Artificial Selection Lab- Data Analysis
For the purposes of our lab report, we need to be able to show our data in an organized and visually pleasing
way. Additionally, we need to be able present it in a way that we can easily interpret the data and use those
results to support or reject our hypothesis. How do we do this? How can we best present the data that we
collected and what are the best analysis tools that can help us interpret the data?
Presentation of the Data:
The presentation of data is often done in an organized data table that is clearly labeled with the proper
headings. Because all the classes are using the same data we do not need to include the data table in your lab
report. However, it is important that you save a copy of the Excel Spreadsheet on your hard drive and
organize the data in the spreadsheet in way that you and others can understand.
Graphs make a great way to visually represent data from our data table. Graphing the data can allow us to
spot trends that exist or allow us to easily compare one set of data to another. Since we have a fairly large
amount of data that we have collected, we can create a graph called a histogram. A histogram is a bar graph
that combines the data into groups we call bins. The bins usually represent the data that falls within a certain
range we are measuring, such 0-5, 6-10, and 11-15. It is often necessary to play around with how we group
our data to see which graph best shows what we are looking for. This graphical representation usually makes
it easier to see trends in the data. Refer to page S12 of the Chapter 3: Quantitative Reasoning in AP Biology
handout (link can be found under Lab Report Help under AP Biology Links) to find an example of a histogram.
How to Create a Histogram: When creating a histogram, the data
must first be rearranged by sorting it into the specific bins you create.
In a separate column near the data you want to graph, create a
OR
column labeled Bin Limits. Determine how large your bins will be and
fill this column with the data groups that you choose. Two examples
of different sized bins are given on the left. You are now ready to sort
your data. Under the Data tab at the top of Excel, look for the Data
Analysis* function on the right hand side. Within this function,
choose the Histogram analysis tool from the list given.
Bin Limits
5
10
15
20
25
30
35
Bin Limits
10
20
30
40
50
60
70
Input Range: Select the data you would like to graph (Ex:
number of trichomes in the parent generation)
Bin Range: Select the Bin Limit numbers that you created above
Output Range: Choose a convenient cell on the spreadsheet
where the resulting data will be created.
*If the data analysis function is not present, Analysis Toolpaks must be enabled in Excel. Look under the File
tab. Click Options. Click Add-Ins. Click Go at the bottom of the page. Choose both Analysis ToolPaks. Click OK
Once Excel has populated your bins with the data, you can re-label the bin limits as a range.
However, often you must change the format of the data you enter into the cells. To do this,
select the bin limits column that the computer created, click on the Home tab and choose the
Text number format from the drop down menu (usually the format is list as General by default).
Enter the bin ranges you choose. An example is to right.
Bin Limits
0-5
6-10
11-15
16-20
21-25
26-30
31-35
You are now ready to create your graph. Select the all the new data columns that the computer
created in the steps above. Under the Insert tab, choose a 2D column graph from the list. The
histogram should now be present. Be sure to use the Chart Layout Tools to add a graph title and axis labels.
How to perform a t-test on Excel: To determine what data we want to compare and what type of analysis we
need to perform to do this comparison, we first need to know the purpose or question of our lab? Why did
we grow our Fast plants, “select” for the plants we did and then plant those seeds separately from the “nonselected” plants? Once we understand what it is we are looking for, we can use the proper tools to find the
answer. Use the Analyzing and Evaluating Results section of your lab (pg. S23; also online under AP Biology
Handouts) to help guide your questions that pertain to the analysis of your results.
The simple statistical tests that we will be using can be performed directly in the Excel Spreadsheet that we
created. First, we can simply find the mean of our data sets using the average function. While the average is
useful in data comparison and tells us a lot, we often can’t tell how significant our results (the mean) are. By
performing a statistical test called a t-test, we can determine whether the means of two different sets of data
are the result of random chance or if something significant was done to the data of the experimental group to
achieve the results we did. Follow the instructions outlined of the webpage entitled Statistical Analysis listed
under AP Biology Links, Lab Report Help. The second part of the discussion will walk you through how to
perform a t-test in Excel.