Normalization of expression data
75 percentile level
Each expression data is applied to (1) 75 percentile
normalization, and (2) log2 transformation.
When all expression data are arranged in increasing
order, the expression level corresponding to 75% of
the distribution.
Histogram of signal intensity
Raw data before normalization
After normalization
Adjust to the right
75
%
75%
75％
25％
75%
75
%
75 percentile
Adjust to the left
75
%
75%
Normalization is done by adjusting
each expression data to a 75
percentile baseline.
Expression
level
The expression profile (signal intensity value) is presented in 2 graphs.
Raw signal intensity
Normalized signal intensity
Normalized signal intensity
Log2 scale
Raw signal intensity
Sample ID
3 replicates
Sample ID
Highest value among triplicates
Replicate 1
Replicate 2
Median
Replicate 3
Lowest value among triplicates
Note that even if there is a difference in absolute expression values, there are cases when the
difference may not be reflected in normalized expression values.
Raw data before normalization
Normalized expression value
Adjust to the right
A
A
75
%
B
75%
B
75
%
75%
Adjust to the left
C
C
75
%
75%
Normalization
A
B
C
A
B
C
Samples with insufficient amount of labelled cRNA usually showed weak signal
intensity (See Sample list)。