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Rapid response to:


Does dietary folate intake modify effect of alcohol consumption on breast cancer risk? Prospective cohort study

BMJ 2005; 331 doi: (Published 06 October 2005) Cite this as: BMJ 2005;331:807

Rapid Response:

Should it be encouraged to state the assumptions/inferences on measurements ?

Dear Editor,

It may be suitable to consider the questionaries in this article as
an instrument to measure alcohol consumption and folate consumption.[1]
However there are always assumptions/inferences that need to be made from
what had been measured to what the exposure level really was. In this
case, the subjects’ answers regarding their alcohol and food intake were
used to estimate their alcohol and folate intake amount over a period of
time. Therefore, it would be necessary to infer both the average level of
alcohol intake and folate intake at a time, and the period that the intake
level referred to (at least the length of the period) from the answers on
the questionaries. Based on this assumption, a relationship between the
dose of alcohol intake and folate intake can be further investigated;
otherwise, the relationship being investigated is only about the
relationship between the answers on the questionaries and the incidence of
breast cancer. Similarly in another study on stress and breast cancer,[2]
there was at least an assumption needed to make: the answers given by the
subjects, reflected / strongly associated with the stress level of the
subjects over a period of time (at least length of the time).

Giving clear statements on the assumptions/inference on measurements,
it would be much easier to evaluate the measurement method of a study
based on the information provided in the study, and it would be easier to
further construct a study to test the validity of that particular method.


1. Baglietto, L., et al., Does dietary folate intake modify effect of
alcohol consumption on breast cancer risk? Prospective cohort study. Bmj,

2. Nielsen, N.R., et al., Self reported stress and risk of breast
cancer: prospective cohort study. Bmj, 2005. 331(7516): p. 548.

Competing interests:
None declared

Competing interests: No competing interests

09 October 2005
Wenbin Liang
taking master of public health
Curtin University of Technology