Statistical Studies &
Sampling Methods

A gym randomly assigns members into two groups. Group A follows a new workout program; Group B continues their current routine. After 8 weeks, muscle gain is compared. What type of study is this?

A wildlife biologist watches and records how many deer visit a watering hole each day during summer. No interaction with the deer occurs. Which type of study is this?

A school randomly selects 100 students and asks them: "Would you support a longer lunch period?" Their responses are used to estimate the views of all 800 students. What type of study is this?

KIS assigns every student a unique ID. A random number generator picks student IDs until 60 students are selected for a survey. Every student has an equal chance of being chosen. What sampling method is this?

A hospital administrator randomly selects 8 hospitals from across the country, then surveys ALL nurses at each selected hospital. Which sampling method is used?

A school divides its 1,200 students into four grade levels (9th–12th). A random sample of 30 students is then drawn from EACH grade level. What sampling method is this?

A researcher lists all 500 employees by ID (001–500). She randomly picks #007 as a starting point, then selects every 10th person: 007, 017, 027… What is this method? 💡 Hint: The starting point is random, but the rest follow a FIXED rule. Don't confuse with Simple Random!

A city council member stands outside City Hall and surveys every person who walks by about a new parking law. Which sampling method does this represent?

A retailer places feedback cards at the front of the store. Customers may choose whether or not to fill them out. What sampling method is this?

A news website posts an online poll: "Do you agree that social media harms teenagers?" Anyone who visits can vote. Which type of bias is MOST present? 💡 Hint: Think about WHO chooses to respond and why they bother clicking.

A survey question reads: "Don't you agree that students deserve longer lunch breaks?" How does this wording introduce bias? ⚠ Focus on the language used in the question — not who is surveyed.

Which statement CORRECTLY distinguishes an experiment from an observational study?

In a drug trial: Group A receives the actual medication; Group B receives a placebo (sugar pill). Outcomes are compared after 8 weeks. Which group is the EXPERIMENTAL group and which is the CONTROL group?

The control group in an experiment is best described as:

Cluster sampling and Stratified sampling both divide the population into groups. What is the CRITICAL difference? ⚠ This is the most commonly confused pair in this entire unit!

Researchers observe 300 students over a semester, recording who eats breakfast and what test scores they receive — without changing any student's behavior. Students who eat breakfast tend to score higher. What is the MAIN limitation of this study?

A gym satisfaction survey is sent ONLY to members who visited the gym in the past week. Long-time members who rarely attend are completely excluded. Which concept does this BEST illustrate?

Which of the following sampling methods has the GREATEST risk of producing biased results? 💡 Recall the ☆ symbols marked in your notes next to specific methods!

Method 1: A pollster divides voters by region (Northeast, South, Midwest, West) and randomly selects voters from EACH region. Method 2: Every voter is assigned a number, and a random generator picks 1,000 of them. What are these two methods called?

A study finds that cities with MORE ice cream shops also have HIGHER crime rates. A reporter concludes: "Ice cream shops cause crime." What is the most accurate statistical critique of this conclusion? 💡 Hint: What type of study could produce this finding? Can it prove cause-and-effect?