# StatTutor: Driving experience and monthly auto premium (Question 2)

Description of activity and Excel instructions: StatTutor Driving experience and monthly auto premium (Question 2)

Dataset: Direct link for auto_premium.xls not available.

## Contents

## Exploratory data analysis

- Rename "Sheet 1" to "Q1".
- Rename "Sheet 2" to "Q2".
- Copy and paste the raw data from sheet "Q1" to sheet "Q2".

### Create a scatterplot

In preparation for creating the scatterplot,

- Rearrange or delete columns of data so that the data for the two variables to be plotted are adjacent to one another.
- Sort the data so that observations with missing values can be easily avoided when specifying the data for inclusion in the scatterplot.

Use the *Chart Wizard* to create a scatterplot.

- Select the columns containing the two variables to be plotted.
- Select
**Insert**>**Chart...**.

The *Chart Wizard* displays.

In *1. Chart Type*:

- Select
**XY (Scatter)**. - Select the
**Points Only**version.

In *2. Data Range*:

- Click '
*Data series in columns*. - Check
**First row as label**.

No changes are needed for *3. Data Series*.

In *4. Chart Elements*:

- Enter a title for the chart.
- Enter a title for the X axis (explanatory variable).
- Enter a title for the Y axis (response variable).
- Decide if you want to display a grid in the chart background.
- Uncheck the
*Display Legend*box.

Calc creates a scatterplot.

- Check that the scales for the x and y axes are reasonable given the data. Adjust as needed.

If you want to change the shape or size of the data points:

- Double click on the graph to enter edit mode
- Right click on the data points
- Select
**Object Properties...** - Explore the options in the
*Icon*section, in the*Line*tab.

### Create a correlation coefficient

Use a formula to compute the correlation:

- Click in a cell outside of the first two columns of data.
- Type "=CORREL([range1],[range2])" where [range1] is the first column of data and [range2] is the second column of data.

Return to the StatTutor exercise for Question 2 to provide a comparison of the data in the two groups: describe the key features of the data display and support your description with numerical measures. (Be sure to include the numerical results in your description.)

## Calculate p-value

Calc does not include a formula or data analysis routine to calculate the "t-test for the slope" of a regression line. You can use Excel for this activity, or the web-based p-value calculator for the correlation coefficients at danielsoper.com. (Although note that the online stats calculator returns a slightly higher, although still very small, p-value than the value reported by Excel.)

Return to the StatTutor exercise for Question 2 to report results and draw conclusions.