Cross-sectional studies limitations

For styrene, the default intraspecies UF of 10 was reduced to 3 in the calculation of the RfC value, because the lower 95% limit of the exposure extrapolation for a NOAEL in a human cross-sectional study was used and the biologic exposure index had been shown to account for variation in pharmacokinetic and physiologic measures, such as the alveolar ventilation rate (EPA 1993). 

Although the results are not entirely consistent among studies, the evidence on maternal or umbilical cord blood lead (under 10 gg/dL) and the large number of studies led the NTP to conclude that there was sufficient evidence of an association between maternal BLL under 10 gg/dL and reduced fetal growth and low birth weight. In contrast, the NTP concluded that there was only limited evidence that maternal BLL under 10 gg/dL is associated with spontaneous abortion and preterm birth. Although a number of prospective and cross-sectional studies have reported an association between prenatal BLL under 10 gg/dL and preterm birth, the conclusion of limited evidence was based primarily on inconsistency of the data and a large study of mother-infant pairs that failed to find the same relationship. EPA (2012) also concluded that there was little evidence to support an association between maternal or paternal lead exposure and the incidence of spontaneous abortion. 

Data on the incidence and prevalence of occupational dermatoses are scarce. The most important sources of data are occupational disease registries, case series of patients visiting dermatology clinics, and a limited number of cross-sectional studies in one or more occupational groups. There exists a huge amount of data on patch-test patients in different countries (Storrs et al. 1989 Frosch et al. 1993 Schnuch et al. 

Cross-sectional studies of this type can at best show correlations between increased lead-intake and neuropsychological impairment. However, they cannot, or at least only in a very limited way, provide information on the cause-effect-relationships we are concerned with here. A confirmed relationship between increased lead-intake and mental impairment may, in principle, be interpreted to have come about in three ways (Needleman, 1979) ... 

The main objective of any Hearing Conservation Program (HCP) must be the prevention or, at least the limitation of NIHL. After that, the other objectives are the reduction of employees stress and absenteeism, the reduction of workplace accidents as well as workplace quality. The current regulatory levels for occupational noise exposure (European Directive 2003/10/EC and ISO 1999) were based on cross-sectional studies performed a few years ago and before the implementation of hearing conservation programs. 

Althongh population-based cross-sectional studies suggest that air pollution contribntes to human mortality, these studies have severe limitations and have been largely discounted for several reasons. First is the size of the estimated association. If taken literally, these studies suggest that as much as 3-9% of urban mortality in the United States is associated with particulate air pollution. Given that air pollution levels in the United States are relatively low, such a large mortality effect has been considered implausible. 

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