ECON 230
Lab 3
The goal of this lab is to understand and find simple probabilities and conditional
probabilities, and to use the Multiplication Rule and the Addition Rule.
Part 1: Create a table with your qualitative variable V1 and
quantitative variable V2.
(2 points)
For your Qualitative Variable, return to Lab 2 and choose the largest slice of the pie
graph to label the first column. Label the second column “others”.
For your Quantitative Variable, V2, label the first row LOW to indicate values that are
at “the median or lower.” Label the second row as HIGH to indicate values that are
“higher than the median.” You found the median in Lab 2.
For a student who has more Democratic candidates than Republican candidates, the
chart will look like:
Qualitative Variable, V1 (political party)
Quantitative
Variable, V2
(Year)
For the data in the chart, this student has 22 Democratic candidates, 9 of whom have
low values for year and 13 of whom have high values for year. This student has 18
candidates who are not Democrats, 10 of whom have low values for year and 8 of
whom have high values for year.
If there is a tie between Democrat and Republican for the most common category,
choose Democrat as your most common category.
Look at your data and count up the observations for each of the four cells in the table.
Place the sums in each cell and be sure that the numbers in all of the cells sum to 40.
Also record the sums for each row and each column.
Part 2: Find simple probabilities.
(1 point each)
A. Compute the probability of being in Row 1. (For example, P(low value for
year)).
B. Compute the probability of being in Column 1. (For example, P(Democrat)).
C. Compute the probability of being in Row 1 and Column 1 using the appropriate
frequency from your table. (For example, P(Democrat and low value for year)).
1
Democrat Others
Low 9 10
High 13 8
