Guide for Developing a Cochrane Protocol - Cochrane Public Health ...

If you are including ITS studies we recommend that you assess the risk of bias of these studies
using the EPOC RoB tool for ITS study designs which includes four items from the Cochrane 'Risk
of bias' tool to assess performance, attrition, detection and reporting bias as well as the following
additional items relevant for ITS studies: “was the intervention independent of other changes?”,
“was the shape of the intervention effect pre-specified?” and “was the intervention unlikely to
affect data collection?”.
Both of the EPOC RoB tools mentioned above can be found on the EPOC website:
http://epocoslo.cochrane.org/sites/epocoslo.cochrane.org/files/uploads/Suggested%20risk%20o
f%20bias%20criteria%20for%20EPOC%20reviews.doc as well as guidance for how to prepare a
RoB
table:
http://epocoslo.cochrane.org/sites/epocoslo.cochrane.org/files/uploads/How%20to%20prepare
%20a%20risk%20of%20bias%20table%20for%20reviews%20that%20include%20more%20than%2
0one%20study%20design.doc. Note that for some items in the RoB tool, for example blinding, it
may make sense to provide a different assessment for different outcomes (for example outcome
assessors may be blinded for some outcome measures and not others, or some measures may be
more objective/subjective than others). Where appropriate, add additional items into the RoB
table to allow for this.
Alternative approaches should be discussed and agreed with your contact editor. See Appendix 3
for general information on Risk of bias tables (referenced from the Cochrane Handbook). This is
an area of methodological development and any new tools will be available on the CPHG website.
In this section you also need to describe the method by which you will summarise the risk of bias
assessments. Rather than at the study level, it is recommended that you do this at the outcome
level. This is due to the fact that the risk of bias may be different for different outcomes within
the same study. To do this you can provide an overall risk of bias assessment for the main
outcomes within each study, then provide an overall risk of bias assessment for relevant
outcomes across studies, so that outcomes will be judged overall as ‘Low’, ‘Medium’ or ‘High’ risk
of bias given overall considerations of the study designs, and the potential impact of the
identified risks noted in the table for each study that contributed results for that outcome. Also,
consider how you will address risk of bias in the synthesis of your results, considering how
potential study biases might affect your conclusions.
Measures of treatment effect
In this section you should state how outcomes will be reported (e.g. dichotomous data) and how
you will analyse and compare them (e.g. using Risk Ratios). It is likely that a number of
quantitative outcome measures may be identified. You need to firstly identity the types of data
you will obtain from your included study designs. For controlled studies, with continuous data,
we recommend reporting means or changes in mean scores. Weighted mean difference can also
be reported for continuous outcomes. Standardised mean differences should be reported when
different studies use different scales to report the same outcome (e.g. quality of life scales).
Where a number of outcome measures are identified, authors should use the ratio of means
method (Friedrich 2008). Dichotomous (or binary) outcomes can expressed as relative risks (RR),
odds ratio (OR) or risk difference (RD), however the CPHG recommends using RR (Deeks 2002).
We also recommend using RR for categorical data (e.g. outcomes reported on a short Likert
Last updated: 24 November 2011 - 13 -