HCAT's evidence base spans 60+ peer-reviewed studies across 20+ countries — from the tool's development and independent validations to adaptations, translations, and applications in hospitals, general practice and national systems. This page lists them all.
Development and reliability testing of HCAT on a national sample of NHS hospital complaints. HCAT reliably codes seven problem categories at four severity levels, plus stage of care and harm — “not only the first reliable tool for coding complaints… the first tool to measure the severity of complaints”. Free to download and use.
Gillespie & Reader (2016), BMJ Quality & Safety
Analysis of 1,110 HCAT-coded complaints from 56 NHS trusts showed how aggregated complaints reveal “hot spots” where harm clusters onto stages of care, and “blind spots” other monitoring misses: problems at admission and discharge, systemic problems, and errors of omission. Benchmark data and analysis scripts are downloadable as supplementary files.
Gillespie & Reader (2018), The Milbank Quarterly
Across 59 NHS hospital trusts, the severity of clinical problems in HCAT-coded complaints was the only patient-generated measure associated with hospital-level mortality — and it explained variance beyond staff-generated data, while staff incident-report rates showed no association at all. Patients provide valid, supplementary data on unsafe care.
Reader & Gillespie (2021), Journal of Applied Psychology
A national study of 641 complaints from 16 Irish public hospitals reproduced the UK hot-spot and blind-spot patterns almost exactly, with very high coding reliability (Gwet's AC1 = 0.93). Evidence that HCAT transfers across healthcare systems.
O'Dowd et al. (2022), International Journal for Quality in Health Care
Odense University Hospital analysed 6,366 complaints (13,156 problems) with disproportionality analysis borrowed from pharmacovigilance, ranking where problems cluster across departments. Hospital management then adopted HCAT for all complaints from 2022 — “likely… the world's largest sample of HCAT-scored complaints”.
Bogh et al. (2023), International Journal for Quality in Health Care
The first study to quantify how many negative experiences never become complaints: for every problem in a filed maternity complaint, between 4.8 and 13 more went unreported, depending on the issue. Formal complaints are the tip of an iceberg — and low-harm problems are the most under-reported.
Clausen et al. (2025), Acta Obstetricia et Gynecologica Scandinavica
Complaint volumes are rising faster than teams can read them. In 2023–24 the NHS in England received 241,922 complaints — up 37% since 2013–14 — and, at an hour per complaint, manually analysing a single year's complaints would take roughly 35,000 hours, or about 95 staff-years (Reader, 2025). Can AI help? Two independent 2025 studies tested large language models against trained human HCAT coders, with convergent results. Bunt et al. (2025) found GPT-4o only moderately valid on HCAT harm coding (weighted κ 0.49–0.57, against a human ICC of 0.86), systematically overestimating harm. Koh et al. (2025) tested three LLMs against HCAT(GP) coding in Singapore primary care: substantial agreement on domain (κ ≈ 0.62), but poor agreement on severity and harm (κ 0.11–0.24). Our testing with more recent models shows significant improvements for both harm and severity. If you would like to discuss an AI-assisted version of HCAT, contact us.
| Variant | Setting | Country | Year | Authors | Link |
|---|---|---|---|---|---|
| Persian localisation | Translation and expert Delphi validation | Iran | 2025 | Vafaee Najar et al. | Article |
| Learner-mistreatment reporting framework | Medical education | Canada | 2025 | Rachul et al. | Article |
| End-of-life care complaint analysis tool | NHS end-of-life care (licensed derivative) | England | 2024 | Walker & Dowling | Article |
| Japanese translation of the taxonomy | Five-year analysis at a Tokyo tertiary teaching hospital | Japan | 2024 | Uramatsu et al. | Article |
| HCAT (unmodified) | National validation across 16 public hospitals | Ireland | 2022 | O'Dowd et al. | Article |
| HCAT (unmodified) | Great Ormond Street specialist paediatric hospital | UK | 2022 | Wray, Williams & Oldham | Article |
| HCAT-DK | Danish translation — the first non-English edition | Denmark | 2021 | Morsø et al. | Article |
| HCAT(GP) | General practice; public training video | Ireland | 2021 | O'Dowd, Lydon & O'Connor | Article |
| HCAT (unmodified) | Reliability testing on patient compensation claims | Denmark | 2019 | Bogh et al. | Article |
| Out-of-hours GP modification | Out-of-hours general practice | Ireland | 2018 | Wallace et al. | Article |
| RSDM-PCT dental fork | Dental education | USA | 2017 | Fredericks-Younger et al. | Article |
| Compliments / praise extension | Complaints and praise at an Italian hospital | Italy | 2017 | Mattarozzi et al. | Article |
| Dutch regulatory variant | Healthcare inspectorate | Netherlands | 2016 | Bouwman et al. | Article |
| Focus | Setting | Country | Year | Authors | Link |
|---|---|---|---|---|---|
| AI | Validating large language models against HCAT harm coding | UK | 2025 | Bunt et al. | Article |
