Ridge parameter (Stef van Buuren, 15 February 2013)
The paper by Hardt, Herke and Leonhart is a welcome addition to the literature. It warns against simplistic approaches that throw just anything into the imputation model. While the imputation model is generally robust against including junk variables, the paper clearly demonstrates that we should not drive this to the edge. In general building the imputation model requires appropriate care. My personal experience is that it is not beneficial to include more than -say- 25 well-chosen variables into the imputation... read full comment
Comment on: Hardt et al. BMC Medical Research Methodology, 12:184
erratum (John McGrath, 02 August 2012)
This commentary serves to point out that in the results section (p.7) of the manuscript, we (the authors) incorrectly described the calculation of specificity of VIA for the 3-class model. The corrected text (below) describes a specificity of 0.65 versus 0.57. The calculation correction is also... read full comment
Comment on: Gaffikin et al. BMC Medical Research Methodology, 7:36
Correction (Therese Andersson, 02 August 2012)
Equation 12 contains errors. In the equation k_min should be replaced by k_1, k_max with k_K and k_K-j with k_K-j+1. Below equation 12, in the description of lambda_j, k_K-j should again be replaced with k_K-j+1. We would like to thank Dr. Finian Bannon at the N. Ireland Cancer Registry for pointing out these errors. read full comment
Comment on: Andersson et al. BMC Medical Research Methodology, 11:96
Update on methodology for NSW Ministy of Health telephone surveys (Margo Barr, 24 June 2012)
As referenced in the article landline random digit dialling (RDD) have been the method of choice for the telephone based population health survey conducted by the NSW Ministry of Health over the last decade. However because of the increase in mobile phone ownership the methology was modified to include mobile only persons using an overlapping duel-frame design in 2012. The methodology was developed in collaboration with the Centre for Statistical and Survey Methodology at the University of Wollongong. A full description of the methods and preliminary findings will be available soon. read full comment
Comment on: Liu et al. BMC Medical Research Methodology, 11:159
Quantum Biophysical Semeiotics plays a central role in predicting intracranial findings on CT-scans. (Sergio Stagnaro, 02 December 2011)
in order to recognize, among individuals involved by suspected traumatic brain damage, those who really is suffering from such a disorder, physicians nowadays can utilise Quantum Biophysical Semeiotics (1-4).
For instance, in health, light digital pressure, applied upon the closed eye, brings about gastric aspecific reflex (= both stomach fundus and body dilates) after a latency time of 8 sec.
On the contrary, in presence of a pathological condition latency time results smaller, in relation to the seriousness of underlying disorder.
An awful number of other signs allow doctor to make a correct differential diagnosis.
1) Stagnaro S., Percussione Ascoltata degli Attacchi Ischemici Transitori. Ruolo dei Potenziali... read full comment
Comment on: van der Ploeg et al. BMC Medical Research Methodology, 11:143
Further early references to sample sizes with fixed number of clusters (Michael Campbell, 12 September 2011)
Hemming et al (2011) give a useful review of sample size calculations with a fixed number of clusters. As they acknowledge their equations (17) to (19) are derived from Donner and Klar (200). I would like to point out the issue of fixed number of clusters was also discussed by Campbell (2000) that the authors’ equation (13) was first given as equation (2) in that paper and as equation (9.7) in Machin and Campbell (2005).
Campbell MJ Cluster randomized trials in general (family) practice research. Statistical Methods in Medical Research 2000, 9; 81-94
Donner A and Klar N. Design and analysis of cluster randomized trials. London, Arnold 2000
Machin D and Campbell MJ Design of Studies for Medical... read full comment
Comment on: Hemming et al. BMC Medical Research Methodology, 11:102
Two errors in this article? (Emma Friesen, 04 July 2011)
I can't find a definition for FORM in the article. it appears for the first time in the Method section on page 3 but does not have a definition. Is there one?
Also, there appears to be an error in Table 1, in the cell combining "Consistency" and "D Poor". It says 'Evidence is consistent' however it should read 'Evidence is inconsistent'. read full comment
Comment on: Hillier et al. BMC Medical Research Methodology, 11:23
Standard measures of differences between outcome rates are problematic for identifying subgroup effects (James Scanlan, 08 June 2011)
White and Elbourne address the way that interaction tests are affected by whether one compares relative changes in risk of an outcome, relative changes in risk of the opposite outcome, absolute changes in outcome rates, or odds ratios. They recommend a conservative approach to identifying interaction that involves examining the measure that is least likely to show a statistically significant subgroup effect.
The fact that, for example, when an intervention reduces one adverse outcome rate from 12.7% to 5.0% and another from 21.7% to 10.0%, whether an interaction test finds a statistically significant difference between the two changes may depend on what measure of change is employed suggests that something may be amiss with interaction tests generally.
