Lesson 8: Sampling and Inference

September 23, 2025

Review:

Presentation:

Census and Sampling
- Census = attempt to count entire population
  - US Census every 10 years
  - Most costly non-military federal government operation (except bailing out Wall Street)
- Sample = gather info from a portion of the population
  - Sample Types
    - Voluntary response sample
      - Complete an optional survey
      - Inherent bias
      - Example: Survey Monkey or Google Forms
    - Simple random sample
      - select from a population
      - each individual has equal chance of being selected
      - Example: random selection of subset of enrolled students
    - Stratified random sample
      - divide population into groups or strata
      - random sampling, equal chance of selection within each group
      - Example: random selection within major (30% CIS, 35% Mgmt, 35% Econ)
- Video: Census and Sampling

Activity:

Break into 4 groups.
Each group must design a 3-6 question survey on a topic interesting to classmates (e.g., favorite food, study habits, music preferences, commuting times, coffee vs. tea, campus activities).
Survey must include at least one categorical, one ordinal (ranking), and one numerical question (see examples below).
Keep it short so everyone can answer quickly.
Each group must submit your set of survey questions.

Example Survey:

Q1. Categorical
What is your preferred study environment?

Q2. Ordinal
How often do you review class notes after lecture?

Q3. Numeric
On average, how many hours do you study in a typical week?
____ hours

Q4. Categorical
Which type of device do you use most often for coursework?

Q5. Ordinal
How stressed do you feel about upcoming exams?
(1 = Not at all stressed, 5 = Extremely stressed)

Justin