Table 4. Robust linear regression of Eq. 1. Uncorrected standard errors are reported for comparison only. Last column shows degrees of freedom.

		Estimate	Std. Errors	Robust std. errors	t-value	p-value	samples	df
Q1	β0	−176.46	14.98	15.55	−11.35	< 2.2 × 10−16	192	190
	β1	0.97	0.02	0.1	9.57	< 2.2 × 10−16
Q2	β0	35.33	12.6	12.9	2.74	0.007	192	190
	β1	0.27	0.05	0.09	2.89	0.004
Q3	β0	−1321.5	828.2	853	−1.55	0.12	192	190
	β1	0.83	0.05	0.1	6.25	2.7 × 10−9
Q4	β0	−146.3	23.2	23.7	−6.2	3.8 × 10−9	192	190
	β1	0.6	0.01	0.03	18.8	< 2.2 × 10−16
Q5	β0	6.8	14.8	15.1	0.5	0.66	188	186
	β1	0.4	0.04	0.1	3.72	0.0003
Q6	β0	−821	103	1387	−0.6	0.55	188	186
	β1	0.46	0.02	0.03	15.3	< 2 × 10−16