Ch. 2
Skewed
line contains a "tail"
Relative Frequency
the fraction or percent of the time that an event occurs in an experiment
Symmetry
Left and Right are identical
Identify the different modalities.
Unimodal- 1 hump Bimodal- 2 humps (do not need to be of equal size) Multimodal- 3+ humps (do not need to be of equal size)
Cumulative Relative Frequency
percentage at or below Ex. 2, 5, 9 -> 0.10, 0.25, 0.45
Percentile Rank
percentage of measurements in the distribution below that score value
P%
percentile rank
If the tail of a line is pointing to the right, it is ____ skewed.
positively
Score Value (Given Percentile Rank) Formula
score value = LRL + [(P% x n)/100) -nb]/nw x I
x
scores
I
size of the class Interval - 2, 3, 5, or multiple of 5 - Upper Real Limit - Lower Real Limit
N
sum of all frequencies
Where can n be found?
top of cumulative frequency column or sum of frequency
n
total Number of measurements in the distribution
Score value
value for which you are determining the percentile rank
What does the x-axis indicate?
variable measured
What orientation is the y-axis?
vertical
Central Tendency
what score value represents the center of the distribution
Percentile
when a score is identified by its percentile rank
How do you indicate the sum of all frequencies?
Σ = N =
When working on a Grouped Frequency Distribution Table, always work from ____ to _____.
bottom/top
Where can nb be found?
cumulative frequency column, below x
Variability
degree to which measurements in a distribution differ from one another
Grouped Frequency Distribution Table
each row in the table is a "group" of possible score values rather than a single score
Frequency Distribution Components
- Scores - Meaning - Frequency - Relative Frequency - Cumulative Frequency - Cumulative Relative Frequency
Cumulative Frequency
- the sum of the frequencies for that score and all previous scores - should equal N at top
Score Value (Given Percentile Rank) Process
- use (P5 x n)/100 to find which class interval contains the score at this percentile - once interval is identified, use frequency and cumulative frequency to complete the formula and find the score value
Identify the 2 different types of variability.
1.) Clustered 2.) Spread
What are the 2 types of frequency distribution graphs?
1.) Histograms 2.) Polygons
What are the 3 characteristics of frequency distribution graphs?
1.) Shape 2.) Central Tendency 3.) Variability
Rules for Creating a Grouped Frequency Distribution Table
1.) table should include 8-10 rows (anymore or less would not create clear change on a graph) 2.) class interval range of scores should be 2, 3, 5, or multiple of 5 3.) lowest value of the lowest class interval should be easily divisible by interval size
Percentile Rank (Given a Raw Score) Formula
P% = { [ ( score value - LRL ) / I x nw] + nb} / n x 100
Do not round a score value if it is ____.
continuous
How many steps are in the Percentile Rank (Given a Raw Score) Process?
1
What are the 3 characteristics of shapes on a graph?
1.) Symmetry 2.) Skewed 3.) Modality
Which frequency distribution graph is a bar graph?
Histogram
LRL
Lower Real Limit of the class interval containing the score value
nb
Number of measurements Below the class interval containing the score value
nw
Number of measurements Within the class interval containing the score value
Which frequency distribution graph is a line graph?
Polygon
Which frequency distribution graph is more common?
Polygon because it is easier to see the shape
Cumulative Frequency Formula
age the value to the previous sum Ex. 2, 3, 4 -> 2, 5, 9
Meaning
explain the significance of the scores and/or their category
f
frequency
Where can nw be found?
frequency column
What does the y-axis indicate?
frequency or relative frequency
Relative Frequency Formula
frequency/sum of all frequencies f/N
Class interval
group of possible score values
What orientation is the x-axis?
horizontal
Modality
how many "humps" in a line
Frequency
how many times a certain score occurs within the collected data
Interval size
i
Identify the interval in the range 0-4
i = 5
If we have a group frequency distribution, label x-axis with ____.
midpoint of class intervals (rather than full interval to reduce stretching)
If the tail of a line is pointing to the left, it is ____ skewed.
negatively