Answer:
The psychologist finds that the estimated Cohen's d is 0.583.
Step-by-step explanation:
The Cohen's d is used to calculate the effect size, appied when a null hypothesis is rejected.
It can be calculated for this case of population mean as:
[tex]d=\dfrac{M-\mu}{\sigma}=\dfrac{6.5-5.8}{1.2}=\dfrac{0.7}{1.2}=0.583[/tex]
The psychologist finds that the estimated Cohen's d is 0.583.