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Lecture 2

PSYC 241 Lecture Notes - Lecture 2: Percentile Rank, Frequency Distribution, Level Of MeasurementPremium

3 pages15 viewsSpring 2017

Department
Psychology
Course Code
PSYC 241
Professor
Kristen Leighton
Lecture
2

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Lesson 2: Frequency Distribution
We can describe any data set with three pieces of information
Shape of the distribution
Central tendency
Variability
Distributions tell us:
Every possible score
Actual scores
Frequency distribution
Show how many people are located in each category on the scale of measurement
Present an organized picture of the entire set of scores
Show where each person is located relative to others
Frequency Distribution Tables
X column
Categories on the scale measurement
Values are listed from the highest to lowest (without skipping any)
Frequency column
Tallies for each value (how often each X value occurs in the data set)
Frequencies for each X value
The sum of the frequencies should equal N
The 'x' column contains every possible score
The 'f' column indicates the frequency of each score
Grouped Frequency Distribution
When a frequency distribution table lists all of the individual categories (X values) it is
called a regular frequency distribution
This works well if we have very few scores
For many values (like exam scores), a grouped frequency distribution is used
The X column lists groups of scores, called class intervals, rather than individual values
Guidelines
~10 class intervals
Width should be simple number (2, 5, 10, 20, etc.)
Bottom score should be a multiple of the width
All intervals should be the width with no gaps or overlaps
Frequency distribution graphs
One alternative to tables is to create visual representations of the data
This allows us to more easily see the shape of a distribution
The score categories (X value) are listed on the X axis
The frequencies are listed on the Y axis
Scores from interval scale --> histogram or polygon
Histograms
Bar is centered above each score (or class interval)
Height of the bar corresponds to the frequency
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