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EFFECTS ON HEALTH
1992). The relative risk for cardiovascular drugs was 1.3 in the Bonn study and
5.0 in the Erfurt study. The results for other drugs including sleeping pills, sedatives,
tranquillizers and hypnotics ranged between 1.2 and 3.8 in these studies.
All in all, the studies on the relationship between the use of medication or purchase
of drugs and community noise support the general hypothesis of an increase
in sleep disturbance and cardiovascular risk in noise-exposed subjects.
4.5.9 EVALUATION OF STUDIES
This section refers only to studies where the prevalence or the incidence of manifest
cardiovascular diseases was considered as a potential health outcome of
chronic exposure to environmental noise. The focus here is on a quantitative risk
assessment with respect to manifest diseases. Furthermore, studies on the effects
of low-altitude jet-fighter noise are also excluded, because this type of noise
includes other dimensions of stress (for instance, fear). Thirty-seven studies have
assessed the prevalence or incidence of manifest diseases, including hypertension
and IHD (angina pectoris, myocardial infarction, ECG abnormalities).
4.5.9.1 Criteria
Epidemiological reasoning is largely based on the magnitude of effect estimates,
dose–response relationships, consistency of findings, biological plausibility of the
effects and exclusion of possible bias. Internal (the role of chance) and external
validity (absence of bias and confounding) are important issues in the evaluation
of studies (Bradford Hill, 1965). Analytic studies (for example, cohort or casecontrol
studies) are usually considered as having a higher validity and credibility
than descriptive studies (for example, cross-sectional or ecological studies)
(Hennekens and Buring, 1987), although many of the reservations against crosssectional
studies seem to be of minor importance when considering noise. For
example, it does not appear to be very likely that diseased subjects tend to move
differentially more often into exposed areas. Rather the opposite may be true, if
noise stress is recognized as a potential cause of the individual’s health problem.
Thus, a cross-sectional study design may act conservatively on the results. The
presence of a dose–response relationship is not a necessary criterion of causality.
Non-linear relationships, including “u-” or “j-” shaped, saturation and threshold
effects may reflect true associations (Calabrese and Baldwin, 2003; Rockhill,
2005). With respect to the derivation of guideline values in public health policy,
the assessment of a dose–response relationship enables a quantitative risk assessment
on the basis of continuous or semi-continuous (for instance 5 dB(A) categories)
exposure data. Dichotomous exposure data, on the other hand, that refer
to a cut-off criterion which splits the entire exposure range into two halves, can
be used to evaluate the hypothesis of an association (qualitative interpretation),
but not a quantitative assessment. The objective or subjective assessment of exposure
and/or health outcomes is an important issue when judging the validity of a
study (Malmström, Sundquist and Johansson, 1999; Cartwright and Flindell,
2000; Hatfield et al., 2001). The objective prevalence of hypertension was found
to be higher in a population sample than the subjective prevalence of hypertension
(Schulte and Otten, 1993). In a telephone survey more than half of the
hypertensives classified themselves as normotensive (sensitivity 40% for men and
46% for women) (Bowlin et al., 1993). In a representative health survey, the
validity of the self-reported assessment of morbidity (subjective morbidity) was
found to be “low” with respect to hypercholesterolaemia, “intermediate” with
respect to angina pectoris, hypertension and stroke and “high” with respect to
NIGHT NOISE GUIDELINES FOR EUROPE