{"entity":{"id":"linear-probe","kind":"term","name":"Linear probe","aka":["linear probe","linear probing","linear evaluation","linear head on frozen features","frozen embedding to linear head"],"tldr":"A linear probe is a simple linear model (logistic or ridge regression) trained on a frozen model's embeddings to test how much useful information those embeddings hold.","summary":"Logistic regression models the log-odds of an outcome as a linear combination of inputs (Wikipedia); trained on frozen embeddings it becomes a probe of the representation, since whatever it can predict must be linearly readable from the features. Pathology foundation-model papers report linear-probe accuracy across many tasks as their headline comparison, and frozen embedding, then PCA to a few hundred dimensions, then a linear head is the standard extraction recipe for transcriptome models too.","asOf":"2026-09-24","wikipedia":"https://en.wikipedia.org/wiki/Logistic_regression","links":[{"label":"Wikipedia","url":"https://en.wikipedia.org/wiki/Logistic_regression"}],"tags":["cansim-terms"],"related":["cancer-ai-vocabulary"],"cancers":[],"sections":[],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["fine-tuning-vs-frozen","embedding","logistic-regression-term","ridge-regression"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":["Listed in the CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme; CanSim page path /terms/linear-probe."],"provenance":{"editedBy":"OnCo CanSim terms wave (Wikipedia summaries, standards and project pages, GDC and FDA pages, Europe PMC)","editedOn":"2026-09-24","note":"CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme"},"category":"Methods and models"},"route":"/terms/linear-probe/","neighbours":{"term":[{"id":"cancer-ai-vocabulary","kind":"term","name":"Cancer AI vocabulary (CanSim terms map)","route":"/terms/cancer-ai-vocabulary/"},{"id":"embedding","kind":"term","name":"Embedding (learned representation)","route":"/terms/embedding/"},{"id":"fine-tuning-vs-frozen","kind":"term","name":"Fine-tuning versus frozen features, and LoRA","route":"/terms/fine-tuning-vs-frozen/"},{"id":"logistic-regression-term","kind":"term","name":"Logistic regression and nearest-centroid classifiers","route":"/terms/logistic-regression-term/"},{"id":"ridge-regression","kind":"term","name":"Ridge regression and the multilayer perceptron","route":"/terms/ridge-regression/"}]}}