A peptide experiment can look convincing when three wells give almost the same result. The next question is whether those wells represent three separate tests of the biological effect, or three measurements within one test. That difference changes what the result can support.
First, say what was repeated
A technical replicate repeats a measurement or assay step under closely shared conditions. In the cell-culture example discussed by Nature’s guidance, different wells cultured and tested together on one plate are technical replicates, not distinct biological sources. A biological replicate addresses variation between the independent biological units specified by the design. Nature’s replicate guidance asks researchers to distinguish the two and define what n means.
For a reader, the useful question is simple: could these results all share the same preparation error or biological starting material? If they could, closely matching numbers do not by themselves show that the effect will repeat with independent material.
A counting example: nine readings, not automatically n = 9
Imagine a study with three independently planned runs and three wells in each run. There are 3 × 3 = 9 well readings. The nine readings are nested within three runs. They should not be described as nine independent biological experiments just because each well produced a number.
| Run | Technical well readings | What to retain |
|---|---|---|
| 1 | 3 | All readings plus the run identifier |
| 2 | 3 | All readings plus the run identifier |
| 3 | 3 | All readings plus the run identifier |
This is an invented counting example, not study data or an NHD experiment. Separate days alone do not establish biological independence; the cell source, preparation and design determine the experimental unit. A suitable analysis must account for that structure.
Check the label beside a small error bar
A small error bar may describe variation among wells, rather than variation among independent experiments. Read the figure legend before interpreting it. Ask whether the displayed spread is a standard deviation, a standard error or a confidence interval, and whether it was calculated at the appropriate level. Do not select the description that makes the graph look most certain.
Keep the peptide record with the experiment
When comparing LL-37 or KPV experiments, retain the exact compound, supplied form, lot identifier if available, amount basis, assay medium and control conditions. Changing the material and the experimental design together makes the source of a difference harder to identify.
For laboratory procurement, review the LL-37 and KPV catalog records. Choose the material required by the protocol; the catalog is not evidence that an experimental effect has been reproduced. Send a research enquiry with the identity, amount basis and records you need.
A useful sentence for a methods section
State the number of independent units, the number of technical measurements per unit and how those measurements entered the analysis. If a result is representative of several runs, retain the data for the other runs as well. NIH’s preclinical reporting principles emphasize clear reporting of repetitions and experimental sample size.
Research material only. This guide explains experimental reporting and does not provide human or veterinary use instructions.
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