Re: Doesn't a t-test work here?

jgpowers@xxxxxxxxx wrote:
Hello,
I am a biologist attempting to publish in a Scientific Journal. I
used t-tests to analyze some of my data and one of the reviewers made
a comment about this being inappropriate. This same reviewer made
other comments that led me to question whether or not he really
understood what was going on, but I wanted to get some input on
whether or not a t-test would be appropriate in this situation. My
statistics background is limited, I did take a class about 4 years ago
in statistics, but since I didn't need the information right away, the
majority of it left my brain almost immediately.
Reviewer's exact quote:
"A T-test or Anova are really for pairwise comparisons and cannot be
used for comparisons of multiple samples such as this. "

My experimental set up:
Leaves of a plant were treated with 1
of 9 different compounds, or one compound that served as a control.
Each of these compounds produced a certain amount of Green fluorescent
light when ultraviolet light was shown onto the leaves. This level of
light could be quantitatively measured as photons of light emitted per
second per square centimeter. Each compound was placed onto 10
different leaves and measurements from each of these treatments were
taken. The 10 measurements for each compound was compared to the 10
control measurements to determine if the compound increased
fluorescent light emitted at a statistically significant level as
compared to the control. I thought that to do this a T-test or
possibly an Anova was an appropriate way to make this analysis. Again
I wanted to compare Compound X with Control, Compound Y with control,
Compound Z with control, and so on. I do not care how Compound X
compares with Compound Y.

Am I correct here?
In a word, no, especially if you set this up as a pairwise comparison. Neither is the reviewer, but I'll give them the benefit of the doubt because they're being quoted out of context. On the face of it, the first half of the sentence (ANOVA really for pairwise comparisons) is incorrect, though I can see what they are trying to get at. There is some truth to the second half (naive use of ANOVA is not appropriate for multiple comparisons).

If so how would you respond to the reviewer?
Maybe start by reading about multiple comparisons. (Perhaps someone else more familiar with literature in your field could suggest a reference. Otherwise, Google should be your friend.) It's hard to say exactly how you should be doing your analysis, since some details of your experimental setup are lacking. Were the control measurements on the same 10 leaves in each case? Were the leaves all selected from the same plant? More generally, what scheme was used to assign treatments to leaves?
.

Relevant Pages

  • Re: Doesnt a t-test work here?
    ... "A T-test or Anova are really for pairwise comparisons and cannot be ... Leaves of a plant were treated with 1 ... of 9 different compounds, or one compound that served as a control. ...
    (sci.stat.edu)
  • Re: Doesnt a t-test work here?
    ... Leaves of a plant were treated with 1 ... of 9 different compounds, or one compound that served as a control. ... The 10 measurements for each compound was compared to the 10 ...
    (sci.stat.edu)
  • Doesnt a t-test work here?
    ... "A T-test or Anova are really for pairwise comparisons and cannot be ... of 9 different compounds, or one compound that served as a control. ... If so how would you respond to the reviewer? ...
    (sci.stat.edu)