Study Design Lab

The goal of this lab is to practice working with the various sampling methods covered in the lecture for today. In addition, we need to begin getting comfortable defining population/sample/parameter/statistic for the situations we encounter. (We will add more to this lab on Friday)

Question 1 (Conceptual)

• Part A: What is a census, what are the pros and cons of conducting one?
• Part B: What is a sampling frame?
• Part C: What does it mean for a sample to be representative?
• Part D: What do we need to be true of a sample in order to generalize results to a population?

Question 2 – Gallup Polls

The Gallup Poll (known for conducting many different types of public opinion surveys) uses a procedure called random digit dialing, which creates phone numbers based on a list of all area codes in America in conjunction with the associated number of residential households in each area code.

Part A: Give a possible reason the Gallup Poll chooses to use random digit dialing instead of picking phone numbers from the phone book.

Part B: What types of biases can arise when conducting a phone-based poll survey?

Question 3 – Evaluating Sampling Methods

A university wants to determine what fraction of its undergraduate student body support a new $25 annual fee to improve the student union. For each proposed method below, indicate whether the method is reasonable or not. Explain why or why not for each.

1. Survey a simple random sample of 500 students.
2. Stratify students by their field of study, then sample 10% of students from each stratum.
3. Cluster students by their ages (e.g., 18 years old in one cluster, 19 years old in one cluster, etc.), then randomly sample three clusters and survey all students in those clusters.

Question 4 – Defiining Things

For the previous example (university survey). Define the following:

• Population:
• Sample:
• Statistic:
• Parameter:

Question 5 – Course Satisfaction

A large chemistry class (at an unspecified university) has 160 students. All 160 students attend the lectures together, but the students are divided into 4 groups, each of 40 students, for lab sections administered by different teaching assistants. The chemistry professor wants to conduct a survey about how satisfied the students are with the course, and he believes that the lab section a student is in might affect the student’s overall satisfaction with the course.

Getting data and analyzing responses from all 160 students would be too difficult and time-consuming. Suggest a sampling strategy for carrying out this study. Explain why you would use this strategy and any benefits / drawbacks.

Question 6 – Cat Videos

Suppose you want to estimate the percentage of videos on YouTube that are cat videos. It is impossible for you to watch all videos on YouTube so you use a random video picker to select 1000 videos for you. You find that 2% of these videos are cat videos.

Part A: Determine which of the following is an observation, a variable, a sample statistic, or a population parameter

• Percentage of all videos on YouTube that are cat videos.
• 2%
• A video in your sample
• whether a video is a cat video

Part B: If instead of using a random video picker, we just looked at the first 1000 videos that show up for you on YouTube, what could go wrong? Explain.