Reviewer's report
Title:Effect of a multispecies probiotic supplement on quantity of irritable bowel
syndrome-related intestinal microbial phylotypes
Version: 2Date:7 August 2010
Reviewer: Giorgio Bedogni
Reviewer's report:
Major Compulsory Revisions
1. The choice of a mixed model to study the effect of treatment is a very good
one. However, principal component analysis (PCA) as it is currently performed
does not take into account the longitudinal nature of the data. The outcome of
PCA should be a “change”, as it is for the mixed model. I also do not understand
why the 3-month and 6-month data were analyzed together.
2. Multiple outcomes are evaluated. This implies a greater risk that some of the
findings may be due to chance. This is even more important in view of the fact
that the data obtained from this study were used to test many (arguably not
pre-specified) hypotheses (published in different Journals). Please, note that I am
not saying that this should not be done but that it should be done with great
caution and making very clear the hypothesis-generating feature of the analysis.
3. The issue discussed at point 2 is reinforced when subgroup analysis is
performed. With all due caution, the role of the subgroups may be studied inside
the regression models.
Minor Essential Revisions
4. Please, specify in detail the employed mixed model. I suppose that it included
at least treatment, time, and a timeXtreatment interaction as covariates and the
patient as random intercept.
Discretionary Revisions
5. The part saying that the mixed-model is “like” RM-ANOVA should be removed.
This is useful to make people understand what the mixed model does but
RM-ANOVA is poorly equipped to deal with longitudinal data, e.g. McCulloch CE.
Repeated measures ANOVA, RIP. Chance 2005;18:29-33.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests
Reviewer's report
Title:Effect of a multispecies probiotic supplement on quantity of irritable bowel
syndrome-related intestinal microbial phylotypes
Version: 2Date:7 August 2010
Reviewer: Giorgio Bedogni
Reviewer's report:
Major Compulsory Revisions
1. The choice of a mixed model to study the effect of treatment is a very good
one. However, principal component analysis (PCA) as it is currently performed
does not take into account the longitudinal nature of the data. The outcome of
PCA should be a “change”, as it is for the mixed model. I also do not understand
why the 3-month and 6-month data were analyzed together.
2. Multiple outcomes are evaluated. This implies a greater risk that some of the
findings may be due to chance. This is even more important in view of the fact
that the data obtained from this study were used to test many (arguably not
pre-specified) hypotheses (published in different Journals). Please, note that I am
not saying that this should not be done but that it should be done with great
caution and making very clear the hypothesis-generating feature of the analysis.
3. The issue discussed at point 2 is reinforced when subgroup analysis is
performed. With all due caution, the role of the subgroups may be studied inside
the regression models.
Minor Essential Revisions
4. Please, specify in detail the employed mixed model. I suppose that it included
at least treatment, time, and a timeXtreatment interaction as covariates and the
patient as random intercept.
Discretionary Revisions
5. The part saying that the mixed-model is “like” RM-ANOVA should be removed.
This is useful to make people understand what the mixed model does but
RM-ANOVA is poorly equipped to deal with longitudinal data, e.g. McCulloch CE.
Repeated measures ANOVA, RIP. Chance 2005;18:29-33.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests
Please review this paper.
user
Reviewer's report
Title:Effect of a multispecies probiotic supplement on quantity of irritable bowel
syndrome-related intestinal microbial phylotypes
Version: 2Date:7 August 2010
Reviewer: Giorgio Bedogni
Reviewer's report:
Major Compulsory Revisions
1. The choice of a mixed model to study the effect of treatment is a very good
one. However, principal component analysis (PCA) as it is currently performed
does not take into account the longitudinal nature of the data. The outcome of
PCA should be a “change”, as it is for the mixed model. I also do not understand
why the 3-month and 6-month data were analyzed together.
2. Multiple outcomes are evaluated. This implies a greater risk that some of the
findings may be due to chance. This is even more important in view of the fact
that the data obtained from this study were used to test many (arguably not
pre-specified) hypotheses (published in different Journals). Please, note that I am
not saying that this should not be done but that it should be done with great
caution and making very clear the hypothesis-generating feature of the analysis.
3. The issue discussed at point 2 is reinforced when subgroup analysis is
performed. With all due caution, the role of the subgroups may be studied inside
the regression models.
Minor Essential Revisions
4. Please, specify in detail the employed mixed model. I suppose that it included
at least treatment, time, and a timeXtreatment interaction as covariates and the
patient as random intercept.
Discretionary Revisions
5. The part saying that the mixed-model is “like” RM-ANOVA should be removed.
This is useful to make people understand what the mixed model does but
RM-ANOVA is poorly equipped to deal with longitudinal data, e.g. McCulloch CE.
Repeated measures ANOVA, RIP. Chance 2005;18:29-33.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests
assistant