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## GRAPHING RULES

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**GRAPHING RULES**• The purposes of creating graphs are to: • Display data in a different format • Make it easier for you to see patterns, trends and relationships. • While are there are several types of graphs, the types of graphs we will focus on this year will be: • bar graphs • line graphs • line plots (sometimes called pictographs)**Bar Graphs**• Normally used to compare categorical, ordered, or discrete variables. These changes are NOT continuous. • Categorical variables—described by a word label, not a number (e.g. different brands of paper towels or types of animals at the zoo) • Ordered variable-these are categorical variables that can be put in order (e.g. cool, warm, hot) • Discrete variables- describe by whole numbers only (e.g. 1, 2, 3 teaspoons) • Bar graphs are useful to get an overall idea of trends in responses • Often used to display data for polls and surveys**When is it best to choose to draw a bar graph?**• When you are comparing the total number of things (such as data from surveys, polls or discrete measurements)**That’s right…it had no title or labels on axes**Weight (lbs) Type of Trash**Double (or triple) Bar Graph**• Double (or triple) bar graphs are also used to show and compare total number of things, but each group of data is divided into two (or three) • Because you are comparing more than one group of data, you should have a key.**Line Graphs**• Often used to show a change over a period of time When is it best to choose to draw a line graph? • Show the relationships between the independent and dependent variables (how the DV responds to the IV)**Single or multiple line graphs**• use a single line when you are showing only one variable level • Multiple (two, three, four, etc.) line graphs are also used to show the relationship between the variables, but each independent variable level is shown. • Because you are comparing more than one group of data, you should have a key.**Single line graph**• The independent variable in graph A is ____________________ • The dependent variable in graph A is ____________________**Multiple line graph**• The independent variable in graph B is ____________________ • The dependent variable in graph B is ____________________ • The different levels/groups in graph B are _________________ and ____________________ • 4. How did you figure out the groups? • ____________________**shows the frequency of data along a horizontal number line**(x-axis) plots data on a number line with a symbol (x) above the numbers The number of x's above each number/amount indicates how many times each number/amount occurred. Note: There is no y-axis for this type of graph Original source: http://ellerbruch.nmu.edu/classes/cs255w03/cs255students/nsovey/p5/p5.html (modified by J. Solari on 10/12) Line Plots- for what are they used?**When is it best to use a line plot?**It is best to use a line plot (instead of a bar graph) when you want to show the frequency (how often something occurs).**How to read a line plot**• Line plots allow several features of the data to become more obvious. For example, outliers, clusters, and gaps are apparent. • Outliersare data points whose values are significantly larger or smaller than other values • Clusters are isolated groups of points • Gapsare large spaces between points Ages of people who live in the apartment building Original source: http://ellerbruch.nmu.edu/cs255/jnord/lineplot.html, modified by J. Solari 10/12/10**How to create a line plot**• Once data is collected it is then time to make a line plot. • 1. Determine the scale to be used. If the data is best described in 100's have the scale increase by hundreds, if all the data can fit on a scale 0-10 then make it 0-10. • 2. Next draw a horizontal line across the paper (x-axis). • 3. Break the line into EQUAL parts that will hold your scale. • 4. List the data. Place an X over the correct number for each of the datum collected. If a number is repeated then place the X above the other. • 5. Label the x-axis and give it an appropriate title**Graphing Rules**• Use a bar graph when making comparison of data and a line graph to show continuous change over time. 1. Draw the axes • Use the entire graph paper to set up x- and y-axes. Margins below x-axis and next to y-axis should be no larger than one inch (about 2.5 cm). • Be Neat.Use a ruler to draw margins. 2. Identify the variables a. The x-axis is horizontal axis and the y-axis is the vertical axis. • The x-axis represents the independent variable • The y-axis represents the dependent variable**Graphing Rules, continued**3. Determine a Scale for Each Axis Your goal in determining a scale for the axes is to fit the entire range of data over the available space on the graph paper. To select an appropriate scale, you need to: • Determine the variable range (max-min) for each axis. • Count the number of (blue) lines along the x and y axes. Each line represents an interval. • Divide the # of Intervals by the range (I/R) and round down to nearest number.**Graphing Rules, continued**4. Number and Label each Axis • Mark the scale values on each axis • Label each axis with the type of data and unit**5. Plot the data points and Draw the Graph**• On a line graph: 1) plot each pair of data values (dependent-independent pair) on the graph with a dot 2) draw a curve or line that best fits the data points (using a ruler). 3) you may have multiple sets of dependent-independent data. If so, use a different color to plot each set of data pairs. • On a bar graph: make all bars the same width, evenly space out the bars (not touching). If you are creating a multiple bar graph, the sets of data which belong to each category on x-axis can touch the bars in the same set. color or shade the bars differently for each category on x-axis**6. Include a Key, if necessary**• Place in upper right or left hand corner of graph; use when graphing two or more sets of data (multiple bar or line graph) to identify all of the groups or variable levels. • Use different colored pencils to represent the different groups or variable levels.**Title your graph**It should clearly describe the information (data/experimental results). Place title at top-center of graph. (“The Effect of IV on DV” or IV vs. DV)