# Design of Studies (Pt. 1)

Homer White, Georgetown College

### In Part 1:

Always remember to make sure the necessary packages are loaded:

require(mosaic)
require(tigerstats)


## Observational Studies

### Relationship Questions

Really interesting questions in science are about relationships between variables:

• Usually one variable $$X$$ is considered explanatory
• The other variable $$Y$$ is considered a response

The explanatory variable might

• help explain
• help predict
• maybe even cause

the response variable.

### Relationship Question

Does smoking cause lung cancer?

• Explanatory $$X$$ is smoke (Yes, No)
• Response variable $$Y$$ is lung cancer (Yes,No)

### Relationship Questions

Learn about the attitudes data frame:

data(attitudes)
View(attitudes)
help(attitudes)


### Relationship Questions

Who gives the longest sentences on average: math/science majors, humanities majors, social science majors, or pre-professional majors?

• Explanatory variable $$X$$ = major
• Response variable $$Y$$ = sentence

### Quick Look (Numerical)

favstats(sentence~major,data=attitudes)

      .group  mean median
1 humanities 25.26     20
2   math.sci 30.49     30
3   pre.prof 25.02     25
4 social.sci 25.49     25


### Observational Study

Definition:

In an observational study researchers simply observe or question the subjects. In particular, they measure the values of the explanatory variable $$X$$ and measure the values of the response variable $$Y$$, for each subject.

## Causation

### Causation Questions

One of the most common reasons to study the relationship between two variables is to see if one of them causes the other.

### Speeding Causes Tickets

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could not find function "openplotmat"