1. Topic 3: Data Basics

2. First Bag
Second Bag
Third Bag

3. Observations, variables, and data matrices

4. Data Matrix
Example of data that might be collected from a first-day survey of students:
Variable
Student
Gender
Class Yr. …
Study Time 1 M SO 2 60 3 F 8 4 . 42 5
Case
Observation

5. Types of variables All variables Quantitative Categorical Continuous
Observations are numerical values that represent different magnitudes
Categorical
Observations belong to a set of distinct categories
Continuous
Possible values form an interval like [0, 10]
Discrete
Possible values form a set of separate numbers like 1, 2, 3, …
Regular
Categorical
Categories have no natural ordering
Ordinal
Categories have a natural ordering

6. Examples of variables gender – categorical, regular
sleep - numerical, continuous
bedtime - categorical, ordinal
countries - numerical, discrete
dread - categorical, ordinal

7. independent variables

8. Association between variables
Does there appear to be an association between a possum’s head length and skull width?
skull width (mm)
head length (mm)

9. Relationships among variables
Does there appear to be a relationship between hours of study per week and GPA?

10. Independent Variables
If there is little to no evidence that two variables are associated, then they are said to be independent.