Biometry
Stat 412

Lab Assignment #2

Important: Read all of this handout before starting!!!

Goals:

1) Entering, editing, saving and verifying raw data
2) Exploring basic statistics of the data
3) Graphing data

 

Assignment: implement the following procedures using MINITAB.

A. Data entering, editing, and verification

  1. Use the data sheet from your survey team plus those of two other teams to enter the data for the circumference of Doug Fir trees into MINITAB. Enter each transect into a separate columns (e.g., C1,C2, C3) and label them accordingly. There should be a total of n=5-20 numbers per column.
  2. After the data have been entered save the worksheet.
  3. Print the data.
  4. Verify the printed data against the raw data.
  5. Edit any mistakes you may have made by changing the values in the data window.
  6. Save the fully verified data.

B. Exploring the data: complete for all data

  1. First, convert all data to SI units, in this case meters  (e.g., 1 in = 0.0254 m) using the  LET command).
  2. Stack the data using the stack command: 
     

MTB > Stack 'Tran1' 'Tran2' 'Tran3' c4;
SUBC> Subscripts c5;
SUBC> UseNames.
 

  1. Look at the statistical distributions of each transect using low-resolution histograms. First, switch to character graphs by typing in the command GSTD, then type in the histogram command HIST C1. Next, make histograms for using a high resolution histogram by typing the command GPRO then HIST C1). Finally, make a grouped histogram using the menu system (MTB > Histogram C4; SUBC> Distribution C5; SUBC> Normal; SUBC> Overlay.)
     
  2. Answer the following questions: What can you conclude about the statistical distribution of the data? What does this tell you about the size patterns of Douglas Fir trees?
     
  3. Compute the mean, variance and standard deviation "by hand" using the AVERAGE, SUBT, RAISE, and SUM commands for each data column (see class handout); check with the MEAN and STAN command.
     
  4. Answer the following questions: Which transect is more variable in abundance? What does this tell you biologically?

C. Graphing the data: complete for all data

  1. Now let's create a graph to plot the data. Using the menu select the Graph » Interval plot option. Select the one-Y with groups option. Under Y variable type C3 or double-click with the left mouse button on the fir column on the left. Under Group variable type C64or double-click with the left mouse button on the transect column on the left. You should also add an X axis label such as "Transect" and a Y axis label such as "Mean circumference (m)" and finally a title such as "Douglas Fir trees at WSUV, 2007" When you are done click on the OK button and your graph will be created. It should look similar to this.

    2.  

  2. After the graph has been created you can customize it, as demonstrated in class, and then print it. Keep in mind that others may be printing graphs so you should add you name or group number to each graph title so they don't get confused.

    3.  
  3. Answer the following questions: How does mean size vary among transects? How does the variability as measured by the standard error vary? Can you think of a hypothesis that might explain these patterns?

This assignment is due NEXT Monday, Sept. 17, in class

Also see: Assignment #2 in Hawai'i