Locked vs. Adaptive Algorithm
Distinction between models whose behavior is fixed at release vs. those that continue learning.
Definition
A locked algorithm produces the same output for the same input every time after release. An adaptive algorithm changes its behavior over time as it is exposed to new data, either continuously or in scheduled retraining cycles. Most authorized AI devices are locked: they may be updated, but each update is a planned, validated release. Truly adaptive, continuously learning devices raise questions about how to verify performance, so regulators expect strong controls. In the US, a PCCP lets manufacturers pre-specify the changes an algorithm can undergo, and the EU AI Act requires substantial changes to high-risk systems to go through a new conformity assessment unless predetermined.What this means in practice
FDA's PCCP framework lets manufacturers prospectively define and validate the boundaries of allowable adaptive changes so retraining does not require a new submission for each model update.Examples
- A diagnostic AI that learns to identify new patterns in medical images as it processes more patient scans is an adaptive algorithm requiring a PCCP.
- An insulin pump algorithm that adjusts dosing recommendations based on a patient's continuously acquired glucose data and activity levels is an adaptive algorithm.
- A risk stratification tool that uses a fixed set of patient demographics and historical health records to predict disease likelihood is a locked algorithm.
- •Failing to establish clear performance bounds and risk mitigations for adaptive algorithm changes can lead to regulatory non-compliance.
- •Treating an adaptive algorithm as a locked algorithm for validation purposes will result in insufficient oversight of its evolving behavior.
- •Not documenting the data used for training and retraining, along with corresponding version control, can create significant auditability issues.
- •Assuming all adaptive algorithm changes are minor and do not impact safety or effectiveness can lead to patient harm and regulatory scrutiny.
Frequently asked questions
Cross-references
Related terms
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Guiding principles for the development of AI/ML-enabled medical devices.
FDA mechanism to pre-authorize specific modifications to AI/ML-enabled devices.
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· Same categoryAAMI Technical Information Report providing guidance on applying Agile software development practices within an IEC 62304-compliant medical device software lifecycle.
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The detailed procedural section of a PCCP that specifies how planned modifications to an AI/ML model will be developed, validated, and implemented.
Systematic differences in model performance across demographic or clinical subgroups.
Where this term appears across MedTech Terms.
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Sources
3 sourcesEvery citation below opens the original document. Each is graded against our source-tier hierarchy so you can see what rests on binding law versus commentary.
- 1MDCG Software GuidanceTier 2 VerifiedMDCGhealth.ec.europa.eu
- 2FDA - Software as a Medical Device (SaMD)Tier 2 VerifiedFDAfda.gov
- 3FDA - AI/ML-Enabled Medical DevicesTier 2 VerifiedFDAfda.gov
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