Unit 4: Describing Data: Distribution Flashcards
Frequency Distributions
How many people (or objects, animals, items) were similar on the variable
that they have the same score or are in the same category
Can be used for qualitative (categorical) and quantitative data
Simple vs. Grouped:
A grouped frequency distribution includes class intervals in
which data are grouped together.
* A grouped frequency distribution is used rather than listing out
individual data.v
- Conventions of a grouped frequency distribution:
The groups must have equal ranges.
A particular score or observation can fit into only one group.
What is displayed on a frequency distribution table:
Frequency (raw count)
Relative Frequency (proportion or percent)
Cumulative Frequency Distributions
Sum of the group and all groups below (or above) it in a frequency
distribution
graphs for Categorical Variables
Pie chart
Bar graphs
graphs for Continuous Variables
- Histograms
- Boxplots
Categorical Variables
The distribution lists the categories/ or groups and gives the count or percent of individuals who fall into each category.
a diagram consisting of rectangles whose
area is proportional to the frequency of a variable and whose
width is equal to the class interval
Histograms
drawing a histogram
For large datasets and/or quantitative variables that take many
values:
▪ Divide the possible values into bins (e.g., classes, intervals) of equal
widths.
▪ Count how many observations fall into each interval.
▪ Draw a picture representing the distribution―each bar height is equal
to the number (percent) of observations in its interval
Distributional Shape
“Normal” or “Skewed”?
* Unimodal or Multimodal?
The Normal Distribution
Bell-shaped curve
* Perfectly normal
* Symmetrical
* Tails never touch the horizontal axis
* Unimodal
Skewed Distribution
Not symmetrical
* Positively skewed
* Skewed to the right
Skewed Distribution
Negatively skewed
* Skewed to the left
Unimodal
- 1 peak: data congregate around one key location
