Aging effects on DNA methylation modules in human brain and blood tissue

Table 2 Analysis of variance of variance

Source of variation		ave.kME.green, total proportion of variance explained = 15.8%				logPvalue Stouffer, total proportion of variance explained = 6.7%
Source	Degrees of freedom	Sums of Sq	Proportion of total variance	F statistic	P-value (F-test)	Sums of Sq	Proportion of total variance	P-value (F-test)
PCG (Suz12+Eed+H3K27me3) OccupancyCount	1	49.35	0.071	2013.0	< 2.2E-16	82,530	0.050	< 2.2E-16
CPG_Island	2	50.78	0.073	1035.7	< 2.2E-16	24,867	0.015	< 2.2E-16
X chromosome	1	9.74	0.014	397.4	< 2.2E-16	764	0.000	5.5E-04
Distance to TSS	1	3.50E-01	0.001	14.1	1.7E-04	1,827	0.001	9.3E-08
Residual error	23,903	586.02	0.842			1,529,855	0.933
Total variation		696.24				1,639,843

The first six columns detail the sources of variation on ave.kME with respect to the green (aging) module. Polycomb group occupancy count explains the highest proportion of the total variance followed by CpG island status (inside, outside, and shore). Comparing the results from ANOVA applied to average kME with those from applying it to the logP-value (significance measure resulting from Stouffer's meta-analysis) reveals marked differences in the proportion of variance explained (15.8% versus 6.7%), which suggests again that the average kME measure is biologically more meaningful than the meta-analysis P-value. TSS, transcription start site.

ISSN: 1474-760X