# Lesson 2: Summarizing Data

This is an online version of a printed textbook. It is not intended to be an online course.

Refer to the book or to the electronic PDF version (511 pages) for printable versions of text, figures, and tables.

## Overview

Imagine that you work in a county health department and are faced with two challenges. First, a case of hepatitis B is reported to the health department. The patient, a 40-year-old man, denies having either of the two common risk factors for the disease: he has never used injection drugs and has been in a monogamous relationship with his wife for twelve years. However, he remembers going to the dentist for some bridge work approximately three months earlier. Hepatitis B has occasionally been transmitted between dentist and patients, particularly before dentists routinely wore gloves.

**Question**: What proportion of other persons with new onset of hepatitis B reported recent exposure to the same dentist, or to any dentist during their likely period of exposure?

Then, in the following week, the health department receives 61 death certificates. A new employee in the Vital Statistics office wonders how many death certificates the health department usually receives each week.

**Question**: What is the average number of death certificates the health department receives each week? By how much does this number vary? What is the range over the past year?

If you were given the appropriate raw data, would you be able to answer these two questions confidently? The materials in this lesson will allow you do so — and more.

## Objectives

After studying this lesson and answering the questions in the exercises, you will be able to:

- Construct a frequency distribution
- Calculate and interpret four measures of central location: mode, median, arithmetic mean, and geometric mean
- Apply the most appropriate measure of central location for a frequency distribution
- Apply and interpret four measures of spread: range, interquartile range, standard deviation, and confidence interval (for mean)

## Major Sections

- Section 1: Organizing Data
- Section 2: Types of Variables
- Section 3: Frequency Distributions
- Section 4: Properties of Frequency Distributions
- Section 5: Methods for Summarizing Data
- Section 6: Measures of Central Location
- Section 7: Measures of Spread
- Section 8: Choosing the Right Measure of Central Location and Spread
- Summary and References
- Exercise Answers
- Self-Assessment Quiz
- Answers to Self-Assessment Quiz