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3. Maximum likelihood estimation

Aims | Objectives | Reading | Handouts & Problem Sheets | Questions | Links

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Aims

In this section we introduce the concepts of the likelihood function and the maximum likelihood estimate. For a distribution in a given parametric family, the likelihood function acts as a summary of all the information about the unknown parameter contained in the observations. Many important and powerful statistical procedures have the likelihood function as their starting point. Here we focus on method of maximum likelihood estimation, which could be said to provide the most plausible estimate of the unknown parameter for the given data.

Objectives

The following objectives will help you to assess how well you have mastered the relevant material. By the end of this section you should be able to:

  • Write down the general form of the likelihood function and the log-likelihood function, based on a simple random sample from a distribution in a general parametric family.
  • Define the maximum likelihood estimate(s) for one or more unknown parameters, based on a simple random sample from a distribution in a general parametric family.
  • Write down the general form of the likelihood equations(s), based on a simple random sample from a distribution in a general parametric family, and understand how and when the maximum likelihood estimate(s) can be obtained from the solution of the likelihood equations(s).
  • Find the explicit form of the likelihood equation(s) for a simple one- or two-parameter family of distributions, and solve to find the maximum likelihood estimate(s) of the unknown parameter(s).
  • Find the maximum likelihood estimate directly from the likelihood function for a simple one-parameter range family.
  • Compute the maximum likelihood estimate for population quantities which are simple functions of the unknown parameter(s). Examples of such functions include the population mean, the population median and the population variance, or appropriate poulation probabilities.

Suggested Reading

RiceChapter 8 Section 8.5 The method of maximum likelihood


Handouts and Problem Sheets

Copies of Handouts, Problem Sheets and Solution Sheets for the unit will be made available each week here.

Handout for Section 3 | Problem sheet 4 | Solution sheet 4

Copyright notice

© University of Bristol 2011

All material in these pages is copyright of the University unless explicitly stated otherwise. It is provided exclusively for educational purposes at the University and is to be downloaded or copied for your private study only, and not for distribution to anyone else.

Please also note that material from previous years' delivery of this unit is not necessarily a reliable indicator of what will be covered or examined this year.


Questions - set this week

PROBLEM SHEET 4 -- Questions 2, 4, 6


Interesting links

R demos (1) and (2) - the functions I used in lectures 6 and 7 to visualise sampling from a population and the value of parametric assumptions, and likelihood functions, respectively.

Chance
The Chance web site aims to awaken interest and motivate the study of statistics by making students more informed, critical readers of current news stories that use probability and statistics. Particularly interesting is the Chance News, the site's monthly newsletter, which provides relevant abstracts of articles from current newspapers and journals.

University of Georgia.
The applet below, which is part of a University of Georgia web site on population dynamics, enables you to visualize similar features for the maximum likelihood estimation of the parameter for a Binomial distribution.

Note that I have no control over the content or availability of these external web pages. The links may be slow to load, or may sometimes fail altogether - please email me to report if a link goes down. Similarly applets may be slow to load or run, but beware that you may experience problems if you try to exit them before they have finished loading.

Professor Peter Green, School of Mathematics, University of Bristol, Bristol, BS8 1TW, UK.
Email link Telephone: +44 (0)117 928 7967; Fax: +44 (0)117 928 7999
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