Graphing 101

Draw and Identify the Axes

Remember DRY MIX R- Responding I- Independent Y- Y-axis X- X-axis D- Dependent M-Manipulated R- Responding I- Independent Y- Y-axis X- X-axis

The title should contain both the independent and dependent variables. Example: How Temperature Affects The Respiration Rate of Goldfish

Scale min and max numbers used on each axis. (Does not have to begin at zero). min and max numbers should be a little lower than lowest value and a little higher than the highest value Chose a scale that will utilize most of the graph paper This allows you to have a smaller range which emphasizes the comparisons/trends in the data.

The Best Scale Graph #1 The Y-axis scale is from 0-100 but the largest value is only 35. Graph #2 The Y-axis scale is now from 0-40. ---2nd Graph does a better job emphasizing the comparisons between coins.

Steps to Find Scale Find the range of the data for the Y Axis (67-32= 35) Count number of lines/boxes on axes (20) Divide the range number by the number of boxes (35÷20=1.75) round to 2 to make easier Each box will be worth 2 degrees Repeat for the X Axis (6÷20=0.33) Each box is worth less than a day, 3 box =1 day Each third line should be labeled with the day

Intervals The interval is the amount between one value and the next Look at your minimum and maximum values you set up for both the Y and X-axis. Use appropriate interval for the scale you have chosen. Highly recommended to use a common number for an interval such as 2, 5, 10, 25, 100, etc.

Intervals The interval for the Y-axis is 8 The X-axis does not have numerical data and does not need an interval.

Labels Both axes need labels so we know exactly what the independent and dependent variables are. The dependent variable must be specific and include the units used to measure the data (such as “number of drops”). DV label IV label

Labels DV label IV label

TAILS T.A.I.L.S. Scale Title Axis Another handy acronym to help you remember everything you need to create your graphs….. T.A.I.L.S. Title Axis Interval Labels Scale

Bar Graphs vs Line Graphs

Bar Graphs Bar graphs are descriptive. They compare groups of data such as amounts and categories. They help us make generalizations and see differences in the data.

Line Graphs Line graphs show a relationship between the two variables. They show how/if the IV affects the DV. Many times, the IV plotted on the X-axis is time. They are useful for showing trends in data and for making predictions. Can be used to compare multiple sets of data, using different lines within the same graph

Example

Multiple Sets of Data When graphing multiple data sets on the graph, use a distinctive color of pen, or style of line, for each data set. Place an example of the color or line style off to the side of the graph (Key) Label it with the name of the information being displayed. For example: Seedlings

Analyzing Data: Standard Deviation and Standard Error

Examine data points. Observe the pattern the data forms on the graph. From the pattern the data makes on the graph, determine the type of relationship between the x and y variables. Most times it will be best to use a smooth continuous line called a “best fit” line. Draw your best fit line so that it goes a little past your last data point.

A measure of how spread out the data is from the mean Standard Deviation: A measure of how spread out the data is from the mean Lower standard deviation: Data is closer to the mean Greater likelihood that the independent variable is causing the changes in the dependent variable Higher standard deviation: Data is more spread out from the mean More likely factors, other than the independent variable, are influencing the dependent variable

Actual data sets aren’t always so pretty...

Measure of accuracy, if the true mean is known Standard Error: Indication of how well the mean of a sample (x) estimates the true mean of a population (μ) Measure of accuracy, if the true mean is known How close a measured value is to the TRUE value Measure of precision, if true mean is not known How close a measured value is to other measured values

How do we use Standard Error? Create bar graph mean on Y-axis sample(s) on the X-axis chemical 1 mean = 30 cm chemical 2 mean = 50 cm

Add error bars! ± SE Indicate in figure caption that error bars represent standard error (SE)

Analyze! Look for overlap of error lines: If they overlap: The difference is not significant If they don’t overlap: The difference may be significant

  Which is a valid statement? Fish2Whale food caused the most fish growth Fish2Whale food caused more fish growth than did Budget Fude  

Statements: In all four regions, more males exhibited the trait measured than did females. More males in region 3 exhibited the measured trait than did females  