# Class 04: An Introduction to R, Continued

Back to An Introduction to Linux and R. On to Topic 4: Random Sampling.

This outline is also available in PDF.

Held: Wednesday, 30 January 2008

Summary: We continue our explorations of the R environment for statistics.

Notes:

• Can we design a study that will help us predict which stairwell will be open?
• I may ask questions as a way of taking attendance.
• Cassie is setting up office hours Sunday, Tuesday, and Thursday evenings. We're still working on where.

Overview:

• Detour: Comments on Topic 3.
• Short review.
• Lab, continued.
• Reflection.

## Quick Review of Topic 3

Some questions for you:

• What is a population?
• What is a sample?
• If we care about populations, why do we often look at samples, rather than complete populations?
• What is a parameter?
• What is a statistic?
• What makes a sample representative?
• What makes a process for generating samples biased?
• What is an observational study?
• What are some difficulties of observational studies?
• What are the alternatives to observational studies?

Some questions to ask when you read studies (cribbed from p. 43)

• To what population can you reasonably generalize the results of the study?
• Can you reasonably draw a cause-and-effect connection between the explanatory variable and the response variable?

Observation:

• Most statisticians believe you cannot draw cause-and-effect connections in observational studies.
• A surprising number of economists believe that you can design observational studies that produce cause-and-effect conclusions.

## R, Continued

• Quick review
• Four key data types: Numbers, strings, vectors, frames
• Can do computations
• Can build graphs
• Can build misleading graphs (example of barplot from data that needs to be tabulated)
• Lab!
• Reflection

Back to An Introduction to Linux and R. On to Topic 4: Random Sampling.

Disclaimer: I usually create these pages on the fly, which means that I rarely proofread them and they may contain bad grammar and incorrect details. It also means that I tend to update them regularly (see the history for more details). Feel free to contact me with any suggestions for changes.

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Samuel A. Rebelsky, rebelsky@grinnell.edu

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