More... read full comment
Comment on: White et al. BMC Medical Research Methodology, 5:15
Competing Interests? (William Anderson, 31 May 2011)
I wonder if it is correct for the authors to state they have no competing interests given the strong association with Complementary and Alternative Medicine read full comment
Comment on: Walach et al. BMC Medical Research Methodology, 6:29
Law & Kaldor method (Ian R White, 25 March 2011)
This article quotes me as saying (in reference 13) that the Law & Kaldor method is likely to be biased towards the null. But in fact reference 13 illustrates a far worse situation: data were simulated with no treatment effect, yet the Law & Kaldor method estimated an "adjusted" hazard ratio of 1.48 (95% CI 1.44 to 1.52). By contrast, methods based on a structural model have the highly desirable property of being unbiased under the null. read full comment
Comment on: Morden et al. BMC Medical Research Methodology, 11:4
regression method of "Peter" (Rainer Beier, 15 March 2011)
It is always a very strong problem for analysing meta-analysis correctly additionally for heterogeneity. In my oppinion the regression model of Peter is the best way to detect publication bias for binary data because it depends on the sample size of the studies, where the sample size is weighted by a function of sample size as described in this article. All other regression models for detecting publication bias do not consider the problem of sample size. But it is very important for investigating meta analysis to consider the sample sizes of the studies included in a meta analysis where small studies with a greater effect could be included compared with larger studies included with a lower effect. Additionally these detecting models do not work if high heterogeneity is given, but in this... read full comment
Comment on: Moreno et al. BMC Medical Research Methodology, 9:2
Correction to typographical error in figure 1 (Sarah Cockayne, 18 October 2010)
Since the paper has been published the authors have noted that there is a typographical error in figure one. The words 'intervention' and 'control' have accidentally been put in the wrong box. It should read allocated to control (n=250) allocated to intervention (n=788). read full comment
Comment on: Cockayne et al. BMC Medical Research Methodology, 5:34
Comparisons of the sizes of health inequalities must be based on measures that are unaffected by the prevalence of an outcome (James Scanlan, 22 September 2010)
Jackson et al. explore some complex issues concerning the possibility that differences in the administrative structures of populations may confound cross-country comparisons of geographic health inequalities. But the authors overlook a fundamental problem with standard comparisons of health inequalities that exists irrespective of the issues they raise – specifically, that the measures underlying those comparisons tend to be affected by the overall prevalence of an outcome. Most notably, for reasons inherent in the shapes of distributions of factors associated with experiencing an outcome, the rarer the outcome, the greater tends to be the relative difference in experiencing it and the smaller tends to be the relative difference in avoiding it.[2-7] Thus, other things being... read full comment
Comment on: Jackson et al. BMC Medical Research Methodology, 10:74
Clarification - Regulatory cases (Fujian Song, 31 August 2010)
Thanks Dr. Eric Turner (Portland VA Medical Center) for sending me (Fujian Song) an email to explain US FDA regulatory process. I found it very helpful. After obtaining Eric's agreement, this clarification is pasted as below for other readers of the article:
"Fujian, I was just looking back at the paper you first-authored in BMC Research Methodology and noticing Figure 1. It shows regulatory authorities first receiving information on a clinical trial after inception and after the data have been analyzed and written up. That's *partly* true. In the US, the FDA gets involved at two points in time, once before inception, and once after trial completion.
The before-inception stage is called an IND application (which stands for Investigational New Drug). Before a drug... read full comment
Comment on: Song et al. BMC Medical Research Methodology, 9:79
RCTs and Meta-analysis as Knowledge Sources (Vance W Berger, 03 August 2010)
Mickenautsch’s article  provides an interesting endorsement of systematic reviews as a method to unite analytic and synthetic knowledge acquisition. There are a few issues that merit further discussion, such as 1) clarifying the basis for the criticism of evidence-based medicine (EBM), 2) considering whether or not all trials should be grouped together as providing equally compelling information and 3) questioning the merits of meta-analysis itself.
