As the effect sizes and bar graphs in Table 1 indicate, the
findings across studies were highly consistent. Of the 111 individual
effect sizes, 102 were in the direction of a detrimental outcome
with 78 of these statistically significant. In contrast, nine of the
effect sizes were in the direction of a beneficial outcome but only
one (Tennant, Detels, & Clark, 1975) was statistically different
from zero. Thus, among the 79 statistically significant effect sizes,
99% indicated an association between spanking and a detrimental
child outcome.
Table 2 summarizes the mean weighted effect sizes and confidence
intervals for each outcome along with a Z test for significant
difference from zero and an I
2 statistic that estimates the amount of
variation in the mean weight effect size that was attributable to
underlying study heterogeneity. Spanking was significantly associated
with 13 of the 17 outcomes examined. In each case, spanking
was associated with a greater likelihood of detrimental child
outcomes. In childhood, parental use of spanking was associated
with low moral internalization, aggression, antisocial behavior,
externalizing behavior problems, internalizing behavior problems,
mental health problems, negative parent– child relationships, impaired
cognitive ability, low self-esteem, and risk of physical
abuse from parents. In adulthood, prior experiences of parental use
of spanking were significantly associated with adult antisocial
behavior, adult mental health problems, and with positive attitudes
about spanking. The remaining four meta-analyses were not significantly
different from zero. The 13 statistically significant mean
effect sizes ranged in size from .15 to .64. The overall mean
weighted effect size across all of the 111 study-level effect sizes
was d .33, with a 95% confidence interval of .29 to .38; this
mean effect was statistically different from zero, Z 14.84, p
.001.