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MCID and MDC Calculator

Enter a baseline and a retest and the calculator works out the change, then says whether it clears the measurement error (MDC) and the smallest change that matters to a client (MCID) for the population you pick. It runs in your browser and shows only thresholds that have been checked against their primary paper.

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The calculator is free and needs no sign-in. Nothing you type into it is sent anywhere, saved anywhere or counted anywhere.

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MDC and MCID: what each one means

The minimal detectable change, or MDC, is the smallest change larger than the error in the measurement itself. A change below the MDC may be the test rather than the client.

The minimal clinically important difference, or MCID, is the smallest change a client would notice as worthwhile. It is estimated from a study population, usually by asking participants whether they felt better and finding the change that best separates those who did from those who did not.

Both are estimates about groups. Neither decides anything about one person in front of you.

How MDC is calculated

The MDC is derived from the standard error of measurement. A paper reporting an MDC at 95% confidence multiplies the standard error of measurement by 1.96 and by the square root of 2, which comes out near 2.77 times the standard error.

epnote does not calculate a threshold itself. Every number the calculator shows was read from the paper that reported it and checked against it, and the calculator does the comparison, not the estimation.

Why thresholds differ by population

A threshold is a property of the population it was measured in, not of the test. A minimal detectable change measured after total hip replacement does not transfer to a client with a stroke, and the calculator will not pretend it does: it matches on the population you pick, and says it has nothing when there is no verified row for that pairing.

This is also why some pairings are empty. Of the 83 rows in epnote's evidence registry, 57 have been checked against their primary paper. The other 26 are not used: 17 because the paper could not be opened to confirm the figure, 6 because the authors themselves said the number was not a reliable estimate for that group, and 2 because they were relabelled rather than cleared.

Writing change in a report

  • Give the baseline and the current value, with the unit in words.
  • Put the change in daily life before the number.
  • If you name a threshold, name the population it was measured in and the paper it came from.
  • Do not turn a threshold into a verdict. State the change, state the threshold it is being compared against, and let the reader see both.

Which measures have verified thresholds

The calculator lists every core measure and every population in the registry, and tells you when a pairing has nothing verified. The measures library on this site shows the same thresholds per measure, with their citations.

Questions

What is the difference between MDC and MCID?
The MDC is the smallest change larger than measurement error, so it tells you whether a change is real. The MCID is the smallest change a client would notice as worthwhile, so it tells you whether a real change matters. A change can clear one and not the other.
How do you calculate MDC95?
From the standard error of measurement: multiply it by 1.96 and by the square root of 2, which is about 2.77 times the standard error. epnote does not calculate thresholds; it reads the value the paper reported and compares your change against it.
Can the MDC replace the MCID?
They answer different questions, so no. A change that clears the MDC is probably real; whether it matters to the client is the MCID's question.
What if no MCID exists for my client's population?
The calculator says so rather than borrowing a number from a different population. Report the change itself, name the measure and the baseline, and leave the threshold out.
How should I report a change smaller than the MDC?
Report it as the measurement it is, and say that it is within the measurement error of the test. That is more useful to a reader than leaving it out.

Write this report in epnote, free

epnote is report software for Australian exercise physiologists. Enter your measurements once and it works out the change and lays the report out, ready to sign. What you write about a client stays on your device.

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Sources

Everything on this page comes from one of these. epnote writes nothing clinical from memory.

  • epnote threshold verification pack, 25 October 2026, and the 57 rows cleared from it on 26 October 2026docs/research/2026-10-25-threshold-verification.md
  • epnote evidence registry: 83 rows, each with its citation, population, method and verification statedata/evidence/

What this page does not cover yet

  • The brief asks for a generic MDC95 mode that takes a standard error of measurement or an ICC for any measure. That mode is not built: it would invite a clinician to type a figure from elsewhere and get a threshold back, which is the opposite of what the verified registry is for.
  • The brief's slug is /resources/tools/mcid-mdc-calculator and the calculator itself lives at /tools/mcid-calculator, which was built and published earlier. This page is the library's entry for it rather than a second copy.

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