Guidelines for building a bar graph in Excel and using it in a laboratory report IB Biology (December 2012)

This guide begins with the building of the graph itself (it assumes basic calculations have been finished) For information about how to do basic calculations (mean, standard deviation, and standard error) see my video in Edmodo labeled “Mean Standard Deviation and Standard Error” ▫*NOTE* Also basic information about how to add error bars and perform t-tests can be seen in the posted videos “bargrapherrorbars” and “calculatingt_testsinexcel” respectively.

Checklist Before submitting graphs with a lab make sure you include the following (each is discussed in this guide): ▫1) Include two bar graphs of the data you are comparing (one with standard deviation error bars, the second with standard deviation) ▫2) Each graph should have a box below it with the number of the graph, type of error bars used, and the sample sizes of the bars. ▫3) Your t-tests should be used to both confirm and deny statistical significance.

4. (right click chart) 5.

6. Click on and remove any series already here Use the group name with independent variable level 9. Average for the group Click on red arrow and then the excel cell

10. (right click a number on the vertical axis) 12. (Fix the minimum of the axis at 0) 11.

13. Make sure you have the graph clicked on and go to “chart tools” at the top for these options to appear.

14. Make sure you have the graph clicked on and go to “chart tools” at the top for these options to appear.

15. Make sure you have the graph clicked on and go to “chart tools” at the top for these options to appear.

Group labels should include: 1) Exactly how you manipulated the independent variable 2) What the manipulation was supposed to accomplish Pointers on Graph Labels The horizontal label doesn’t have to be specific if you have the detailed labels to the right. Your title should include : 1) Exactly where the data is coming from 2) What that data is supposed to represent. Vertical axis label should include UNITS in almost all cases

Now the basic graph is completed! Next you need to add the error bars. ▫You need one graph for each type (standard deviation and standard error) ▫So make it easy on yourself and just right click and copy your graph and paste a copy next to it.

Checklist Item 1 Include two bar graphs of the data you are comparing: The one with standard deviation error bars allows you to discuss the variation in the data points recorded for each bar (in the conclusion). The second with standard deviation allows you to talk about the relative accuracy of each mean (mean indicated by a bar on the graph) and an initial idea of where there could be statistical significance.

Adding Error Bars

1. Select the bar you want to add an error bar to

5. 6.

Next Repeat steps 1-6 for each bar to add error bars with standard deviation (NOTE: Make sure you are selecting a different standard deviation for each. Each groups standard deviation should be different) THEN repeat the steps with the second graph to add error bars using standard error (NOTE: the only difference in the procedure is that each group’s standard error will be selected instead of standard deviation.)

Putting graphs into your report

Checklist Item 2 Each graph should have a box below it with: The number of the graph (they are numbered by the order they appear) Type of error bars used (standard deviation or standard error) Sample sizes of the bars ( shown as n = ____, if there are different amounts of data points for each bar this should be stated. Ex: n=11 (.5g NaCl), n=23 (1 g NaCl).

1. Go to insert (not shown) 2.

Numbering them by their order makes for easy referencing in conclusion. Source of error bars is stated. Sample size is stated. The correct format for a graph label.

Checklist Item 3 T-tests should be used to both: Confirm statistical significance (bars that don’t overlap are actually different, supported if p<.05) Deny statistical significance (bars that are close or overlapping are not actually different, indicated by p>.05)

Performing T-tests

5. All of data set 1 All of data set 2 For the purposes of this class a 2 tailed T-test is preferred (fill in with “2”) There are two possibilities for the type of T-test: 1) Most will be two sample unequal variance (fill in with “3”) 2) If the two groups are “paired” meaning taken from the exact same source before and after an experimental treatment fill in with “1”.

NOTE Remember that you should be directly referring in your conclusion to BOTH your graphs as well as the statistical tests your have performed.