Module 4 (Contingency Tables, Bar Graphs, Histograms, Box Plots, Scatter and Line Plots) Flashcards
What is a contingency table?
A contingency table summarizes the frequency (or proportion) of sampling units in each level of a categorical variable.
- A table showing allergy symptoms (e.g., asthma, eczema) in rural vs. urban settings.
What is the difference between one-way and two-way contingency tables?
One-way: Summarizes one categorical variable.
Two-way: Summarizes two categorical variables.
- Example: A two-way table showing allergy types and whether people live in rural or urban settings.
What are marginal and conditional distributions?
Marginal distribution: Shows the total counts or proportions for each row/column in a table.
Conditional distribution: Shows the relative frequencies of one variable within levels of another variable.
When should you use a bar graph
Bar graphs are used to visualize categorical data, either for one or two variables.
- A bar graph showing the number of jobs in renewable energy categories like wind, solar, and hydro.
What’s the difference between grouped and stacked bar graphs?
Grouped bar graphs: Display levels of the second variable adjacent to each other.
Stacked bar graphs: Stack levels of the second variable on top of each other within each group.
- Example: A grouped bar graph showing beverage choices by night and morning people.
When should you use a box plot?
Use a box plot when you want to display the spread of a numerical variable across groups.
- A box plot showing egg production across Canadian provinces.
What are the key elements of a box plot?
Box plots show the minimum, 1st quartile, median, 3rd quartile, and maximum. The interquartile range (IQR) is the height of the box, and whiskers extend to data points within 1.5 times the IQR.
When is a grouped box plot used?
Grouped box plots are used when you have two categorical variables and one numerical variable to display how the numerical variable changes across the categories.
- A grouped box plot comparing energy production in Canada vs. the U.S. from different sources.
When should you use a scatter plot?
Scatter plots are used to show the relationship between two numerical variables measured from the same sampling unit.
What is the difference between the axes in experimental and observational studies in scatter plots?
Experimental: The x-axis is the independent variable (manipulated), and the y-axis is the dependent variable (response).
Observational: Both variables are covariates since neither is controlled by the researcher.
When should you use a line plot?
Line plots are used when data are collected repeatedly from the same sampling unit, showing changes over time or conditions.
- A line plot showing heart rate changes during and after exercise for two participants.
When should you use a histogram?
Histograms are used to visualize numerical data by dividing it into equal-sized bins and showing the frequency of data within each bin.
- A histogram showing the distribution of renewable energy production across U.S. states.
How do you decide on the number of bins for a histogram?
Choose the number of bins carefully—too few bins lose detail, and too many bins make patterns harder to see. Adjust bins to show clear patterns in the data.
- In energy data, too few bins might oversimplify, while too many bins may obscure key trends.
What is the key difference between histograms and bar graphs?
Histograms: Used for numerical data, with no gaps between bars.
Bar Graphs: Used for categorical data, with gaps between bars.
Example: Use a bar graph for categorical data like job sectors and a histogram for numerical data like energy production.
