scatter plot, independent variable, dependent variable, discreet variable, continuous variable,  trend, line of best fit (trend line), outlier

Interactive Component Under Construction

• In an experiment to measure the temperature of water over a 5 minute interval, the time can be freely chosen.  The temperature of the water will not affect the heating time.  Heating time is independent of water temperature.

• In a 5 minute experiment, the water temperature increases as the heating time continues.   The water temperature is dependent on the amount of time it has been heated.

• Experiments depend on the logic, If "the independent variable changes", then, "dependent variable will increase/decrease/not change".

Continuous Variables

Variables that have continuous intervals that are unbroken sequences (e.g. growth of a plant) are represented by line graphs.

• Heating time and water temperature represent variables which are continuous and can be broken into smaller units (i.e. seconds and ^oC).   Connecting data points with a line illustrates the pattern that may have occurred between measurements.

Discrete Variables

Discrete variables have measurements that are distinct, periodic, and unconnected between data points (e.g. the distance an athlete throws a discus) and are represented by bar graphs.

• Student test scores are discrete and cannot be broken into smaller units.  Each student has an unique mark (bar).  There is nothing to connect the students together so a line between them is meaningless.

trend - relationship between two sets of data. The trend will show one of the 3 types of relationships between variables are:

• linear (straight line)
• non-linear (curved line or other pattern)
• no relationship at all

line of best fit (trend line) - A line on a scatter plot which can be drawn near the points to more clearly show the trend between two sets of data.

outlier - a point in a sample separated from the main body of the sample

Click the "Clear Points" button. Click on two points on the grid.  The points will be connected by a line.  See what happens if you click on other points on the line.

Click the "Clear Points" button. Click on two points on the grid.  The points will be connected by a line.  See what happens if you click on grid points that are not on the line. These are outliers.

• Click and drag data points to change their positons.
• The value of r is the correlation coefficent.  It ranges between -1 and 1.   It is part of the applet, but will not be emphasized in this lesson.

source:  http://ictcm.tamu.edu/Wisconsin_2001/Scatterplot/

• Click the "Load Data File" button to see the first scatterplot sample.   The other samples are available from the pulldown menu.  To display the sample, click the "Load Data File" button after selecting a sample.
  • Click on various spreadsheet cells and change the values.
  • Click "Enter"in either cell of the last row if you wish to add additional data.
  • Click on "Update Display" to plot the points.  Notice the effect the change has on the line of best fit.
• Create your own scatterplots by entering the data points into the spreadsheet to the left of the graph.
  • The correlation coefficent ranges between -1 and 1.  It is part of the applet, but will not be emphasized in this lesson.
  • The slope and intercept of the line of best fit is given, but will not be emphasized in this lesson.

source:  http://math.hws.edu/javamath/config_applets/index.html

There are many questions which could be asked about this relationship:

• Is the relationship linear (straight-line) or does the scatter represent nothing more than a random collection of points since there is no relationship??
• Does the value of y depend upon the value of x or vice versa?
• How strong is the relationship, do the points form a perfect line?

Olympic Gold Medal Winning High Jump (1900 - 1984)

source:  quizregsol.html

In this experiment:

• what are the dependent and independent variables?
• are the variables continuous or discrete?
• is the relationship between the dependent and independent variables linear or non-linear?
• what trend is illustrated?

source:  BIO 256 - Assignment 9

In this experiment:

• what are the dependent and independent variables?
• are the variables continuous or discrete?
• is the relationship between the dependent and independent variables linear or non-linear?
• what trend is illustrated?

Scatter Plot  of CEO Salaries

Description: The data are the age and annual salary(in $thousands) of the chief executive officer (including bonuses) for 60 small highly ranked firms.

Reference: Forbes, November 8, 1993, "America's Best Small Companies,". 

Webstat Directions: 

Look at all 3 steps before you start.  When you click on the button below, Webstat will open.