Condom use in the Solomon study of Kvalem et al. (1996)

The number of students who used condoms at their most recent intercourse, at the 6-month posttest, among students who had had intercourse before the intervention, in each Solomon group of a school-based sex-education trial (Kvalem et al., 1996, p. 42). Numbers reported in the publication are reused with citation.

Usage

kvalem1996

Format

A data frame with 4 rows, one per Solomon group, and 5 variables:

group: The Solomon group.
pretested, treat: Indicators (1 = yes).
events: Students who used condoms at their most recent intercourse.
n: Students in the group with intercourse before the intervention who answered the 6-month posttest.

Source

Kvalem, I. L., Sundet, J. M., Rivø, K. I., Eilertsen, D. E., & Bakketeig, L. S. (1996). The effect of sex education on adolescents' use of condoms: Applying the Solomon four-group design. Health Education Quarterly, 23(1), 34–47. https://doi.org/10.1177/109019819602300103

Details

Design and caveats. Whole classes were randomized: 30 classes to the intervention, 15 of them pretested, and 94 to control, 47 of them pretested (p. 38). The authors analyzed individuals rather than classes because class sizes varied too much for a class-level analysis (p. 39). These counts are therefore individual-level, and analyses of them ignore the clustering; see perm_solomon() for cluster-level inference when class membership is available.

Known result. Fisher's exact and chi-square comparisons by fisher_solomon() reproduce the reported pattern: 70% (51/73) against 51% (76/148) among pretested students, chi-square = 6.85, and 43% (21/49) against 52% (69/133) among unpretested students, chi-square = 1.17 (p. 42).

Examples

# One row per student.
students <- kvalem1996[rep(seq_len(4), kvalem1996$n), c("pretested", "treat")]
students$used <- unlist(Map(function(e, n) rep(1:0, c(e, n - e)),
                            kvalem1996$events, kvalem1996$n))
with(students, fisher_solomon(used, treat, pretested))
#> Historical categorical Solomon analysis (El Karkri et al., 2025b)
#> 
#>    Condition Events (T) n (T) Events (C) n (C) Chi-square Fisher p
#>    Pretested         51    73         76   148       6.85   0.0095
#>  Unpretested         21    49         69   133       1.17   0.3180
#>     Combined         72   122        145   281       1.88   0.1922
#> 
#> Historical rule (significant among pretested, not among unpretested, alpha = 0.05): sensitization declared
#> Caution: this rule compares significance, not effects, and is not a test of
#> the Pretest x Treatment interaction. See marginal_solomon().