Review for 10.1186/1471-230X-12-84 (2012)

Reviewer's report
Title:Predicting incident fatty liver at 4.37 year follow up, using simple
cardio-metabolic risk factors at baseline
Version: 1Date:2 April 2012
Reviewer: Richard Lilford
Reviewer's report:
Thank you for sending me this paper from Sung and colleagues.
The study follows a sub cohort of people, representing those that did not have a
fatty liver at the time of an initial screen. The cohort is followed for just over four
years, at which time the ultra-sound scan was repeated to see if fatty liver had
occurred. So the design of the study is to find out which of the patients who
apparently did not have fatty liver at year zero, developed this over about four
years. I have given this design some thought and conclude that it answers a
question of relatively little importance. This is because the question is relevant
only to the follow up of a specific group of people – namely those who have had
a scan which has shown no fatty liver and the doctor is wondering whether the
scan should be repeated after a few years. Moreover, the original scan was done
in a general population (as part of a company check-up). So the cohort studied is
more specific still – a mainly male group of employees give a scan of liver that
returned a normal result. The generation of such a cohort of people who have
had a scan, and then been found negative, is just something that doesn’t often
happen. Since around a third of the whole population have fatty liver it is rather
fortunate that such routine scanning has not been instituted. Furthermore, the
utility of finding a fatty liver is very dubious. For these reasons I am sceptical
about the clinical importance of this study.
I also do not think it has any particular scientific meaning. Granted, there is a
longitudinal element to the study, but it is not at all clear what this teaches us that
we did not already know; why should the risk factors for developing a fatty liver in
a group of different ages be different to the factors for having it at a moment of
time.
My further comments are as follows:
There was no diagram of the ROC curve in my manuscript.
The study could have been greatly strengthened by following up patients both
with and without a fatty liver at base-line, perhaps by sampling from both groups.
This would have enabled the predictive value of base-line characteristics to be
evaluated for three groups of people:
1. Fatty at base-line but reverting to normal.
2. Normal at base-line but becoming fatty.
3. Fatty at both base-line and after four years.
Of course, it would have been necessary to bear in mind (and perhaps examine
for) the possibility that some people with a fatty liver could have changed their
behaviour.
I was surprised there were no drop outs or incomplete data in the data set – one
would have imagined that some people had retired or moved?
On reading the methods question it is not absolutely clear when the various
observations were made. From what is said in the discussion and introduction I
think all the observations and blood tests were done at base-line and then the
patients simply followed up with an ultra-sound. However, the way it is written
this is not crystal clear.
I’m not sure whether any step-wise procedures were used as part of the logistic
regression and whether any imputation was necessary for missing values.
My problem with this paper concerns its rationalé and importance, rather than the
specific features of the statistical analysis and presentation. Therefore I’ve
declined to give specific editorial recommendations. However, a statistician
should review the manuscript if you wish to take it forward.
Yours sincerely
Professor Richard Lilford
Level of interest: An article of limited interest
Quality of written English: Acceptable
Statistical review: Yes, but I do not feel adequately qualified to assess the
statistics.
Declaration of competing interests:
I declare that I have no competing interests.