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Relation between socioeconomic status and tumour stage in patients with breast, colorectal, ovarian, and lung cancer: results from four national, population based studies

BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7290.830 (Published 07 April 2001) Cite this as: BMJ 2001;322:830

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Authors response

We are grateful for the opportunity to respond to Professor Bland's
comments on our short report. We deliberately chose the chi-squared test
for heterogeneity because:

(1) this method of analysis permitted comparison with a previous
study;[1]

(2) it allowed inclusion of the unknown category thereby describing
the stage distribution in the whole population, rather than just a
subgroup. In this respect, we therefore disagree with Professor Bland as
we believe it is important to examine the distributions of the missing
data in each deprivation category, particularly as some of these cases
reflected an inability to obtain the appropriate measurement due to their
poor prognoses. As reported in our paper, we conducted tests of
association with and without the unknown categories included in the
analyses; and

(3) we had no reason a priori to assume a linear trend in preference
to non-linear differences, ie that the affluent were distinct from both
the intermediate and deprived (with similar effects) or that the deprived
was the distinct group (with the affluent and intermediate groups having
similar effects).

However, we concede that these reasons are not clear from our paper
because of space limitations. The primary importance of our paper is not
whether a statistically significant trend or association exists, but how
large the magnitude of any potential difference in the stage distribution
might be between the affluent and the deprived. The absolute differences
in stage between the deprivation categories are not large and do not seem
to suggest to us a major problem of presentation with more advanced
disease amongst patients from deprived communities.

David H Brewster

Catherine S Thomson

David J Hole

Roger J Black

[1] Carnon AG, Ssemwogerere A, Lamont DW, Hole DJ, Mallon EA, George
WD, Gillis CR. Relation between socioeconomic deprivation and
pathological prognostic factors in women with breast cancer. BMJ 1994;
309: 1054-1057.

Competing interests: No competing interests

23 April 2001
David H Brewster
Director, Scottish Cancer Registry
Information & Statistics Division, NHSScotland

Trend tests reveal a relationship between deprivation and stage for breast and ovarian cancer

The analyses in this paper do not take into account the ordering of
the categories. The deprivation group is clearly ordered, and many of the
clinical groupings are too, including two of those given for breast cancer
(tumour size and metastatic status) and those for all the others. Thus
the data could have been analysed with a method which takes these
orderings into account, such as the chi-squared test for trend or
Kendall's rank correlation coefficient.

Chi-squared tests for trend yield the following P values: breast
cancer tumour size, 0.02, breast cancer metastatic status, 0.05,
colorectal cancer Dukes' stage, 0.2, ovarian cancer stage, 0.01, lung
cancer clinical stage, 0.02. Subjects for whom stage was unknown have
been omitted. To include `unknown' as a category equivalent to `tumour
size 0-20 mm' is to mix different kinds of category and should not be
done.

Inspection of the table shows that breast cancer, ovarian cancer, and
colorectal cancer tend to be more advanced with worse deprivation
(although not significantly so for colorectal cancer ) and lung cancer
tends to be less advanced. The authors' conclusion that `We found no
consistent evidence that patients from deprived communities present with
more advanced disease for breast, colorectal, ovarian, or lung cancer' may
be true, but only because they did not look very hard. There appears to
be good evidence that patients from deprived communities present with more
advanced disease for breast and ovarian cancer.

Competing interests: No competing interests

10 April 2001
Martin Bland
Prof. of Medical Statistics
St. George's Hospital Medical School
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