Experimental Design and Statistical Analysis:
Bt Corn, Lignin, and ANOVAs

Part IV—"Results—Tables"

by
Eric Ribbens
Department of Biological Sciences
Western Illinois University

Here are two tables of results from the paper:

Table 1. Lignin content (% ± SEM) in different
hybrids of corn, grown in a plant growth room...
    Bt Corn Non-Bt Corn  
Company Event Hybrid % Lignin Hybrid % Lignin P
Novartis Bt11 N7590Bt 7.2 ± 0.10 N7590 4.8 ± 0.14 0.00001
Novartis Bt11 N67-T4 6.3 ± 0.25 N67-H6 3.9 ± 0.15 0.00175
Novartis Bt11 N3030Bt 7.0 ± 0.22 N3030 4.4 ± 0.22 0.00003
Novartis Bt11 NC4990Bt 6.6 ± 0.18 NC4880 3.4 ± 0.7 0.00020
Novartis Bt11 NK4640Bt 6.3 ± 0.14 NK4640 3.2 ± 0.12 0.00001
Novartis 176 Maximizer 4.0 ± 0.15      
Pioneer MON810 P31B13 6.0 ± 0.24 P3223 3.2 ± 0.18 0.00032
DeKalb MON810 DK647Bty 6.2 ± 0.25 DK647 4.4 ± 0.22 0.00174
DeKalb MON810 DK679Bty 6.6 ± 0.11 DK679 3.8 ± 0.10 0.00005
DeKalb MON810 DK626Bty 6.1 ± 0.20 DK626 3.2 ± 0.18 0.00006


Table 2. Lignin content (% ± SEM) in different hybrids of corn, grown in the field...
    Bt Corn Non-Bt Corn  
Company Event Hybrid % Lignin Hybrid % Lignin P
Novartis Bt11 N7590Bt 7.4 ± 0.15 N7590 5.2 ± 0.11 0.00007
Novartis Bt11 N67-T4 7.1 ± 0.22 N67-H6 4.5 ± 0.14 0.00082
Novartis Bt11 NC4990Bt 7.7 ± 0.06 NC4880 4.8 ± 0.22 0.00033
Novartis Bt11 NK4640Bt 7.9 ± 0.10 NK4640 4.9 ± 0.09 0.00001
Novartis 176 Maximizer 5.9 ± 0.13      
Pioneer MON810 P32P76 6.8 ± 0.14 P32P75 4.8 ± 0.22 0.00016
Pioneer MON810 P31B13 7.0 ± 0.04 P3223 4.9 ± 0.13 0.00007
Dekalb MON810 DK626Bty 6.8 ± 0.15 DK626 5.1 ± 0.12 0.00085

Questions:

  1. Why do you think they tested different varieties of corn in the growth room vs. in the field?
  2. Examine Tables 1 and 2.  What does SEM mean in the title?  How is SEM determined?  Why is SEM a poor measure of variability?  What should have been reported instead and why?
  3. What statistical test do you think they used to produce the P values?  What do the P values mean?  What information should have been reported but is missing?
  4. Overall, do you think there are differences between the three different types of genetic modifications (Bt11, 176, MON810)?  What evidence can you identify to support your conclusion?
  5. What statistical test should have been used on the six varieties of corn for which they have both modified and non-modified varieties tested in both the field and the growth room?
  6. The authors also report that "The average diameter of the vascular bundle and surrounding lignified cells in Bt corn was 21.5 ± 0.84 um, whereas that of non-Bt corn was 12.4 ± 1.14 um."  Is this useful information?  If so, how?  What are possible implications?
  7. What kinds of ecological implications might modifications in lignin content have?  What research should be done next?  What suggestions do you have for other experiments and comparisons that should be made to improve this research paper?


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