Invited talk at the XVIII International Workshop on Maximum Entropy and Bayesian Methods (Maxent98), Garching / München (Germany), July 27-31 1998. physics/9811046

For a postscript version of the article, click here.

Piazzale Aldo Moro 2, I-00185 Roma (Italy)

Email: dagostini@roma1.infn.it

URL: http://www-zeus.roma1.infn.it/~agostini/

**Abstract.**
The intuitive reasoning of physicists in conditions of uncertainty
is closer to the Bayesian approach than to the frequentist
ideas taught at University and which are considered the
reference framework for handling statistical problems. The combination
of intuition and conventional statistics allows practitioners
to get results which are very close, both in meaning and in numerical
value, to those obtainable by Bayesian methods, at least in simple
routine applications. There are, however, cases in which
``arbitrary'' probability inversions produce unacceptable or
misleading results and in these cases
the conscious application of Bayesian reasoning
becomes crucial. Starting from these considerations, I will finally
comment on the often debated question:
``is there any chance that all physicists will become Bayesian?''

**Key words:** Subjective Bayesian Theory, High Energy Physics,
Measurement Uncertainty

**Table of Contents**

- INTRODUCTION
- MEASUREMENT UNCERTAINTY
- PROFESSED FREQUENTISM VERSUS PRACTICED SUBJECTIVISM
- HEP physicists ``are frequentist''
- HEP physicists ``are Bayesian''
- Intuitive application of Bayes' theorem
- Bayes versus Monte Carlo
- EXPLICIT USE OF BAYESIAN METHODS IN HEP
- EXAMPLES OF MISLEADING RESULTS INDUCED BY CONVENTIONAL STATISTICS
- CONCLUSIONS
- REFERENCES