| Application | Maternity survey: dark figures of unreported problems | Denmark | 2025 | Clausen et al. | Article |
| Review | Scoping review: complaints and claims in quality improvement | International | 2025 | Hansen et al. | Article |
| AI | Primary care; LLMs tested against HCAT(GP) coders | Singapore | 2025 | Koh et al. | Article |
| Application | Stage-specific harm in a new hospital (coded in Korean) | South Korea | 2025 | Kwon et al. | Article |
| Application | Time-series analysis of complaints in new hospitals | South Korea | 2025 | Kwon et al. | Article |
| Application | Out-of-hours primary care compensation claims | Denmark | 2025 | Køpfli et al. | Article |
| Application | Physician narratives of complaints during residency | Canada | 2025 | McDougall et al. | Article |
| Commentary | Editorial: challenges and opportunities in learning from complaints | UK | 2025 | Reader | Article |
| Application | Shanghai hotline complaints with spatial analysis | China | 2025 | Wang et al. | Article |
| Commentary | Perspective: from complaint analysis to quality improvement | Denmark | 2024 | Birkeland, Bogh & Morsø | Article |
| Application | Online complaints about city hospitals during COVID-19 | Türkiye | 2024 | Çınar et al. | Article |
| Application | Nourishment problems at a hospital | Denmark | 2024 | Clausen et al. | Article |
| AI | Large language models drafting complaint replies | Singapore | 2024 | Yong et al. | Article |
| Application | Compliments about nursing and midwifery care | Australia | 2023 | Baker, White & Redley | Article |
| Application | Odense University Hospital: disproportionality analysis of 6,366 complaints | Denmark | 2023 | Bogh et al. | Article |
| Application | Laser treatment center, plastic surgery hospital | China | 2023 | Ding et al. | Article |
| AI | Online patient feedback as a safety valve (automated language analysis) | England | 2023 | Gillespie & Reader | Article |
| Application | Government complaint hotline | China | 2023 | Han et al. | Article |
| Application | Odense University Hospital: implementation, training and dashboard | Denmark | 2023 | Morsø et al. | Article |
| Application | Obstetric care complaints | Denmark | 2023 | Walløe et al. | Article |
| Application | College complaints against resident physicians | Canada | 2022 | Crosbie et al. | Article |
| Application | General hospital (Spanish-language) | Peru | 2022 | del Río-Mendoza et al. | Article |
| Application | Emergency-care compensation claims: hot spots and blind spots | Denmark | 2022 | Morsø et al. | Article |
| Application | HCAT(GP) applied to real general-practice complaints | Ireland | 2022 | O'Dowd et al. | Article |
| Application | Post-operative complaints in spine surgery | USA | 2022 | Ronald et al. | Article |
| Application | Nursing and midwifery complaints; HCAT in VHIMS | Australia | 2022 | Street, Russell & Considine | Article |
| Application | Integrating complaints and staff incident reports, London teaching hospital | UK | 2022 | Van Dael et al. | Article |
| Application | National complaints-handling policy case study | England | 2022 | van Dael et al. | Article |
| Application | Pandemic-era complaints at a medical center | Taiwan | 2022 | Wang et al. | Article |
| Application | Taxonomic review at Mayo Clinic hospitals | USA | 2021 | Elias et al. | Article |
| Application | Patient letters of compliment | England | 2021 | Gillespie & Reader | Article |
| Application | Neurosurgery: compliments and complaints | UK | 2021 | Jones et al. | Article |
| Application | Complaint severity predicts hospital mortality, 59 NHS trusts | UK | 2021 | Reader & Gillespie | Article |
| Application | Compensation claims after emergency-care reorganisation | Denmark | 2020 | Birkeland et al. | Article |
| Application | ENT departments at two teaching hospitals | UK | 2020 | Bujoreanu et al. | Article |
| Review | Systematic review of general-practice complaints | International | 2020 | O'Dowd et al. | Article |
| Review | Realist review: learning from complaints in healthcare | UK | 2020 | van Dael et al. | Article |
| Application | Linking complaints, incidents and adverse events (surgery) | Netherlands | 2019 | de Vos et al. | Article |
| Application | Metropolitan maternity service | Australia | 2019 | Nowotny et al. | Article |
| Application | Radiology complaints, nine-year series | Netherlands | 2019 | van den Berg et al. | Article |
| Application | Hot spots and blind spots, 56 NHS trusts (open data + R scripts) | England | 2018 | Gillespie & Reader | Article |
| Application | Intensive care vs general wards, academic medical center | Taiwan | 2018 | Jerng et al. | Article |
| Application | Image-guided interventional radiology | USA | 2018 | Salazar, Burk & Abujudeh | Article |
| Application | Outpatient cancer care (Dana-Farber) | USA | 2017 | Mack et al. | Article |
| Development | HCAT development and reliability testing | UK | 2016 | Gillespie & Reader | Article |
| Application | Serious complaints to the NSW healthcare commission | Australia | 2016 | Harrison et al. | Article |
| Development | Systematic review: 88,069 complaints, three-domain taxonomy | International | 2014 | Reader, Gillespie & Roberts | Article |