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gopat gopat
wrote...
13 years ago
Greetings,
I conducted an indoor plant rooting test involving 9 treatments (including 1 control).  These tests were repeated by using 2 clones (siblings) and replicated across 2 flats with the plant trays (3" x 3")  in random locations.  Each flat contained 18 test trays with the 2 sibling clones each having 9 treatments.  Each tray contained 3 cuttings.

I scored the rooting results for each tray into 3 categories:
[LIST=1]
[*]The total number of all roots that are longer than 1 mm (abv. "Roots>1mm").
[*]The percent of cuttings with root lengths longer than 20 mm (abv. "%Roots>20mm).
[*]The percent of cuttings that have any roots > 1 mm (abv. "%Rooted).
[/list]

Both flats contain the same tests so in theory, both should have similar results for each clone/treatment.  I need to apply a statistical test that will compare the Flat 1 and Flat 2 values for the SAME clones and provide a P value that the 2 results might be the same.  I was thinking the Fisher Exact|http://en.wikipedia.org/wiki/Fisher%27s_exact_test test would work, but I am not sure... 

Below is the data for the 1 control clone:

Treatment Name    Flat1    Flat2 
%Roots>20mm 0.66 0.66
%Rooted  1   1
Roots>1mm 31 19

Note that the only difference is that the Flat2 samples had 12 less roots than the Flat1 samples.  What statistical test would be appropriate to compare these 2 sets of results?  Please show and explain your results with the P value.
Thanks in advance!
Pat
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12 Replies

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Replies
wrote...
Staff Member
13 years ago
If you have multiple treatments with say 3 repeats for each, use ANOVA; your k value will be 9 (for 9 treatments), you n value will b 3 (for 3 repeats), and your N value will be all the 27 (all together).
- Master of Science in Biology
- Bachelor of Science
gopat Author
wrote...
13 years ago
What a mess!  I meant to clean up the markup but clicked Post instead of Preview.  Where is the "Edit" or "Modify" buttons so I can fix this post?
wrote...
Staff Member
13 years ago
You have to have 75 posts for that Thumbs Down Sign
- Master of Science in Biology
- Bachelor of Science
gopat Author
wrote...
13 years ago
I would like to get my arms around the flat to flat differences for each clone/test first.  Then I will examine how they relate to the other tests. 

Both flats had the same 18 tests (trays) so these common tests "should" be similar.  If there are too many significant differences then the entire test may be invalid...

I ran a single factor Anova test on the Flat1/Flat2 data listed above for the same clone in a Gnumeric Spreadsheet.  See the attached .png file.

Is this the appropriate test for this type of problem?  I think all I care about is the "Between Groups" variation.  The P value is .88, which I assume is for the Between Groups variation.  If I had a 5% level of confidence, I may have to reassess the validity of that test...  How would you interpret the results?
 Attached file 
Thumbnail(s):
wrote...
Educator
13 years ago
This is a relatively easy problem to solve gopat, but I'm not understanding you experiment. Are you trying to find if there is a significant difference in the means of the two groups?

For example:

Group 1 is aged 20-30
Group 2 is aged 31-40

You tested 10 people from each group and got a mean value, say for heart rate... and now you want to find if there is a significant difference in their heart rates.

Is your experiment like this?

First tell me how many treatments you have and how many controls you have. If its like this:

For example:

Males            Control... Treatment 1 2 3
Females       Control... Treatmeant 1 2 3

and for each treatments you have 5 people, then its two way ANOVA. If you did not differentiate between male or female, it's one way ANOVA. ANOVA does both Between and Within Treatments.

gopat Author
wrote...
13 years ago
Using your requirements, I have a control with 8 treatments and 2 groups:

Clone1:  Control(water), and 8 other treatments
Clone2:  Control(water), and 8 other treatments

For each treatment I have 3 test plants per tray, 9 trays per clone and 18 trays per flat
I replicated the above tests in 2 flats...
wrote...
Educator
13 years ago
Gotchya, then you MUST do a two-way ANOVA test.

Do you know how?
wrote...
Educator
13 years ago
Here is an excellent example on how to do it.
 Attached file 
You must login or register to gain access to this attachment.
gopat Author
wrote...
13 years ago
Gee thanks!  I should be able to take it from here...  I will dig into that file and apply it to my case.  I have plenty of homework now!
Pat
wrote...
Educator
13 years ago
That file should be good for your needs no doubt.
gopat Author
wrote...
13 years ago
Hey, this is scary.... 
I just had time to look at your file.  You based your example on Poplar yield stats from 2 different sites...  Well, would you believe that my test was based on poplar shoots using different fertilzer treatments!  I had to look twice when I saw the data. 

Strange prophesy that it would be that useful to me, since I can apply this directly to my situation and other site data.  I am going to digest this some more, then play with your numbers in a Gnumeric spreadsheet to verify that I have it right...  Then I will apply it to my case.

Thanks a ton!
I owe you some trees!
wrote...
Educator
13 years ago
Smiling Face with Open Mouth and Tightly-closed Eyes nice, I hope it helps, thanks for the feedback
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