Question

A researcher conducts a study and concludes that a new behavioral health treatment program significantly reduces one's risk for disease compared with risk levels in the general population (d = -0.64). Interpret the size of this effect.

A) 64% of the variability in risk level can be accounted for by the new treatment.

B) 64% of the new treatment can be accounted for by the risk levels.

C) Risk levels in the population shifted 0.64 standard deviations below the mean.

D) Risk levels in the population shifted 0.64 standard deviations above the mean.

Answer 1

Correct option: (C)

Explanation:

The Cohen's d effect size is a numerical quantity that represents the difference between two means.

The formula to compute the effect size is:

`d=(M_(1)-M_(2))/(SD_(pooled))`

The numerical value of the Cohen's d indicate the distance between the two means, i.e. it represents the standard deviation value by which the mean M₂ is away from M₁.

For example, d = 2 implies that M₂ is above 2 standard deviations of M₁.

The Cohen's d value computed in this case is,

d = -0.64.

The negative sign indicates that the risk levels in the population is less than the mean.

So, the value -0.64 implies that the risk levels in the population is 0.64 standard deviations below the mean.

Thus, the correct option is (C).