2.3 Data processing
The raw data were prepared using the ‘affy’ package in the Bioconductor
project of the R software to obtain the expression values of the miRNA
and mRNA probe set, including background correction, normalization, and
summarization.10-12. Then, the self-written Perl
language script program was used to convert the expression value of the
mRNA probe set into the expression value of the gene (expressed by NCBI
Entrez Gene ID, http://www.ncbi.nlm.nih.gov/gene). Finally, array
were standardized, that is, the median expression value of all genes was
subtracted from the expression value of each gene for each sample, so
that the normalized miRNA and gene expression values were obtained. Only
genes exhibiting an expression level fold change (FC) >1.5,
or 1/FC<1.5 in the BPD group compared with that in the control
group, were considered to reveal altered expression levels and were
selected for further analysis.