Unit 2 Intro: Central Tendency

Unit 2: Getting Started with Central Tendency

After this module, you will be able to…
Explain measures of central tendency
Define & compute the Mean, Median and Mode
using a calculator
using Excel's Toolpak
Define, recognize, and give examples of variables with each level (scale) of measurement:
nominal
ordinal
interval
ratio
Identify the appropriate use of mean, median, mode
Use the Data Analysis Toolpak to compute descriptive statistics
Identify measures of central tendency in research based reports.

Review for this unit
Population
Sample
Variables
A dimension that varies across individuals
Can take on more than one value
Values / attributes
One of the possible values of a variable

Overview of central tendency
Central tendency
A statistical measure
A single score to define the center of a set of scores
Purpose
Find the single score that is most typical or best represents the entire group
Estimate a population
The central tendency (average) of a sample is sometimes used to estimate the entire population

Three kinds of average
Mode – most common value in the data
Median – middle case (data point) in the data
Mean – balance point of all the data
The type of average used must match the characteristics of the variable.

Level (Scale) of Measurement
Variables are measured with different scales
The measure of central tendency should match the type of values
Four levels will bedefined in the lecture
Nominal
Ordinal
Interval
Ratio

Summation notation
Most of the techniques in statistics involve adding up a set of numbers
The capital Greek letter sigma (Σ) indicates that the items following it should be added up
A single letter, often X, can stand for all the data for a single variable
Σ X means “add all the data for the variable X”

Preview of the Data Analysis Toolpak
Chapter 2 shows how to generate a full suite of Descriptive Statistics with the Data Analysis Toolpak (p. 57-61)
The Toolpak is a number-cruncher but presents them in a plain way.
Salkind begins to show you how to make the numbers more presentable, a topic which we take up in Units 3 and 4.

Unit 2: Getting Started with Central Tendency