# What a difference has to be before a person would notice it

Source: https://onco.cc/technologies/rejuv-measure-minimally-important-difference/  
OnCo record `rejuv-measure-minimally-important-difference` (Technology). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A trial can report a statistically significant change in a quality of life score that no person would notice. The minimally important difference is the attempt to say how much a score has to move to correspond to something a patient would call a change, and it differs by questionnaire, by scale, by cancer and by direction.

## Summary

The founding study asked patients directly. Osoba and colleagues gave people on chemotherapy for breast cancer or small-cell lung cancer a subjective significance questionnaire alongside the QLQ-C30, asking them to rate perceived change since they last completed it on a seven-category scale from much worse through no change to much better. The result: "For patients who indicated 'no change' in the SSQ, the mean change in scores in the corresponding QLQ-C30 domains was not significantly different from 0. For patients who indicated 'a little' change either for better or for worse, the mean change in scores was about 5 to 10; for 'moderate' change, about 10 to 20; and for 'very much' change, greater than 20." That five-to-ten-point rule of thumb is still the most quoted figure in the field.

The EORTC then did it the other way round, from the literature and from expert judgement. Cocks and colleagues had 34 experts, blinded to the actual results, predict differences across 2,217 contrasts from 152 articles, then combined the real data meta-analytically. Their conclusion is scale-dependent: "the recommended minimum to detect medium differences ranges from 9 (cognitive functioning) to 19 points (role functioning)". Role functioning needs the largest change to be meaningful, which is consistent with it being the least reliable scale on the instrument.

The modern approach is anchor-based and disease-specific, and the EORTC has published separate guidance for several cancers. In advanced breast cancer, using clinical anchors such as performance status, "MIDs for within-group change ranged from 5 to 14 points (improvement) and -14 to -4 points (deterioration), and MIDs for between-group change over time ranged from 4 to 11 points and from -18 to -4 points", with correlation-weighted values for most scales between 4 and 10 points. Equivalent guidance exists for lung cancer and malignant pleural mesothelioma and for prostate cancer.

Five things follow that a reader should hold on to.

The number is not symmetric. It takes a different amount of change to count as a deterioration than as an improvement, which the advanced breast cancer estimates show directly.

The number is not transferable. A threshold derived in advanced breast cancer does not apply to early prostate cancer, and the published sets differ.

Group differences and individual change are different quantities. The amount by which two trial arms must differ on average is not the amount by which one person's score must move for them to notice, and the second is usually larger. The FACT-Cog work makes the distinction explicit, separating clinically important differences for groups from meaningful change thresholds for individuals.

Stating the threshold in advance is what makes it work. The PRO-TECT trial declared its own and reported honestly against them: physical function with a stated minimum clinically important difference of 2 to 7 points, and "no MCID defined for symptom control or HRQOL". The mean differences it found were about 2.5 points on a 0 to 100 scale, and the authors reported them as such rather than calling them large.

A threshold can be gamed. If the pre-specified difference is chosen after seeing the data, or the largest published value is quoted for a negative result and the smallest for a positive one, the device stops working. Pre-specification is the only defence and is not universal.

## Fields

- Kind: Technology
- Status: established
- Last checked: 2026-10-02
- Tags: rejuvenation; survivorship; measurement; instruments
- Principle: Anchor-based methods estimate how much a score changes in people who report a small but definite change on an external criterion; distribution-based methods use a fraction of the standard deviation or the standard error of measurement. Anchor-based estimates are preferred because they are tied to something a person said, and distribution-based estimates are used to check them.
- Since: 1998
- Strengths: Turns a statistically significant result into a statement about whether anyone would notice; Disease-specific, anchor-based guidance now published for the QLQ-C30 in several cancers; Separates group-level differences from individual change thresholds
- Limitations: Different in each direction, each scale, each cancer and each estimation method; Not published for every instrument or every population; Easy to misuse by selecting the convenient published value after the fact; Regression to the mean shrinks anchor-based estimates, a known bias in the method

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Minimal_important_difference
- Osoba et al., Interpreting the significance of changes in health-related quality-of-life scores (JCO 1998): https://doi.org/10.1200/JCO.1998.16.1.139
- Cocks et al., Evidence-based guidelines for determination of sample size and interpretation of the EORTC QLQ-C30 (JCO 2011): https://doi.org/10.1200/JCO.2010.28.0107
- Musoro et al., Minimally important differences for interpreting EORTC QLQ-C30 scores in patients with advanced breast cancer (JNCI Cancer Spectrum 2019): https://doi.org/10.1093/jncics/pkz037
- Koller et al., Minimally important differences of EORTC QLQ-C30 scales in patients with lung cancer or malignant pleural mesothelioma (Lung Cancer 2022): https://doi.org/10.1016/j.lungcan.2022.03.018
- Gamper et al., Minimally important differences for the EORTC QLQ-C30 in prostate cancer clinical trials (BMC Cancer 2021): https://doi.org/10.1186/s12885-021-08609-7
- Bell et al., Important differences and meaningful changes for the Functional Assessment of Cancer Therapy-Cognitive Function (FACT-Cog) (J Patient Rep Outcomes 2018): https://doi.org/10.1186/s41687-018-0071-4
- Basch et al., Effect of electronic symptom monitoring on patient-reported outcomes among patients with metastatic cancer: the PRO-TECT randomized clinical trial (JAMA 2022): https://doi.org/10.1001/jama.2022.9265

## Connected records

- technologies: [Asking people how they are, every week, as a treatment in its own right](https://onco.cc/technologies/rejuv-measure-epro-as-treatment/), [BREAST-Q and the Q-portfolio: measuring what an operation left behind](https://onco.cc/technologies/rejuv-measure-breast-q/), [EORTC QLQ-C30: the questionnaire most cancer trials use](https://onco.cc/technologies/rejuv-measure-eortc-qlq-c30/), [EQ-5D: health reduced to one number, and what that number is for](https://onco.cc/technologies/rejuv-measure-eq-5d/), [FACT-G and the FACIT family: the other main questionnaire](https://onco.cc/technologies/rejuv-measure-fact-and-facit/), [How recovery is measured: the questionnaires behind the numbers](https://onco.cc/technologies/rejuv-measure-patient-reported-outcomes/), [Measuring lymphoedema: tape, bioimpedance and the quality of life scales](https://onco.cc/technologies/rejuv-measure-lymphoedema/), [Measuring memory and concentration after treatment](https://onco.cc/technologies/rejuv-measure-cognitive-function/), [The questionnaires that were never returned, and the people never asked](https://onco.cc/technologies/rejuv-measure-missing-data-and-who-is-not-asked/)
- cancers: [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Mesothelioma](https://onco.cc/cancers/mesothelioma/), [Non-small-cell lung cancer](https://onco.cc/cancers/nsclc/), [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Recovery & Rejuvenation](https://onco.cc/fronts/rejuvenation/), [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- terms: [Placebo](https://onco.cc/terms/placebo/), [Quality of life](https://onco.cc/terms/quality-of-life/)
- bottlenecks: [Failures are hidden](https://onco.cc/bottlenecks/b-negative-results/), [Patients lack understanding, navigation and agency](https://onco.cc/bottlenecks/b-patient-voice/), [Trial design, endpoints and cost](https://onco.cc/bottlenecks/b-trial-design/)

---
JSON: https://onco.cc/api/v1/entities/rejuv-measure-minimally-important-difference.json