ScatterPlots

Example of Scatter plot:


 * __Scatter plots__** show the relationship between two variables by displaying stat points on a two-dimensional graph.

Example of Scatter Plot Smoothing below:
 * Scatter plot Smoothing**
 * Scatter plots may be "smooth" by fitting best fit line to the data.
 * This line attempts to show the non-random component of association between the variables
 * Scatter plot Smoothing may be accomplished using:
 * A straight line (line of best fit)
 * A quadratic or polynomial line


 * Different Types of Relationships**:
 * __Positive Relationship__ (as shown below) would be indicated if the dots suggest a line going **up** from left to right, meaning as one variable increases, the other **increases** as well.


 * __Negative Relationship__ would be indicated if the dots suggest a line going **down** from left to right, meaning that as one variable increases, the other **decreases**.


 * No relationship** would be indicated if the scatter plot dots suggest a completely **horizontal line**, a completely **vertical line**, or **no line** at all (as shown below).



WHAT YOU NEED TO KNOW FOR THE SAT (according to CollegeBoard)
 * Students would be expected to identify the general characteristics of the line of best fit by looking at the scatterplot
 * Student **would not** be expected to use formal methods of finding equation of the line of best fit
 * Students will be expected to interpret data displayed in tables, charts, and graphs.

Example Problems:



(A) A (B) B (C) C (D) D (E) E (Correct answer is at the bottom of the page)
 * 1) A science class bought 20 different batteries of various brands and prices. They tested each battery's duration by seeing how long it would keep a motor running before losing power. For each battery, the class plotted the duration against the price, as shown above. Of the 5 labled points, which one corresponds to the battery that cost the least amount per hour of duration?

2. What is the percent increase in the net income from April to May?

(A) 1.5% (B) 105% (C) 150% (D) 1.8% (E)165% (Correct answer is at the bottom of the page)

3. In the following bar graph, the greatest change in the net income of Joe's Lemonade Stand occurred between between what two months?

(A) Feb-Mar (B) Apr-May (C) Jan-Feb (D) May-June (E) Mar-Apr (Correct answer is at the bottom of the page)

Answers to Questions:
 * C
 * C
 * A

Sources: [|Cliffnotes] [|NetMBA] [|CollegeBoard] [|SparkNotes]