Lesson 1.2: Sampling and Experiments
Lesson Learning Objectives
- Distinguish between population parameters and sample statistics.
- Understand that observational studies can suggest associations but cannot demonstrate causal relationships.
- Discuss the key features of various sampling schemes, including: simple random, stratified random, cluster, systematic, multistage, and convenience samples.
- Understand the distinction between sampling variability and bias.
- Discuss the potential sources of bias in sample surveys.
- Distinguish between experiments and observational studies.
- Understand the principles of control, randomization, replication, and blocking in experimental design.
- Discuss the difference between a completely randomized design and a randomized block design.
- Discuss the role of blinding, placebos, and control groups in experimental design.
- Understand the meaning of the term “statistically significant.”
Lesson 1.2 Checklist
| Learning activity | Graded? | Estimated time |
|---|---|---|
| Read OpenIntro Statistics sections 1.3 and 1.4 and supplementary notes | No | 45 mins |
| Watch instructional videos | No | 15 mins |
| Answer two lesson check-in questions | Yes | 15 mins |
| Work on practice exercises | No | 2 hours |
| Explore suggested websites | No | 15 mins |
Learning Activities
Readings 📖 and Instructional Videos 🎦
Sampling
Read Section 1.3: Sampling Principles and Strategies in OpenIntro Statistics (Diez et al., 2019) CC BY-SA 3.0. Analytic research typically begins with a clear study question and a consideration of the subjects/cases and variables to measure to answer that question. This section introduces you to data collection, sampling principles, and strategies used to achieve research goals.
As you read, look up new terminology in the Glossary and self-assess your understanding by attempting the guided practice exercises.
Watch the video, Data Collection Principles (Barr & Diez, 2013), on data collection and sampling (duration 00:03:09):
Watch the video, Observational Studies and Sampling Strategies (Barr & Diez, 2015-b), to learn about sampling (duration 00:03:13):
Experiments
Read Section 1.4: Experiments (Diez et al., 2019) CC BY-SA 3.0. An experiment (or experimental study) is a study in which researchers investigate the possibility of a causal connection between variables by controlling the values of the explanatory variable(s) for selected cases. Experiments must be designed carefully to ensure conclusions can be drawn from the results and this section describes ideas for doing this.
After reading this section, watch the following video, Designing Experiments (Barr & Diez, 2015-a), on basic principles of experimental design (duration 00:03:09):
Sample Surveys, Observational Studies, and Experiments
Read Supplementary Notes 1.2, which provides a little more in-depth coverage of these topics.
Lesson Check-in Questions ✍
Virtual Statistical Software Lab 💻
There is no virtual statistical software lab for Lesson 1.2.
Virtual Statistical Software Lab Questions ✍
Practice Exercises 🖊
Work on the following exercises in OpenIntro Statistics: Exercises 1.13, 1.15, 1.17, 1.19, 1.21, 1.23, 1.25, 1.27, 1.29, 1.31, and 1.33 and Chapter Exercises 1.35, 1.37, 1.39, and 1.41 (Diez et al., 2019) CC BY-SA 3.0. Check your answers using these solutions (Diez et al., 2019) CC BY-SA 3.0. You’ll deepen your understanding much more effectively if you genuinely attempt the questions by yourself before checking the solutions.
Work on the practice questions in the WeBWorK platform, which are linked from your Moodle course. Check your answers using the solutions provided.
Suggested Websites 🌎
- Statistics Canada (2021) has a great online training tool, Statistics: Power from Data! It includes a comprehensive discussion on Sampling.
- Simple Learning Pro (n.d.) has a series of introductory statistics videos on YouTube, including the following videos on experiments and sampling:
- Causation vs Association, and an Introduction to Experiments [Video] (2015-a) (duration 00:07:05)
- Placebo Effect, Control Groups, and the Double Blind Experiment [Video] (2015-c) (duration 00:03:35)
- Types of Experimental Design [Video] (2015-d) (duration 00:06:36)
- Types of Sampling Methods [Video] (2015-e) (duration 00:04:49)
- Census, Nonresponse, and Undercoverage [Video] (2015-b) (duration 00:01:52)
Media Attributions
Bodycare, Clinic, Clipboard, Doc, Doctor, Female, by Ilmicrofono Oggiono (2015), on Flickr, CC BY-SA 2.0
References
Barr, C. D., & Diez, D. [OpenIntroOrg]. (2013, May 5). Data collection principles [Video]. YouTube. https://youtu.be/2N_bkiyTiXU
Barr, C. D., & Diez, D. [OpenIntroOrg]. (2015-a, May 5). Designing experiments [Video]. YouTube. https://youtu.be/g7JGe_ykB3I
Barr, C. D., & Diez, D. [OpenIntroOrg]. (2015-b, Aug. 30). Observational studies and sampling strategies [Video]. YouTube. https://youtu.be/KyuaX10l3GQ
Diez, D. M., Çetinkaya-Rundel, M., Barr, C. D. (2019). OpenIntro Statistics (4th ed.). OpenIntro. https://www.openintro.org/book/os/
Ilmicrofono Oggiono. (2015). Bodycare, clinic, clipboard, doc, doctor, female [Photograph]. Flickr. https://flic.kr/p/qu4nVM
Simple Learning Pro. (2015-a, Nov. 23). Causation vs association, and an introduction to experiments (3.1) [Video]. YouTube. https://www.youtube.com/watch?v=kKHx9T6XUI0
Simple Learning Pro. (2015-b, Nov. 25). Census, nonresponse, and undercoverage (4.2) [Video]. YouTube. https://www.youtube.com/watch?v=EZrP_av3cmA
Simple Learning Pro. (2015-c, Nov. 25). Placebo effect, control groups, and the double blind experiment (3.2) [Video]. YouTube. https://www.youtube.com/watch?v=GMqrOdCx4Yg
Simple Learning Pro. (2015-d, Nov. 25). Types of experimental designs (3.3) [Video]. YouTube. https://www.youtube.com/watch?v=10ikXret7Lk
Simple Learning Pro. (2015-e, Nov. 25). Types of sampling methods (4.1) [Video]. YouTube. https://www.youtube.com/watch?v=pTuj57uXWlk
Statistics Canada. (2021, Sep. 2). Statistics: Power from data! [Catalogue no. 12-004-x]. https://www150.statcan.gc.ca/n1/edu/power-pouvoir/toc-tdm/5214718-eng.htm
