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Chapter 3

PSYC 210 Chapter Notes - Chapter 3: Exploratory Data Analysis, Bar Chart, Central Tendency


Department
Psychology
Course Code
PSYC 210
Professor
Russell Day
Chapter
3

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Chapter 3
Displaying Data
A collection of numbers has to be interpretable, they first must be organized in
some sort of logical order
3e.1. Plotting Data
One of the simplest methods for reorganizing data is to make them more
intelligible is to plot them in some sort of graphical form
Data can be represented graphically in several common ways
Some of these methods are frequency distributions, histograms and stem-and-leaf
displays
Frequency Distributions
As a first step we can make a frequency distribution = a distribution in which
the values of the DV are tabled or plotted against their frequency of occurrence
Frequency distribution of the data is a way of organizing them in some sort of
logical order
For example of reaction times, we would count the number of times that each
possible reaction time occurred
3.2. Stem-and-leaf displays
A frequency distribution tells you how many times each value occurs and the
associated graph gives you a visual representation of the data
A very nice way of retaining both the individual values and the frequency of those
values is by creating a stem-and-leaf display = graphical display presenting
original data arranged into a histogram
Exploratory data analysis (EDA) = a set of techniques developed by John
Tukey for presenting data in visually meaningful ways
One of the simplest methods is the stem-and-leaf display
Leading digits = sometimes called the most significant digits are the leftmost
digits of a number (the tens)
These leading digits form the stem = vertical axis of display containing the
leading digits
Trailing digits = sometimes called the less significant are the digits to the right of
the leading digits
Leaves = horizontal axis of display containing the trailing digits
Raw data Stem Leaf
0,1,1,2,2,3,4,4,4,5,5 0 01122344 …
10,11,11,12,17,16 1 01123333 …
oFirst row shows that there are 2 ones, 2 twos, etc.
oSecond row shows that there are 2 elevens, 1 twelve etc.
From the stem-and-leaf display you could completely regenerate the raw data that
went into the display
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