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Biology LibreTexts

Laboratory Exercise- Statistics and Graphing

Laboratory Exercise

Descriptive Statistics and Graphing

Campus students should answer the questions below on the answer sheet. Online students should return to the learning modules to submit answers to these questions.

Some of the questions require you to create graphs. Online students should insert the graphs in the document that contains their answers. In Word 2003 and earlier (and most other word processors), this can be done by clicking Insert, Picture, From File, then browse for the file. In Word 2007 click Insert, Picture, then browse for the file.

  1. Explain why a bar graph is used for the mammal data. (See Bar Graphs in the reading assignment for this exercise.)
  2. Explain why a line graph is used for the pH data. (See Line Graphs in the reading assignment for this exercise.)
  3. Explain why a scatter plot is used for the bird species data. (See Scatter Plots in the reading assignment for this exercise.)
  4. Suppose that a researcher was interested in how long it takes people to recover after exercise. She asked five test subjects (people) to run for 30 minutes on a treadmill and then measured the amount of time that it took for the heart rates to return to normal. A) What kind of graph would be most useful for plotting the recovery time of each person? B) Why?
  5. Calculate the mean and median for the pH data (line graph data). Use 3 significant digits for your answer. (See Rounding and Significant Digits in the reading assignment for this exercise.)
  6. Which measure(s) of central tendency do you think is (are) good to use for the pH data? (Answer Mean, Median, or Either.) Explain your answer to this question. (See Central Tendency and Which to Use- Some Disadvantages of Each in in the reading assignment for this lab.) ) When answering this question, students often say that the data have a bell-shaped curve. However, in order to know if the data have a bell-shaped curve (normal distribution) you would need to plot the number of observations on the Y-axis and pH on the X-axis. It is not necessary to do this. Assume that the data are normally distributed. Click the link above for the answer to this question.
  7. Create three graphs, one for each of the data sets below using Excel or LibreOffice.

    Instructions for creating graphs using Excel

    Instructions for creating graphs using LibreOffice

     

    Data set A - The data below are the number of different species of insects captured in four different oldfields on July 18, 2007. Sampling was done between 10:00 and 11:30 AM. Each field was an abandoned hayfield that had not been mowed for four years.

    Field A - 37 species

    Field B - 25

    Field C - 17

    Field D - 15

    The title of your graph should provide the reader with enough information so that the reader knows exactly what the graph is. This usually requires several sentences. The words "Data set A" are not enough. 

    Be sure that both axes of your graph are labeled. The reader needs to know what the numbers are.

    Data set B - This information is the temperature in Plattsburgh, New York on January 21, 2008. All of the temperatures are negative (below 0 centigrade or below 32 Fahrenheit).

    -16.1 degrees centigrade (Don't forget the negative sign!!!)

    -18.3 degrees C

    -13.3 degrees C

    -6.7 degrees C

    -8.3 degrees C

    -9.4 degrees C

    NOTE- Be sure to put a negative sign in front of the numbers when you enter them into a graphing program because these temperatures are below zero.

    When you plot the temperature data on the Y-axis, the smallest number (-18.3) should go near the bottom of the graph. the largest number (-6.7) should go near the top.

    Be sure that the graph has a detailed title and that both of the axes are labeled. The reader needs to know that the temperature is recorded in degrees Centigrade.

    Data set C - The data below show the body weight of 6 rats given different amounts of growth hormone. Create a line graph of the data. If you use Create A Graph, select XY graph for this data set.

    1. hormone: 0.15 mg     body weight: 29.5 g
    2. hormone: 0.20 mg     body weight: 29.3 g
    3. hormone: 0.25 mg     body weight: 32.0 g
    4. hormone: 0.30 mg     body weight: 35.1 g
    5. hormone: 0.35 mg     body weight: 23.6
    6. hormone: 0.45 mg     body weight: 19.2

      This graph is not a scatterplot. The points should be connected with a line.

      Be sure to label the axes. The reader needs to know that the amount of hormone is recorded in milligrams (or mg) and that body weight is recorded in grams (or g).

    The minimum and maximum values of your X and Y axes should be adjusted so that the data points use most of the space. For example, in data set C above, the body weights vary from 19.2 g to 35.1 g. Make the minimum value for this axis something less than 19.2. Values of 15, 18, or 19 might be good. The maximum value on the axis should be slightly greater than the largest data point (35.1); 36 or 40 might be good for this.

    Do not forget to include units when labeling the axes. For example, if one axis is Body Weight, you should indicate that the units are grams: Body Weight (g).

Statistical Analysis

  1. Use the t-Test spreadsheet prepared for this course and perform a 1-tailed t-test on the mouse weight data in the reading assignment on statistical analysis. Turn in a printout of your spreadsheet analysis. The spreadsheet requires Excel or an Excel-compatible spreadsheet program such as Libreoffice or Numbers. If you do not haveone of these programs installed on your computer, you can download Libreoffice for free at http://www.libreoffice.org. To use Libreoffice, save the spreadsheet to your computer, start Libreoffice and click "Open a document."
  2. Perform a t-test on the pH data (the line graph data) to determine if the pH in the morning (1:00 to 11:00 AM) is different than the pH in the afternoon (1:00 PM to 11:00 PM). A 2-tailed test can be done using the t-test spreadsheet by entering a 2 in cell B2 (column B, row 2). Click here for some examples of statistical analysis using a t-test.
    1. Explain why this is a 2-tailed test. (See 2-tailed test above.)
    2. State the hypothesis being tested for this analysis. Be sure that your hypothesis is for a 2-tailed test. See your answer to the previous question for help with wording.  Click here for more information on constructing a hypothesis.
    3. Based on the results of the t-test, do you accept your hypothesis or do you reject your hypothesis? (See Some Examples of Statistical Analysis Using a t-test.)
    4. Why did you accept (or reject) your hypothesis? [Hint- You must consult the probability from the t-test before you can answer this question.] (See Some Examples of Statistical Analysis Using a t-test).
    5. Attach a printout of your spreadsheet analysis. Be sure that your analysis is for a 2-tailed test. To make it a 2-tailed test, enter a 2 in cell B2 (column B, row 2).