prior probability: meaning, definition, pronunciation and examples
Low/Very LowTechnical/Academic
Quick answer
What does “prior probability” mean?
In Bayesian statistics, the probability assigned to a hypothesis before considering new evidence.
Audio
Pronunciation
Definition
Meaning and Definition
In Bayesian statistics, the probability assigned to a hypothesis before considering new evidence.
More broadly, any initial assumption about the likelihood of an event, based on pre-existing knowledge or established theory, used as a starting point for analysis.
Dialectal Variation
British vs American Usage
Differences
No lexical or conceptual differences. Purely a technical term.
Connotations
None beyond its technical definition.
Frequency
Equally rare and confined to technical contexts in both varieties.
Grammar
How to Use “prior probability” in a Sentence
The prior probability of [NOUN PHRASE] is [ADJECTIVE/NUMBER]We assign a [ADJECTIVE] prior probability to [HYPOTHESIS][HYPOTHESIS] has a prior probability of [NUMBER]Vocabulary
Collocations
Examples
Examples of “prior probability” in a Sentence
verb
British English
- [No standard verb form derived from this noun phrase]
American English
- [No standard verb form derived from this noun phrase]
adverb
British English
- [No standard adverb form derived from this noun phrase]
American English
- [No standard adverb form derived from this noun phrase]
adjective
British English
- The prior-probability assessment was crucial.
- They used a prior-probability distribution.
American English
- The prior probability assessment was crucial.
- They used a prior probability distribution.
Usage
Meaning in Context
Business
Virtually unused, except in highly technical risk analysis or quantitative finance roles.
Academic
Core term in statistics, data science, machine learning, philosophy of science, and experimental psychology.
Everyday
Extremely rare. Might be used humorously or metaphorically (e.g., 'The prior probability of him being on time is zero.').
Technical
The primary domain. Essential for Bayesian inference, spam filtering, medical diagnostic algorithms, and machine learning models.
Vocabulary
Synonyms of “prior probability”
Strong
Neutral
Weak
Vocabulary
Antonyms of “prior probability”
Watch out
Common Mistakes When Using “prior probability”
- Using it interchangeably with 'likelihood' (which is probability of data *given* a hypothesis).
- Pronouncing 'prior' as /ˈpriːɔːr/ instead of /ˈpraɪə/ or /ˈpraɪɚ/.
- Writing 'prior-probability' with a hyphen when used as a standalone noun phrase.
FAQ
Frequently Asked Questions
No. 'Probability' is a general concept. 'Prior probability' is a specific type of probability in Bayesian inference, representing a starting belief before new evidence is incorporated.
In a technical sense, it is a subjective starting point, not a factual claim to be 'right' or 'wrong'. However, a poorly chosen prior can lead to slower convergence or biased results if it strongly contradicts the true state of the world.
It is a cornerstone term in Bayesian statistics, machine learning (especially naive Bayes classifiers), probabilistic forecasting, and any field using formal Bayesian reasoning, such as parts of epidemiology, psychology, and economics.
The direct opposite is the 'posterior probability', which is the updated probability of the hypothesis *after* the new evidence has been considered and combined with the prior.
In Bayesian statistics, the probability assigned to a hypothesis before considering new evidence.
Prior probability is usually technical/academic in register.
Prior probability: in British English it is pronounced /ˌpraɪə ˌprɒbəˈbɪlɪti/, and in American English it is pronounced /ˌpraɪɚ ˌprɑːbəˈbɪləti/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “[None specific to this term]”
Learning
Memory Aids
Mnemonic
Think of 'prior' as 'before'. PRIOR PROBABILITY is the PROBABILITY you have BEFORE you see the new data.
Conceptual Metaphor
A STARTING POINT on a map of belief; a BASELINE or FOUNDATIONAL assumption that gets refined.
Practice
Quiz
What is the primary function of a 'prior probability' in Bayesian analysis?