Consider the following OLS multiple regression results from Sabia, Wang, and Cesur (2017). The data are from the National Longitudinal Study of Adolescent Health and the sample consists of students in grades 7 through 12. The dependent variable is each student's self-reported grade point average (GPA) on a 0 to 4-point scale. The explanatory variables are listed in the table below. The standard errors are in parentheses below each estimated coefficient. Dependent Variable : GPA Explanatory Variables Sleep hours 0.207 (0.027) Sleep hours squared -0.013 (0.002) Male -0.251 (0.013) Age -0.544 (0.060) Age squared 0.017 (0.002) Black -0.180 (0.016) Other ethnicity 0.122 (0.021) Hispanic -0.192 (0.022) Natural log of parental income 0.080 (0.010) Mother's education: high school 0.111(0.021) Mother's education: some college 0.242 (0.024) Mother's education: college 0.420 (0.023) Parents are married 0.115 (0.031) Parents are separated/divorced -0.020 (0.032) Urban residence -0.057 (0.014) Overweight or obese -0.110 (0.019) Diabetes -0.111 (0.129) Migraine -0.052 (0.022) Allergies 0.043 (0.014) Number of Observations 15,369