After quoting sources asserting that EBM through randomized control trials (RCTs) provides the best evidence, Mickenautsch raises the criticism that EBM claims to have “unique access to absolute scientific truth” which “devalues and replaces knowledge sources of other types.” This criticism does not... read full comment
Comment on: Mickenautsch BMC Medical Research Methodology, 10:53
proof of assumption done in the letter posted on 14th of April (Rainer Beier, 23 July 2010)
In addition to my posted letters on 14th of April the proof of the assumption is given as follows:
Let p1= P(E+/K+) and p2=P(E-/K+) be the being the well known probabilties of diseased patients being exposed and not exposed.Then the following 95% CI for the true value log(NNE) = log(1/(p1-p2)) is given as follows:
So the 95% confidence interval for NNE is now given as follows:
The estimate of NNE was considered as a continious function of two variables f(p1^,p2^) in IR2
Now we have to compare the upper and lower limits of the confidence interval above with the well known confidence interval... read full comment
Comment on: Hildebrandt et al. BMC Medical Research Methodology, 6:32
Addition to my letter "confidence interval for NNE (Rainer Beier, 23 July 2010)
In the following a simulation of the problem explained in my first letter to this article posted on 14th of April:
The simulation is done with the statistical program R where k is the difference of the upper ends of my suggestion for calculating confifidence intervals and done in the article and v is the difference of the length of the two kinds of calculating confidence intervals with one million trials on the interval (0,1) as follows:
> v=k-j... read full comment
Comment on: Hildebrandt et al. BMC Medical Research Methodology, 6:32
Please Download the Latest Version (Tom Trikalinos, 09 July 2010)
The installer included with this publication as supplementary material is dated; please download the latest version at: http://tuftscaes.org/meta_analyst/. Thank you. read full comment
Comment on: Wallace et al. BMC Medical Research Methodology, 9:80
Clarification of methodology (Sue Walker, 21 June 2010)
We wish to clarify the selection of countries we included in our analysis of drowning deaths. To ensure statistical stability in the calculation of percentages, we included those countries with 20 or more reported unintentional drowning deaths, not more than 20 as indicated in the methodology. read full comment
Comment on: Lu et al. BMC Medical Research Methodology, 10:30
confidence intervals for NNE (Rainer Beier, 14 April 2010)
The confidence intervals for NNE computed in this article were computed by inverting the lower and upper end confidence intervals for ARI. This confidence intervals are very wide. My suggestion is to compute the confidence intervals like these for the RR using (log(1/ARI^) as an estimate for log NNE. Then you have to compute the confidence interval for this log estimate and after this using the exponentialfunction to compute the upper and lower ends for the confidence intervals for NNE. E.g in table 5 we get a 95% CI as follows: 101-148. This confidence interval is much more closer to 122.37 instead of 69.55-508.69 . The estimate log(1/ARI^) could be handled like a continious function of two estimates. read full comment
Comment on: Hildebrandt et al. BMC Medical Research Methodology, 6:32
GREAT ( AND WORTHY) EFFORT (Vinícius Ynoe Moraes, 22 March 2010)
This is a very interesting manuscript, very creative and relevant. It is a fact that regarding to treatment issues we do not have the access to an up-to-date systematic review, in some cases. Therefore, this paper strenghtes a personal belief that we can rely on the largest trial, specially if it respects the treatment effect issues and (what i believe to be THE ISSUE) HAS AN EXPLICT AND CLEAR prevous power anaysis. Thanks for this pleasant reading and congratulations. read full comment
Comment on: Glasziou et al. BMC Medical Research Methodology, 10:23
Previous IPD diagnostic and prognostic reviews (Bob Phillips, 17 March 2010)
Diagnostic tests and prognostic variables have been subject to previous IPD meta-analysis. Some of these include:
Royston, P., M.K. Parmar, and R. Sylvester, Construction and validation of a prognostic model across several studies, with an application in superficial bladder cancer. Stat Med, 2004. 23(6): p. 907-26.
Fibrinogen Studies Collaboration, Plasma Fibrinogen Level and the Risk of Major Cardiovascular Diseases and Nonvascular Mortality: An Individual Participant Meta-analysis. JAMA, 2005. 294(14): p. 1799-1809.
Trivella, M., et al., Microvessel density as a prognostic factor in non-small-cell lung carcinoma: a meta-analysis of individual patient data. Lancet Oncol, 2007. 8(6): p. 488-99.
Mant, J., et al., Systematic review and individual... read full comment
Comment on: Broeze et al. BMC Medical Research Methodology, 9:22
Easier to change publishing systems than to change language (John Hilton, 01 February 2010)
Persuading publishers, institutions, societies, and others to agree to abolish possessive eponyms would take time and a fair amount of effort, when perhaps there are bigger issues for those groups to tackle. Furthermore, it requires a change to everyday language that many will ignore or resent. If the change from possessive to non-possessive forms is happening anyway, why push it? Perhaps a better solution to the underlying issues of search accuracy and confusion would be promote the embedding of medical coding systems in publishing and searching. This would have the advantage of covering non-English language variants and other naming variations. read full comment
Comment on: Jana et al. BMC Medical Research Methodology, 9:18
The relative importance of variables in predictive models: bootstrapping, p-values, and sensible modelling strategies (Ewout Steyerberg, 16 December 2009)
The development and validation of prediction models poses many challenges. Determining the relative importance of variables for inclusion in such models is an extremely tough research question, which was addressed recently by Beyene et al .
Previous work on the relative importance of predictors in a model has shown very worrying results. For example, simulations with stepwise selection methods showed that the specific set of predictors in a model was very unstable, and that the rank order of importance of predictors in a selected model was even more unstable .
There are several major problems with the procedures that the authors of the recent BMC paper propose, apart from general suboptimal modelling such as by dichotomizing all predictors . First, the... read full comment
Comment on: Beyene et al. BMC Medical Research Methodology, 9:64
Country of origin of articles (Karen Shashok, 23 September 2009)
Dr Bliziotis, in his reviewer's comments, noted that there are differences in "how each search engine identifies an article as originating from a country" in each database (Medline and SCI). This is an important potential confounder because international collaboration is increasingly common. I hope the authors will find a way to replicate this study taking into account the country of origin of the corresponding author and each co-author.
firstname.lastname@example.org read full comment
Comment on: Benamer et al. BMC Medical Research Methodology, 9:26