[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Epidemiology](https://durgical.com/en/epidemiology/) › [Biostatistics](https://durgical.com/en/epidemiology/areas/stats/) › Statistical vs clinical significance

# Statistical vs clinical significance

- Concept

A statistically significant result does not mean it matters to the patient. The size of the effect has to be checked.

Updated Nov 5, 2026

## Key points

- Statistical significance: p

## What it is

Statistical significance asks whether a difference is hard to explain by chance; clinical significance asks whether it is large enough to matter. With huge samples tiny effects reach very small p values, and with small samples important effects may miss significance. The minimal important difference (MID), the smallest change patients perceive as beneficial, is the benchmark for judging the confidence interval.

## Worked example

- Data: on a 0 to 100 point pain scale, the MID is 10 points. A very large trial enrols 10 000 people per group.
- Observed difference = 2 points, with SD = 20 in each group.
- SE = 20 × √(2 / 10 000) = 20 × 0.0141 = 0.28 points.
- z = 2 / 0.28 = 7.1, so p

| Result | Statistically significant? | Clinically important? | Example CI (MID = 10) |
| --- | --- | --- | --- |
| Small, precise effect | Yes | No | 1.4 to 2.6 |
| Large, precise effect | Yes | Yes | 12 to 18 |
| Uncertain effect | No | Unknown | −3 to 20 |
| No important effect | No | No | −2 to 3 |

## Markers

- MID
- 95% CI
- p

## Common pitfalls

- Announcing a treatment as effective only because p 0.05.
- Presenting only the relative risk reduction, which makes a small absolute benefit look large.

## Memory aid

‘Significant says it exists; important says it matters.’

## Test yourself

Think of the answer, then tap the question to see it.

## Why can a very small effect be statistically significant?

Because with very large samples the standard error is tiny, so any non-zero difference gives a small p value.

## What is the minimal important difference?

The smallest change in an outcome measure that patients perceive as beneficial and that would justify a change in management.

## A 95% CI for the difference runs from 1 to 3 points and the MID is 8. How is it read?

The effect is statistically significant (it excludes 0) but of little clinical importance: the whole interval lies below the MID.

## Which measures help judge the clinical importance of a trial?

The effect size with its CI, the absolute risk reduction and the number needed to treat, set against the MID.

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## Connections

## Related 5

- [P value](https://durgical.com/en/epidemiology/p-value/)
- [Confidence interval](https://durgical.com/en/epidemiology/confidence-interval/)
- [Sample size](https://durgical.com/en/epidemiology/sample-size/)
- [Number needed to treat](https://durgical.com/en/epidemiology/number-needed-to-treat/)
- [Absolute risk reduction](https://durgical.com/en/epidemiology/absolute-risk-reduction/)

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Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.

Sources: [Chapter 15: Interpreting results and drawing conclusions](https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-15) (Cochrane, 2024); [What is the relationship between a test and a confidence interval?](https://www.itl.nist.gov/div898/handbook/prc/section1/prc15.htm) (NIST/SEMATECH e-Handbook of Statistical Methods, National Institute of Standards and Technology, 2012).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/statistical-vs-clinical-significance/