The main output for this example is below, and we can obtain the effect size as Cohen's d = −0.950 [−1.868,−0.008]. This means that reading the self-help book reduced relationship happiness by about one standard deviation, which is a fairly massive effect. Note that the corresponding p-value is dangerously close to the conventional level of 0.05 though, so this result should be taken with a grain of salt.
| 95% CI for Mean Difference | 95% CI for Cohen's d | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| t | df | p | Mean Difference | SE Difference | Lower | Upper | Cohen's d | SE Cohen's d | Lower | Upper | |||||||||||||
| happy | -2.125 | 17.676 | 0.048 | -4.200 | 1.977 | -8.358 | -0.042 | -0.950 | 0.495 | -1.868 | -0.008 | ||||||||||||
| Note. Welch's t-test. | |||||||||||||||||||||||
On average, the reported relationship happiness after reading Marie Claire (M = 24.20, SE = 1.49), was significantly higher than after reading Women are from X and men are from Y (M = 20.00, SE = 1.30), t(17.68) = −2.125, p = 0.048, 𝑑^=−0.950[−1.868,−0.008].
| Group | N | Mean | SD | SE | Coefficient of variation | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| happy | Women are from X, Men are from Y | 10 | 20.000 | 4.110 | 1.300 | 0.205 | |||||||
| Marie Claire | 10 | 24.200 | 4.709 | 1.489 | 0.195 | ||||||||