Using the Quarterly Compound Fractional Grey Model to Predict the Air Quality in 22 Cities of China

Table 4

The fitting results of the two models (unit: μg/m³).

Quarter	Actual value	GM (1, 1)	QCGM (1, 1)	New sequence	GM (1, 1)	QCGM (1, 1)
2015-1	68	68	68	75	75	75
2015-2	54	60	54	54	60	49
2015-3	50	59	49	50	59	42
2015-4	68	59	69	68	59	65
2016-1	61	58	66	61	58	67
2016-2	52	58	54	52	58	56
2016-3	47	57	48	47	57	51
2016-4	73	57	67	73	57	72
2017-1	68	56	64	68	56	69
2017-2	56	56	52	56	56	55
2017-3	50	55	46	50	55	48
2017-4	61	55	64	61	55	66
2018-1	56	54	60	56	54	62
2018-2	49	54	49	49	54	48
2018-3	41	53	43	41	53	42
2018-4	60	53	60	60	53	56
2019-1	56	52	57	56	52	52
2019-2	44	52	46	44	52	40
2019-3	42	51	41	42	51	34
2019-4	59	51	56	59	51	46