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I'm completely lost as to how to set up my data and what test to run. Could someone help?

NateB

I'm new to JMP and statistics. I just collected the first round of data for my masters research and am at a loss on how to analyze it. I have eight plant species, from which I made four concentrations of leachate (1.87, 3.75, 7.5, and 15g/25ml). The leachate was was used to test germination inhibition (each concentration was tested on four replicates for each plant for a total of 128 data points). Just by looking at the data, it seems clear that the amount of inhibition varies by both concentration and species. A simple Y by X showed significance with concentration. However, I'm looking to test whether or not each species at each concentration is significantly inhibiting germination. I'm at a loss on what to do.

Accepted answers

Mark_Bailey

I hope that you realize that you put 'the cart before the horse.' The design of your study should have been for the analysis to follow. Collecting data by any means and then wondering about how to analyze it is risky, at best.

Set up data columns for each factor (Species, Leachate Concentration) and the response. Each row is one observation, so enter the replicate observations on separate rows. Then select Analyze > Fit Model. Select Species and Leachate Concentration and click Macros > Full Factorial. Select the response column and click Y. Click Run.

Come back when you get this far to ask about interpretation.

Mark_Bailey

You described your study but you did not show your design in the beginning. Your description led me to believe you could model/test the interaction effect but you cannot. The Singularity Report in one of your pictures highlights that you model is over-specified. So run the analysis again without the cross term and see what happens.

All comments

Mark_Bailey

Come back when you get this far to ask about interpretation.

NateB

Thank you for your response! I now see the type of output for which I was looking! Both Species and Concentration are significant. However, the LS Means Student's T Test (with the connecting letters) as well as Tukey's test show that there is no statistical difference between species or concentrations. I'm not sure how this can be if both are deemed significant predictors of germination.

Mark_Bailey

Can you post a picture of the results to which you are referring?

NateB

See attached. I believe the problem is stemming from the LSM being taken from the species/concentrations as a whole group and not species by concentration (of which there seems to be an obvious significance). However, when I use Fit Model with Germination as the Y and Species, Concentration, and Species*Concentration as the model effects, no discernible information is in the output (I've attached an image of this as well).

Concentration Connecting Letter Report.jpg

Whole Model and Species.jpg

Species, Concentration, and Species*Concentration.jpg

Species Connecting Letter Report.jpg

LSM for Species and Concentration.jpg

Concentration.jpg

Whole Model ANOVA.jpg