# Digital Health Metrics > A reference book of digital health metric definitions: what each metric means, how to calculate it, a worked example, data sources and caveats, and common pitfalls, organised for people building, running, and evaluating digital health products and services. Every topic is one metric or concept: definition, why it matters, how it is calculated, a worked example, data sources and caveats, pitfalls, and sources. The book has 31 topics in 53 locales; the links below are the en-gb edition. The same topic in another locale is at `//topics//` with that locale's own slug (see llms.json for the locale list). Machine translations are AI-assisted and pending review by a fluent speaker; en-gb is the reference text. ## Patient engagement and access - [Patient portal adoption rate](https://digital-health-metrics.github.io/en-gb/topics/patient-portal-adoption-rate/): registration, activation, and active use; three different rates too often conflated as one - [Telehealth visit rate](https://digital-health-metrics.github.io/en-gb/topics/telehealth-visit-rate/): the share of care delivered remotely, and why video and telephone should never be reported as one number - [Appointment no-show rate](https://digital-health-metrics.github.io/en-gb/topics/appointment-no-show-rate/): the oldest operational metric in healthcare, and one of the best-evidenced targets for digital reminders - [Patient engagement consistency rate](https://digital-health-metrics.github.io/en-gb/topics/patient-engagement-consistency-rate/): how regularly a patient interacts with a digital tool over time, as distinct from whether they have used it at all - [User retention rate](https://digital-health-metrics.github.io/en-gb/topics/user-retention-rate/): the cohort retention curve that separates a product with a sustainable use pattern from one riding a wave of novelty - [DAU/MAU stickiness ratio](https://digital-health-metrics.github.io/en-gb/topics/dau-mau-stickiness-ratio/): the standard product-analytics measure of engagement intensity across a whole user base - [Patient Net Promoter Score](https://digital-health-metrics.github.io/en-gb/topics/patient-net-promoter-score/): the widely used, and widely criticized, single-question satisfaction metric - [System Usability Scale score](https://digital-health-metrics.github.io/en-gb/topics/system-usability-scale-score/): a standardised 10-item questionnaire quantifying how usable a piece of software actually is ## Digital care operations and safety - [Clinical alert override rate](https://digital-health-metrics.github.io/en-gb/topics/clinical-alert-override-rate/): the standard signal for alert fatigue in clinical decision support - [Digital referral turnaround time](https://digital-health-metrics.github.io/en-gb/topics/digital-referral-turnaround-time/): the process metric that shows whether an e-referral system is actually saving time - [Time to intervention](https://digital-health-metrics.github.io/en-gb/topics/time-to-intervention-rate/): how quickly a clinical team responds to an automated health alert - [Bed-day reduction](https://digital-health-metrics.github.io/en-gb/topics/bed-day-reduction/): inpatient bed days saved by shifting recovery to a virtual ward, always reported alongside a safety metric ## Clinical outcomes and quality - [Biometric improvement rate](https://digital-health-metrics.github.io/en-gb/topics/biometric-improvement-rate/): the share of patients achieving a clinically meaningful change in a tracked biometric such as HbA1c or BMI - [Biometric stabilization rate](https://digital-health-metrics.github.io/en-gb/topics/biometric-stabilization-rate/): sustained control within a target range, as distinct from a one-off improvement - [Triage routing accuracy](https://digital-health-metrics.github.io/en-gb/topics/triage-routing-accuracy/): whether an AI or digital triage tool correctly routes a patient to the right level of care - [Medication adherence rate](https://digital-health-metrics.github.io/en-gb/topics/medication-adherence-rate/): the proportion of days a patient had access to their medication as prescribed - [Hospital readmission rate](https://digital-health-metrics.github.io/en-gb/topics/hospital-readmission-rate/): the metric most directly tied to payer economics and value-based care contracts - [ePROM completion rate](https://digital-health-metrics.github.io/en-gb/topics/epro-completion-rate/): the completion rate for electronic patient-reported outcome measures, and why a declining rate can itself be a clinical signal ## Marketing and growth economics - [True customer acquisition cost](https://digital-health-metrics.github.io/en-gb/topics/true-customer-acquisition-cost/): the fully loaded cost of acquiring one new patient, commonly undercounted by 30-50% - [LTV to CAC ratio](https://digital-health-metrics.github.io/en-gb/topics/ltv-to-cac-ratio/): lifetime value against true acquisition cost; 3:1 is the widely cited sustainable baseline - [Marketing efficiency ratio](https://digital-health-metrics.github.io/en-gb/topics/marketing-efficiency-ratio/): total revenue over total marketing spend, an independent check against platform-reported ROAS ## Digital health equity - [Digital access rate](https://digital-health-metrics.github.io/en-gb/topics/digital-access-rate/): the precondition metric for every other digital health measure in this book - [Digital literacy rate](https://digital-health-metrics.github.io/en-gb/topics/digital-literacy-rate/): whether patients who do have access can actually use it unaided ## Technical and operational infrastructure - [Physician burnout rate](https://digital-health-metrics.github.io/en-gb/topics/physician-burnout-rate/): tracked alongside clinician-facing digital tool burden, since badly designed software is a documented contributor - [Device uptime rate](https://digital-health-metrics.github.io/en-gb/topics/device-uptime-rate/): the foundational infrastructure metric underneath every remote monitoring programme ## Financial and economic value - [Cost per episode of care](https://digital-health-metrics.github.io/en-gb/topics/cost-per-episode-of-care/): the standard unit of financial comparison in value-based care contracts - [Emergency department diversion rate](https://digital-health-metrics.github.io/en-gb/topics/ed-diversion-rate/): patient contacts safely redirected away from the ED, always reported alongside a missed-emergency safety metric - [Return on investment (ROI) and value on investment (VOI)](https://digital-health-metrics.github.io/en-gb/topics/roi-and-voi/): whether a digital investment paid for itself financially, and whether it was worth doing accounting for everything that matters ## Evaluation frameworks - [RE-AIM framework](https://digital-health-metrics.github.io/en-gb/topics/re-aim-framework/): Reach, Effectiveness, Adoption, Implementation, and Maintenance; five dimensions rather than one metric - [WHO Digital Health Assessment Framework](https://digital-health-metrics.github.io/en-gb/topics/who-digital-health-assessment-framework/): WHO's guidance for assessing feasibility, safety, and equity across national-scale deployments - [ISO/TS 82304-2](https://digital-health-metrics.github.io/en-gb/topics/iso-ts-82304-2/): the international technical specification behind most health and wellness app quality labels ## Optional - [All topics A to Z](https://digital-health-metrics.github.io/en-gb/topics/) - [Contents in reading order](https://digital-health-metrics.github.io/en-gb/contents/) - [About](https://digital-health-metrics.github.io/about/) - [Source repository](https://github.com/digital-health-metrics/digital-health-metrics) - [Structured index (llms.json)](https://digital-health-metrics.github.io/llms.json)