outdoor lighting and crime, part 1 - Astronomical Society of Victoria

crime rate at another time. To investigate this possibility, long time series of
crimes before and after the intervention in experimental and control areas are
needed.”
Only the Bristol study of the British set includes time-series observations. Crime values
were given for nine successive six-month periods but the treatment was staged over 28
months. This study does not meet the usual criteria for a time-series analysis of treatment
effects, eg at least five before time periods.
Farrington and Welsh did not mention the regression to the mean problem in relation to
the US studies. But the likelihood again is that relighting of particular areas was done to try
to control an existing high crime rate, not because the opportunity was available for wellmatched
experimental and control areas for scientific purposes. Unless there is evidence to
show that this confounding effect did not apply or was insignificant, the US results remain
suspect.
If the eight US studies are accepted in the absence of further information, Farrington and
Welsh’s finding of an overall odds ratio of 1.08 for them becomes the result of the metaanalysis.
But the problems do not end there.
Farrington and Welsh cited a reference that the reader has to consult to try to reproduce
the weighting factors used to combine the various estimates of the odds ratio. One should
not have to ‘second guess’ the authors in this way. Explicit details of the weighting factors
or other essential features of the process should have been given so that readers could readily
check the calculations for themselves, and examine the effect of removing one or more of
the studies from the pool used to find the best estimate of the odds ratio. 20
5.5.1 Conflicts of interest issues
The Cochrane Handbook (Clarke and Oxman 2002 [22]) sets out necessary requirements
for acceptable scientific quality of healthcare review articles. It was used as a model for
the Campbell Collaboration (2002) [17] guidelines. In the case of conflict of interest issues,
the two are virtually identical: reviewers should report any conflict of interest capable
of influencing their judgements, including personal, political, academic and other possible
conflicts, as well as financial conflicts. It is hardly surprising that the rules for good science
are consistent across disciplines. Within the healthcare discipline, information about
sources of funding is considered a desirable inclusion in trials reports also (Moher, Schultz
and Altman 2001 [69]).
The Dudley and Stoke-on-Trent papers both acknowledge the managing director of a
lighting company for funding the research. Insofar as the funding provided the means to
do the research and thereby benefitted both authors, and that one of the authors was also an
author of the review, it would seem that these two potential sources of bias should have been
mentioned explicitly in the review, but they were not. Farrington and Petrosino (2001) [33]
suggested a solution to the problem of a review author also being an author of one or more
of the included papers; this is for the review to have an additional author, one who had not
previously worked on the topic. This is understood to be the case for the review and metaanalysis
in question, but halving potential bias does not eliminate it. Under the Collaboration
20 A pair of possible weightings for the UK odds ratio and the US odds ratio can be found from the combined
odds ratio as the roots of a quadratic equation.
42