Understand the relationship
The reasoning behind the result
Three operations answer three questions
Tcorrected = T − BT; Lcorrected = L − BL; r = Tcorrected/Lcorrected
Background subtraction removes the entered background contribution from each measurement. Within-lane normalization then divides corrected target signal by corrected loading-reference signal. Finally, comparison with the reference group puts those ratios on a common relative scale.
The loading reference may be a measured control protein or a measured total-protein lane signal, provided its use is justified by the experiment. The arithmetic cannot determine whether that reference is stable or whether the imaging response is linear.
Background must have the same signal meaning
If the band value is an integrated intensity over an area, its background contribution must also be integrated over that area. A mean background per pixel cannot be subtracted directly from an integrated band total without accounting for the area.
Corrected loading-reference signal must be positive. A zero corrected target is allowed and produces a zero ratio. Negative corrected targets are rejected here because dividing and interpreting them as nonnegative relative expression would obscure the measurement problem; the blank-correction tool can inspect signed differences separately.
The reference group defines one, not every reference lane
foldᵢ = rᵢ/r̄control; changeᵢ = (foldᵢ − 1) × 100%
Each lane is normalized before the mean reference ratio is calculated. The control-group mean is one on the final fold scale, but individual control lanes can remain above or below one. Forcing every control replicate to one would hide its variability.
A fold value of two means twice the normalized signal relative to the entered reference-group mean. A fold value of 0.5 means half that signal. These are descriptive comparisons, not proof of a treatment effect.
Replicates remain visible
Group summaries use the arithmetic mean of per-sample fold values, with sample standard deviation when at least two observations are supplied. The detailed table retains each corrected target, corrected reference and ratio so unequal loading can be inspected.
This workbench does not run hypothesis tests or infer whether observations are biological or technical replicates. It does not convert a signal ratio into an absolute protein concentration.
Follow the numbers
Why target signal alone can mislead
- Control lane C1: corrected target = 110 − 10 = 100; corrected loading reference = 60 − 10 = 50; ratio = 2.
- Control lane C2: corrected target = 210 − 10 = 200; corrected loading reference = 110 − 10 = 100; ratio = 2. The mean control ratio is 2.
- Treatment T1: corrected target = 210 − 10 = 200; corrected reference = 60 − 10 = 50; ratio = 4.
- Treatment fold = 4/2 = 2, a descriptive increase of 100% relative to the normalized control mean.
C2 and T1 have the same corrected target signal, but their different loading-reference signals produce different normalized ratios.
Quick guide
How to use this calculator
- Choose paired target/reference measurements or already-normalized assay signals.
- Enter unique sample names and group labels, then identify the reference group.
- Check corrected signals and the within-sample ratio before interpreting fold change.
- Compare individual replicates and group summaries. Technical replicates are not automatically independent biological samples.
Calculation method
Calculation and interpretation
Keep background subtraction, within-lane normalization and between-group comparison separate and inspectable.
rᵢ = (targetᵢ − target backgroundᵢ)/(referenceᵢ − reference backgroundᵢ); foldᵢ = rᵢ/mean(rcontrol)
Worked example
Why target signal alone can mislead
C2 and T1 have the same corrected target signal, but their different loading-reference signals produce different normalized ratios.
rᵢ = (targetᵢ − target backgroundᵢ)/(referenceᵢ − reference backgroundᵢ); foldᵢ = rᵢ/mean(rcontrol)
Supported inputs
Precision and limits
Measurement controls
Entered signals must have a suitable background correction and remain within the measurement system's established working range. Saturated or incompatible measurements cannot be repaired by a ratio.
Biological interpretation
A relative signal, absorbance ratio or calculated loading volume does not establish sample purity, gene expression, mechanism, statistical significance or experimental validity.
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