Prediction interval for a difference of scores in a 2-group experiment

Source: R/statpsych1.R

For a 2-group experimental design, this function computes a prediction interval for how the response variable score for one randomly selected person from the study population would differ under the two treatment conditions. Both equal variance and unequal variance prediction intervals are computed.

pi.score2(alpha, m1, m2, sd1, sd2, n1, n2)

Arguments

alpha

alpha level for 1-alpha confidence

m1

estaimted mean for group 1

m2

estimated mean for group 1

sd1

estimated standard deviation for group 1

sd2

estimated standard deviation for group 2

n1

sample size for group 1

n2

sample size for group 2

Value

Returns a 2-row matrix. The columns are:

  • Predicted - predicted difference in scores

  • df - degrees of freedom

  • LL - lower limit of the prediction interval

  • UL - upper limit of the prediction interval

References

Hahn GJ (1977). “A prediction interval on the difference between two future sample means and its application to a claim of product superiority.” Technometrics, 19(2), 131--134. ISSN 0040-1706, doi:10.1080/00401706.1977.10489520 .

Examples

pi.score2(.05, 29.57, 18.35, 2.68, 1.92, 40, 45)
#>                              Predicted       df       LL       UL
#> Equal Variances Assumed:         11.22 83.00000 4.650454 17.78955
#> Equal Variances Not Assumed:     11.22 72.34319 4.603642 17.83636

# Should return:
#                              Predicted       df       LL       UL
# Equal Variances Assumed:         11.22 83.00000 4.650454 17.78955
# Equal Variances Not Assumed:     11.22 72.34319 4.603642 17.83636