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Confidence interval for a linear contrast of means in a between-subjects design

Source: R/statpsych1.R
ci.lc.mean.bs.Rd

Computes a test statistic and confidence interval for a linear contrast of means in a between-subjects design. This function computes both unequal variance and equal variance confidence intervals and test statistics. A Satterthwaite adjustment to the degrees of freedom is used with the unequal variance method.

For more details, see Section 3.3 of Bonett (2021, Volume 1)

Usage

ci.lc.mean.bs(alpha, m, sd, n, v)

Arguments

alpha

alpha level for 1-alpha confidence

m

vector of estimated group means

sd

vector of estimated group standard deviations

n

vector of sample sizes

v

vector of between-subjects contrast coefficients

Value

Returns a 2-row matrix. The columns are:

  • Estimate - estimated linear contrast

  • SE - standard error

  • t - t test statistic

  • df - degrees of freedom

  • p - two-sided p-value

  • LL - lower limit of the confidence interval

  • UL - upper limit of the confidence interval

References

Snedecor GW, Cochran WG (1989). Statistical Methods, 8th edition. ISU University Pres, Ames, Iowa.

Bonett DG (2021). Statistical Methods for Psychologists https://dgbonett.sites.ucsc.edu/.

Examples

m <- c(24.9, 23.1, 16.4)
sd <- c(5.21, 4.67, 4.98)
n <- c(30, 30, 30)
v <- c(.5, .5, -1)
ci.lc.mean.bs(.05, m, sd, n, v)
#>                              Estimate       SE      t    df p       LL       UL
#> Equal Variances Assumed:          7.6 1.108703 6.8549 87.00 0 5.396332 9.803668
#> Equal Variances Not Assumed:      7.6 1.111135 6.8399 57.59 0 5.375484 9.824516

# Should return:
#                              Estimate       SE      t    df p       LL       UL
# Equal Variances Assumed:          7.6 1.108703 6.8549 87.00 0 5.396332 9.803668
# Equal Variances Not Assumed:      7.6 1.111135 6.8399 57.59 0 5.375484 9.824516

m <- c(33.5, 37.9, 38.0, 44.1)
sd <- c(3.84, 3.84, 3.65, 4.98)
n <- c(10, 10, 10, 10)
v <- c(.5, .5, -.5, -.5)
ci.lc.mean.bs(.05, m, sd, n, v)
#>                              Estimate       SE      t    df       p        LL
#> Equal Variances Assumed:        -5.35 1.300136 -4.115 36.00 0.00022 -7.986797
#> Equal Variances Not Assumed:    -5.35 1.300136 -4.115 33.52 0.00024 -7.993588
#>                                     UL
#> Equal Variances Assumed:     -2.713203
#> Equal Variances Not Assumed: -2.706412

# Should return:
#                              Estimate       SE      t    df       p 
# Equal Variances Assumed:        -5.35 1.300136 -4.115 36.00 0.00022 
# Equal Variances Not Assumed:    -5.35 1.300136 -4.115 33.52 0.00024 
#                                     LL        UL
# Equal Variances Assumed:     -7.986797 -2.713203
# Equal Variances Not Assumed: -7.993583 -2.706417