Moreover, the random selection test function is designed to randomly select the same number of genes as were originally extracted as biomarker candidates for a specific cancer.
For both the bootstrap test and the random selection test use here, the results were significant (p < 0.0001).
All random selection test and permutation test analyses were conducted in R. Permutation P-values for each CpG locus were calculated by assessing the number of significantly age-associated sites for each study under 100 age-permutated data sets.
During the predictor performance examination step, the Cox test is calculated with the clustered clinical outcome of distinct phenotypes and the random selection test can be performed for further validation to increase confidence that gene sets have not been selected randomly.
Furthermore, both the bootstrap test function and the random selection test produced significant results (p < 0.0001); the former was implemented in BRCA for examining the relationship between genes for clustering and the distinct phenotypes and the latter test was used for examining the significance of the predicted predictor using randomly selected genes for 1000 repetitions.
Interestingly, we found that our normal age-associated hypermethylated loci overlapped significantly with the previously reported bivalent regions (P = 3.08E 31 using a Z-test of 10,000 random selection tests; Additional file 2: Figure S11).
To increase the level of statistical confidence and for further validation of the relationship found between clustering genes and the phenotypes and the significance of the predictor, bootstrap and random selection tests can be performed, respectively.
The results showed that 15 CpG positions ("Conserved CpG" in Additional file 1: Table S2) had significantly higher conservation scores (average phyloP score > 1.3) and that this number was significantly higher than random expectations (P = 3.56E 09 from a Z test using the phyloP distribution of 10,000 random selection tests).
The correlation between the actual ages of the combined normal samples and their predicted ages using the model was highly significant (R = 0.91, P = 0.002 from 10,000 random selection tests using all loci in the platform; Figure 5A), which indicates that the DNAm levels of the age-associated signature sites can be used to predict the age of tissues, regardless of tissue type.
The sequences surrounding the normal signature showed significant overrepresentation of thymine (T) residues at -6, -3, +1, +6, +8, and +10 bases from the CpG loci (10,000 random selection tests of all CpG loci in the platform, P = 0.031, 0.036, 0.008, 0.036, 0.002, and 0.002, respectively), adenine (A) residues at +3 and +7 bases (P = 0.023, 0.035), and guanine (G) residues at -1 base (P = 0.04).
random selection of test persons, forming groups of equal or at least similar composition (= experimental group and control group), precise isolation of research-relevant variables, as well as.
