Final answer:
A non-significant result in a study with a treatment and a control group suggests a small Cohen's d value, likely below 0.2, since the effect size is not large enough to be statistically significant.
Step-by-step explanation:
If a study with treatment and control groups produces a non-significant result, the value for Cohen's d is likely to be small. A non-significant result suggests that there is not a large difference between the two groups.
Considering Cohen's standards for effect sizes, a reasonable value for Cohen's d in this scenario would be below 0.2, which is considered a small effect size. This is because any value above 0.2 would suggest a small effect, above 0.5 a medium effect, and above 0.8 a large effect. Since the result is non-significant, the effect size is likely closer to zero, indicating that the treatment had little to no effect when compared to the control group.