Reflection: Connection to Prior Knowledge Describing Scatterplots  Section 4: Closing Discussion and Assignment
The applied nature of statistics makes it an excellent content area to expand students’ knowledge of graphs and equations. I find that my students have had a fairly good introduction to writing equations of lines in Algebra 1. Even if they are rusty today, after a skill refresher they can usually calculate slope and either use slopeintercept or pointslope formulas to write an equation of a line. They may not, however, have had such a solid foundation of the meaning of these graphs. Now, after having studied many other function types and numerous application models all year, is a good time to remind them that:

Ordered pairs always have the form (independent variable, dependent variable), commonly (x, y), and in the case of applications are packed with information about two things in relation to one another.

The yintercept is the resulting output when the input is zero. In many applications, this is the ‘starting value’ or at least a value that supplies important information.

The xintercept is the value required to give an output of zero. It is just as important as the yintercept.

The slope and the rate of change are the same thing. The rate is always “change of dependent variable” compared to “change of independent variable.” In an application, the rate can be described in the same units as the variables (eg. miles/hour for a graph showing distance in miles on the vertical axis and time in hours on the horizontal).
 Changing a fractional slope to a decimal is the same as converting a regular rate to a unit rate. In other words, if m=⅗ we could say that’s a rate of 3 miles per every 5 hours or a rate of 0.6 miles per hour.
Describing Scatterplots
Lesson 3 of 4
Objective: SWBAT describe the direction, form and strength of a relationship between two quantitative variables.
Big Idea: The appearance of a scatter plot can tell us a lot about the relationship between the variables on the axes.
Opening Activity
As a warmup, I ask my students to complete Review of Bivariate Data Displays, a worksheet that contains a summary of the previous day's discussion. They work independently to fill in the blanks in this worksheet, testing their recall of the previous day's lesson.
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Foldable Notes
We have spent some time discussing the various types of two variable data sets that we might come across (2 categorical, 2 quantitative, or one of each) and how to display each type. At this point, we focus in on data sets that can be displayed with a scatter plot.
I want my students to remember that the most important features of a scatter plot are Direction, Outliers, Form and Strength. To help them remember this, I use the mnemonic DOFS:
 D = the direction of the association between the two variables (positive or negative)
 O = whether or not there are outliers in the data set
 F = the form of the association (linear or curved)
 S = a measure of strength, or how close the dots are to the line or curve
In this lesson, we make a Foldable Resource for their notes that details best practices for describing these four characteristics of a bivariate data set.
For the next activity, I ask students to work in the pairs established in the previous day's lesson to practice describing scatterplots. Using their foldable notes and the Data Display Cards they sorted yesterday, my students will practice verbally describing the scatter plots to their partner. As they do this, I circulate around the room listening to the discussions and making notes about their progress [MP3].
I do not yet ask students to write down formal descriptions of these scatter plots because we have not yet discussed residuals and correlation coefficients. In order to do a thorough job of describing the scatter plots they will need to use these concepts, so I do not want them to get used to writing descriptions that omit them.
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When students have had 20 minutes to practice describing the data sets, I ask for volunteers to describe the scatter plots as I display them with a projector. I ask the class to critique their description and provide feedback.
The homework for this evening will be a "throwback" assignment, WS Writing Equation of a Line. In this assignment, students are asked to write the equation of a line given various starting information. This should be a pretty relaxing assignment because students spent a lot of time on linear functions in Algebra 1. In the next lesson, we will use regression equations to make predictions so I want students to be familiar with how the equation of a line is determined.
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