2. Association Between Two Variables
Lesson
Group discussion
For each of the following pairs of variables, discuss the strength and direction of the correlation (if any):
- The floor space of an office and the number of desks that can fit
- The number of students on an excursion and the number of teachers supervising
- The number of text messages sent and the amount of prepaid credit remaining
- The distance driven by a car and the amount of fuel in the tank
- The height of a person and the number of hats they own
- A household electricity bill and the total income of the residents
- The amount of internet data and the age of the internet user
The average prices of an airline ticket on a particular route from the years 2001 to 2009 are shown in the table below:
| Average airline ticket prices (2001 to 2009) | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Year | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 |
| Price | \$280 | $180 | $270 | $260 | $240 | $190 | $230 | $220 | $190 |
Display this data in a scatterplot using a spreadsheet tool. Then fit a trendline to the data and display the equation of the line.
Group discussion
- Is this trendline accurate? Give reasons for your answer and comment on any factors that might be affecting the data.
The next table includes the prices from 2010 to 2014:
| Average airline ticket prices (2010 to 2014) | |||||
|---|---|---|---|---|---|
| Year | 2010 | 2011 | 2012 | 2013 | 2014 |
| Price | \$180 | $170 | $160 | $155 | $150 |
Plot this data on a separate graph, and display the equation of the trendline.
Group discussion
- How does this trendline compare to the one above?
- Use the equation of each line to predict the average price of an airline ticket in the year 2015. What do you see?