ELISA standards in duplicate: intra-assay CV
Eight duplicate standards from one assay run.
RSD Calculator
FigranPaste replicates for every sample to get %RSD or %CV, flags over your limit and a precision figure.
- Many samples at once
- Intra- and inter-assay CV
- Precision figure and methods text
8 samples · 2 replicates
Options
Intra-assay CV 1.70%
Mean of 8 samples · range 0.565–4.04% · 0 above 15% · sample SD (n − 1)
Results by sample
| Name | n | Mean | SD | %CV | Status |
|---|---|---|---|---|---|
| Std 0.0488 | 2 | 0.0175 | 0.0007 | 4.04% | Within limit |
| Std 0.195 | 2 | 0.1225 | 0.0021 | 1.73% | Within limit |
| Std 0.391 | 2 | 0.2105 | 0.0064 | 3.02% | Within limit |
| Std 0.781 | 2 | 0.3755 | 0.0021 | 0.565% | Within limit |
| Std 1.56 | 2 | 0.6115 | 0.0035 | 0.578% | Within limit |
| Std 3.13 | 2 | 1.0100 | 0.0127 | 1.26% | Within limit |
| Std 6.25 | 2 | 1.3490 | 0.0212 | 1.57% | Within limit |
| Std 12.5 | 2 | 1.7200 | 0.0141 | 0.822% | Within limit |
Summary
| Mean of CVs | 1.70% |
|---|---|
| RMS | 2.06% |
| Median | 1.42% |
| Samples | 8 |
| Range | 0.565–4.04% |
| Above limit | 0 / 8 · 15% |
| Standard deviation | Sample (n − 1) |
Report
Results
The mean intra-assay CV was 1.70% (range 0.565–4.04%, 8 samples); none exceeded 15%.
Methods
Intra-assay precision was expressed as the %CV of duplicate measurements, calculated as SD / mean × 100 using sample SD (n − 1).
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How to calculate RSD and CV
Go from replicate measurements to a precision figure in four steps.
1Paste your data
Enter one sample per row or paste a single column of values.
2Choose the run
Select one run for intra-assay or different runs for inter-assay precision.
3Review the results
Check each sample and any values above your limit.
4Export the figure
Download the figure or copy the report.
Intra-assay and inter-assay CV
Choose the precision measure that matches how the data were collected.
| Precision | Input | Calculation | Common limit |
|---|---|---|---|
| Intra-assay CV | Replicates from one run | CV for each sample, then average | < 10% |
| Inter-assay CV | One mean per run for each sample | CV for each sample, then average | < 15% |
| Intermediate precision | Intermediate precision accounts for variation across runs under ICH Q2(R2). A variance-components analysis can separate sources of variation; this calculator uses the simpler average of per-sample CVs described by Salimetrics. | ||
Mean or root mean square
For the default duplicate data, the mean CV is 1.70% and the RMS CV is 2.06%. RMS gives greater weight to large CVs.
Precision profile
Plot CV against mean concentration or signal to see how precision changes across the measurement range.
References: Reed et al. (2002) · Salimetrics · ICH Q2(R2) · ICH M10
RSD and coefficient of variation formula
Relative standard deviation and coefficient of variation are synonymous: divide the standard deviation by the mean and multiply by 100.
For the six HPLC injections, 3.13603 / 1522.63 × 100 = 0.206%.
References: IUPAC Gold Book · Hyslop & White (2009)
RSD calculator FAQ
Is RSD the same as the coefficient of variation?
Yes. %RSD and %CV both equal SD divided by the mean, multiplied by 100. RSD is common in analytical chemistry, while CV is common in immunoassays.
Should I use the sample or the population standard deviation?
Use sample SD for replicate measurements sampled from possible measurements. Use population SD only when the entire population was measured.
What %CV or %RSD is acceptable?
It depends on the method and its validation requirements. For chromatographic bioanalysis, ICH M10 specifies at most 15% CV, or 20% at the lower limit of quantification; ligand-binding assays have different limits. Set the limit required by your protocol. For ongoing QC monitoring, use the Levey-Jennings Chart Maker.
Should I calculate ELISA CVs from OD or concentration?
Use back-calculated concentration to report sample precision; OD CV describes repeatability of the plate reading. ELISA standard curve calculator.
How do I calculate %CV or %RSD in Excel?
Use =STDEV.S(A2:A7)/AVERAGE(A2:A7)*100. The same formula works in Google Sheets.
Why is the CV so high at low concentrations?
When the mean approaches zero while SD stays similar, CV increases. A precision profile makes that pattern visible. To investigate unusual observations, use the Outlier Calculator.
When should I not use the coefficient of variation?
Avoid CV for quantities without a meaningful true zero or on a logarithmic scale, including Celsius temperature, pH and qPCR Ct values. delta delta Ct calculator.
How many replicates do I need for %RSD?
At least two values are needed to compute sample SD, but the number needed for validation depends on the protocol. ICH Q2(R2) describes repeatability studies using nine determinations or six at the test concentration.
When should I report the CV instead of the standard deviation?
Use CV to compare relative variability across positive means; SD retains the original units. CV does not measure agreement between two methods. Bland–Altman plot.
Check the precision of your replicates
Calculate CVs and create a precision figure from your data.
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