Stats Review: Descriptive Statistics Flashcards
Frequency Distribution Tables
Help organize values so you can see patterns and detect outlier values
What are the two types of outlier values and how do you remove them?
- Mistakes: Simply remove data value from stats
- Extremes: Keep the data value but use as a limitation of the study (causing scew).
Grouped Frequency Table
Combine nearby items into score “bins” that represent a range of values.
What is an example of a variable that can be grouped?
Age- different decades
What are the three characteristics that bins (groupings) have to have?
- Exclusive
- Equal sized
- Exhaustive
Exclusive
Each item fits in no more than one bin (minimum and max values).
Equal sized
Each bin has the same range
Exhaustive
Every item in the data fits into a bin.
Raw Frequency Table
Reflects the sample size
What is a limitation or raw frequency tables?
It can be hard to compare across studies with different sample sizes.
Relative Frequency Tables
Express the frequency in proportions or percentages.
What is the formula to find the proportion of a bin?
Proportion of a bin = Frequency of the bin / Total of all frequencies
Cumulative Frequency
Counts accumulated scores across bins
What are cumulative frequency graphs useful for?
Counting scores below or above a threshold value
When is cumulative frequency possible?
Only is the levels have an order to them (age ranges)
How can cumulative frequency also be counted?
In relative proportions or percentages
% Total
The percentage of observations out of the total number
Cumulative Percent
Relative to the total number of observations that have data
Histograms
A graphical depiction of a frequency table by plotting how often different values occur.
What are the 4 expectations of histograms
- X values have possible values
- Bins should be equal sized, exclusive, no gaps, and exhaustive of all possible scores.
- Y axis is the frequency
- The increment of values on the y axis should be equal sized
What are histograms used for?
To describe the shape of a variable’s distribution.
What do areas with higher frequencies represent?
There are more values that fall within that given region.
What are the 3 types of distribution shapes?
- Normal
- Skewed
- Bi-modal
Normal Distribution
A symmetrical distribution of data with a single peak and a bell shape.
Skewed Distribution
Many observations clumped on one end, with a “tail” of extreme values on the other (skewed) end.
Where is the tail end of a negative skew?
Towards the more negative values
Where is the tail end of a positive scew?
Towards the more positive values.
Bi-Modal Distribution
Graphs that have two peaks.
