# Graphs Displaying Data. Graphing Graphs are visual displays of data. Different types of graphs are used for different purposes. The correct type of graph.

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Graphs Displaying Data

Graphing Graphs are visual displays of data. Different types of graphs are used for different purposes. The correct type of graph must be used for the data collected. In other words, the data determines the graph type…you don’t choose the type you want!

Discrete or Continuous? When deciding on the type of graph to make, ask yourself: Is my independent variable discrete or continuous? Discrete variables are categorical e.g.: gender, brand of fertilizer, type of sandwich Use a BAR GRAPH with these variables Continuous variables are associated with measurements involving a standard scale with equal intervals e.g. amount of fertilizer in grams, time in seconds Use a LINE GRAPH with these variables

Graph Types Line graph Shows relationship between two variables Used to help show the trend, or pattern, in data Trends allow for predictions Independent variable goes on horizontal axis (x) Dependent variable goes on vertical axis (y) Bar graphs Display data that is not continuous Used to show comparisons between different sets of data or categories Pie Chart Uses circle sections to show parts of a whole

Making a Line Graph Will be used in most of our experiments Must have title, labeled axes, & units Must have reasonable spacing Line must take up graph space Line shouldn’t be to right or left of graph space Line shouldn’t be to top or bottom of graph space Line should be fairly centered, so make axis numbers fit your data Line should extend through (0,0) point when appropriate Line should NOT extend through (0,0) point when NOT appropriate

Line Graph Example What is this a graph of? How do you know? N.Y. Temperatures Title

Line Graph from Data Time is continuous. There are other time measurements possible between the measurements recorded. The experimenter could have recorded the temperature every hour, every half hour, or every minute. Therefore, a line graph is appropriate.

Best-Fit Line Graph best fit line graph – see p. 18 Connects with best smooth & continuous line Doesn’t necessarily go through all data points gets average.

Best-Fit Line Graph All show trend All allow for prediction Straight-line fitSmooth curve fit

Bar Graph A Bar Graph is appropriate here because the data shows lunch choices. Each choice is a separate category

Bar Graph Categories are the horizontal axis. Measurements are on the vertical axis. Each category has a separate bar.

Pie Chart (Circle Graph) A Pie Chart would be appropriate here to see what percent of students choose each type of exercise

Pie Chart (Circle Graph) 1 student of 8 chose swimming: 1/8 =.125 (x 100 = 12.5%) (1/8 of the circle) 2 students out of 8 chose jogging: 2/8 x 100 = 25% (1/4 of the circle) 4 students out of 8 chose soccer: 4/8 x 100 = 50% (1/2 of the circle)

Slope of a Line Slope is determined using the formula: Two points are selected on the line. The coordinates of those points are taken. Two points: (2, 3) and (4, 9) point 1 coordinates and point 2 coordinates so: (2, 3) and (4, 9) 9-3 = 6 = 3 4-2 2 The slope of this line is 3. X 1, Y 1 X 2, Y 2

Slope of a Line What is the slope of this line? Let’s call R point 1 and S point two. R coordinates: (1, 6) S coordinates: (4, 12) Slope = X 1, Y 1 X 2, Y 2 12 - 6 = 6 = 2 4 - 1 3

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