24/10/2014
Dear Editor,
Thank you for your consideration of our paper. We are grateful to the two reviewers for the time
they have taken to review our paper and their considered comments. We have now modified the
paper according to the suggestions of the reviewers and have prepared a point-by-point response
detailing the ways in which we have responded to particular comments (see below). I hope that you
will now find the paper to be suitable for publication in BMC Obesity and look forward to hearing
from you with a final outcome shortly.
With best wishes,
Dr Adrian Cameron (on behalf of Drs Waterlander and Svastisalee).
Reviewer Comment
[Reviewer 1] Using one method to measure aisle
length of supermarkets across all the countries would
provide reliable results as compared to use of different
techniques as done in this study.
Some part of the discussion and conclusions, are not
directly reported from the results obtained. Lifestyle
factors, though, already known from studies done
elsewhere, are important risk factors in causing an
increase in overweight and obesity, but the study does
not involve obtaining information on these parameters.
Figure legends need to be checked for spacing and
unit for obesity prevalence should be added.
Reference numbers provided in the text are not in line
with the journal requirements. The reference numbers
must be in square brackets, thus the authors need to
change the format of the reference numbers.
Reference style used at the end of the manuscript are
not conforming with the journal guidelines, hence they
Our response
Objective measures (measuring wheel/tape) were
used in the vast majority of stores audited. Only in 9
stores from one region in America (i.e. less than one
third of all American stores, 5% of all stores measured)
was a different method used, and there is no reason to
suspect that the results using this method (calibrated
paces) would have a high degree of error. We believe
that store size has been appropriately measured in this
study and the methods appropriately reported in this
paper.
We completely agree that lifestyle factors such as diet,
physical activity and sedentary behaviour are important
risk factors for overweight and obesity, however ours is
a simple study of retail store size and national obesity
prevalence and therefore does not involve any
measurements of individuals. As we carefully explain
in the introduction and discussion, it is our hypothesis
that store size impacts on some of these lifestyle
behaviours (eating and shopping behaviours) and this
may explain the association between store size and
national obesity prevalence observed. We do not
believe there is any need to further explore this issue
in the paper.
The unit for obesity prevalence (i.e. “%”) is now
included in the Y axis label as suggested.
References numbers have been changed according to
the recommended journal style.
Referencing style has been changed to comply with
journal style.
should be re-done as per the journal requirements
[Reviewer 2]
Paragraph 2 under the ‘Discussion Section,’ involves
some statements that are not directly reported from the
study results. These statements need to be revised.
The results presented in the manuscript, can be better
presented in a table form, for a clearer understanding.
Lifestyle factors, including diet and physical activity,
are important contributors to the obesity prevalence;
hence information on these factors can strengthen the
results of the study and can provide a better picture of
the overall prevalence, rather than just focusing on
body weight data.
The ‘Results’ and ‘Conclusions’ section of the abstract
are not directly reported from the obtained results, as
data on reasons for the association obtained between
average store size length and national obesity
prevalence in the manuscript are not obtained. Thus,
these statements must be re-written.
Sampling method not clearly mentioned.
This paragraph involves a description of the factors in
the three countries with the lowest obesity prevalence
and store size that might explain these observations.
The results of the study naturally only report the
observations on store size and obesity. In order to
place these observations in context, and potentially
explain the findings, it is reasonable to report on
factors such as urban density and infrastructure. We
therefore do not believe that there is any justification
for revising this paragraph.
Given the results section is only one paragraph long
and the main results of the study are already included
as a figure, we do not believe that a table of the few
results presented in text is necessary but are happy to
be guided by the editor on this point.
This study involves an ecological association between
store size and obesity prevalence. There are likely to
be diet-related factors that are responsible for this
association (as per our hypothesis), but we are not
able to include them in our analysis (which is a simple
association between store size and obesity
prevalence). Our discussion focuses entirely on the
lifestyle factors (including those related to transportrelated physical activity) that may be responsible for
the association observed and we therefore feel that
this is covered adequately.
Please also see comment 2, reviewer 1.
Thank you for pointing this out. We have now moved
the sentence that did not refer specifically to the results
obtained in this study from the results to the
conclusions section of the abstract. The conclusions
section now reads: “Conclusions: Explanations for the
association between store size and national obesity
prevalence may include larger and less frequent
shopping trips and greater choice and exposure to
foods in countries with larger stores. Large
supermarkets may represent a food system that
focuses on quantity ahead of quality and therefore may
be an important and novel environmental indicator of a
pattern of behaviour that encourages obesity”
We have added the following paragraph to the
methods section: “Supermarkets were sampled equally
from neighbourhoods within the least and most
socioeconomically disadvantaged areas in Australia,
Denmark, the Netherlands and Canada (Montreal
only). While all auditors were instructed to try to obtain
a sample that was representative of their local area
(Geographically, and in terms of the types/chains of
supermarkets present), no further explicit sampling
criteria were followed. The precise supermarket
retailers included in the audits were a reflection of the
range of chains present in that location. In some
countries this meant only a small number of chains
Sample size and its representativeness - When
selecting a Nationally representative sample to
estimate the Super Market size of a particular country
it should have an adequate number proportionate to
the number of supermarkets in the country or a good
justification as to why the small sample size is in fact
representative of the entire population of supermarkets
in the country.
The representativeness is essential for any ecological
study which are based on population parameters. The
national obesity prevalence is a national figure but the
chosen sample for supermarket size is very unlikely to
have a representation of national figures, given the
variation in the sample size that does not align with the
population of the country or the number of
supermarkets. (Eg. n=8 England with a population of
64 million, n=10 in New Zealand with a population of
4.5 million, n=35 Australia with a population of 23.6
million and n=32 USA for a population of 318 million)
Since this is a very interesting study and has the
opportunity to develop valuable proxy indicators to the
obesogenic food environments, I suggest that the
study should focus on specific geographical areas
(feasible to cover and made representative) and do a
representative sampling of supermarkets and compare
them with local obesity prevalence rates.
were sampled whereas in other areas with greater
diversity in the supermarket sector, multiple chains
were sampled. Auditors were self-selected researchers
interested in the measurement of the within-store
supermarket food environment and sampled from their
cities of residence or other region convenient to them.
Areas sampled should therefore be considered a
convenience sample”
We agree that the sampling methods could be a
potential limitation and have now added the following
paragraph to the discussion section: “A further
limitation of the study is that we cannot be sure that the
supermarkets audited are truly representative of all
supermarkets in each country. This is particularly the
case for England (n=8) where sample sizes were low
both in total and per chain. For some other countries
with considerable diversity in the supermarket retail
sector (Canada, US) the average store size may vary
in different regions. Having said this, sampling in both
of these countries was from multiple cities/regions (two
in Canada, three in the US). For countries where a
larger number of stores from individual chains were
audited (e.g. Australia, the Netherlands, Sweden), the
results are likely to be representative of the store size
of that chain (in each case the leading retailers were
selected). It is worth noting that auditors were asked to
obtain a sample that was representative of the major
supermarkets in their city/region. Given the potential
limitations, the results on store size should be
considered instructive but not necessarily definitive.
Further work to more accurately measure supermarket
store size in different countries would be extremely
useful to confirm our findings.”
See previous comment.
We have addressed the limitation regarding the
representativeness of the sample in the previous
comments from this reviewer. In order to obtain a more
representative sample of supermarkets, a whole new
study would be required. Although we suggest that
further studies confirming our results would be
desirable, we believe that reporting the results from the
current study is nonetheless extremely valuable, as the
reviewer says, to develop proxy indicators for
obesogenic food environments and to stimulate
research in this area.