C

D

And

Sample size

198

158

200

Get to the bottom of the grades

17.25 (12.00 - 22.00)

16.60 (11.70 - 21.05)

20.40 (16.80 - 24.73)

Measured results

18.85 (13.93 - 23.50)

22.20 (17.26 - 26.03)

20.30 (16.33 - 24.58)

With

−6.800

−10.616

−0.403

P

<0.05

<0.05

0.687