NNT) from estimated risk difference, risk ratio, or odds ratio, and a baseline risk.

Usage

nnt(x, ...)

## S3 method for class 'meta'
nnt(x, p.c, comb.fixed = x$comb.fixed, comb.random = x$comb.random, ...)

## Default S3 method:
nnt(x, p.c, sm, lower, upper, ...)

## S3 method for class 'nnt.meta'
print(
  x,
  comb.fixed = x$comb.fixed,
  comb.random = x$comb.random,
  digits = gs("digits"),
  digits.prop = gs("digits.prop"),
  big.mark = gs("big.mark"),
  ...
)

Arguments

`x`	An object of class `meta`, or estimated treatment effect, i.e., risk difference(s), risk ratio(s), or odds ratio(s).
`...`	Additional arguments (ignored at the moment).
`p.c`	Baseline risk (control group event probability).
`comb.fixed`	A logical indicating whether NNTs should be calculated based on fixed effect estimate.
`comb.random`	A logical indicating whether NNTs should be calculated based on random effects estimate.
`sm`	Summary measure.
`lower`	Lower confidence interval limit.
`upper`	Upper confidence interval limit.
`digits`	Minimal number of significant digits, see `print.default`.
`digits.prop`	Minimal number of significant digits for proportions, see `print.default`.
`big.mark`	A character used as thousands separator.

Details

The number needed to treat (NNT) can be easily computed from an estimated risk difference (RD), risk ratio (RR), or odds ratio (OR) and a given baseline risk (Higgins & Green, 2011, section 12.5).

Accordlingly, this function can be used to calculate NNTs for meta-analyses generated with metabin or metagen if argument sm was equal to "RD", "RR", or "OR". It is also possible to directly provide estimated treatment effects without conducting a meta-analysis (see Examples).

The baseline risk can be specified using argument p.c. If this argument is missing, the minimum, mean, and maximum of the control event probabilities in the meta-analysis are used for metabin; otherwise the control event probabilities 0.1, 0.2, ..., 0.9 are used.

Author(s)

Guido Schwarzer sc@imbi.uni-freiburg.de

References

Higgins, J.P.T and S. Green (2011): Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0 [Updated March 2011]. The Cochrane Library: http://www.cochrane-handbook.org

Examples

# Calculate NNT for RD = -0.21
# (Cochrane Handbook, version 5.1, subsection 12.5.4.1)
nnt(-0.21, sm = "RD")

# Calculate NNT for RR = 0.92 and baseline risk p.c = 0.3
# (Cochrane Handbook, version 5.1, subsection 12.5.4.2)
nnt(0.92, p.c = 0.3, sm = "RR")

# Calculate NNT for OR = 0.73 and baseline risk p.c = 0.3
# (Cochrane Handbook, version 5.1, subsection 12.5.4.3)
nnt(0.73, p.c = 0.3, sm = "OR")

# Use Mantel-Haenszel odds ratio to calculate NNTs
data(Olkin1995)
m1 <- metabin(ev.exp, n.exp, ev.cont, n.cont, data = Olkin1995,
              comb.random = FALSE)
nnt(m1, comb.random = TRUE)

nnt