Cohort studies weaknesses

The two basic types of analytical studies are the cohort and the case-control study. Each has strengths and weaknesses as well as different resource and time requirements. The cohort study involves the study of indi iduals classified by e.xposure characteristics, e.g., a group of welders. The study then follows the development of disease in the welders group as well as in an unexposed comparison population. The measure that assesses the magnitude of... 

Population studies associate tomato consumption with reduced risk to prostate cancer. The most positive associations have come from cohort studies performed before the prostate-specific antigen (PSA)-screening era, and these studies have suggested that the tomato/lycopene effect was the strongest for clinically relevant prostate cancers (Giovannucci 2007). Small human studies have shown in vivo antioxidant effects for tomato products but evidence for lycopene alone is weak (Chen et al. 2001, Porrini and Riso 2000, Riso et al. 2004, Zhao et al. 2006). Animal and tissue culture studies have been... 

Epidemiological studies have different strengths and weaknesses associated with their design (Table 4) shows some of the strengths and weaknesses of the two main methods of prospective cohort studies and retrospective case-control studies. 

The carcinogenicity of 2,3,7,8-TCDD in humans has been assessed in numerous case-control and mortality cohort studies of chemical manufacturing and processing workers and phenoxy herbicide and chlorophenols applicators, Vietnam veterans exposed to Agent Orange, and residents of Seveso, Italy. A major weakness in many of these studies is the lack of adequate exposure data. Exposure levels or... 

A recent meta-analysis examined the association between smoking and the risk of systemic lupus erythematosus in seven case-control and two cohort studies (Costenbader et al., 2004) (Table 12). The combined estimate showed a weak association with current smoking (OR = 1.5), but no association with past smoking (OR = 0.98). 

In addition, five prospective within-population cohort studies have been carried out, four of them on coronary heart disease and one on strokes. The four coronary heart disease studies were carried out in The Netherlands (Zutphen) [139], the USA (Health Professionals study) [140], the U.K. (the Caerphilly study) [141], and Finland [142]. In the Zutphen study, coronary heart disease was inversely associated with flavonol intake, in which a maximum intake of 42 mg/day and a minimum of 12mg/day were recorded. A clear dose-response correlation was observed. In the Health Professionals study, a modest non-significant inverse association was found (flavonoid intake between 40 mg/day and 7 mg/day). The Finnish study indicated a weak inversely associated correlation, while the Caerphilly study involving Welsh men showed that flavonoid intake increased the mortality. 

Recently, the results of three prospective cohort mortality studies have been reported (44,82,83). The design of these cohort studies has addressed weaknesses in the cross-sectional analyses of population statistics. Cohort studies analyze the incidence of health effects in a sample of individuals whose relevant personal characteristics are recorded along with the exposures in question. Measurement of smoking, sex, age, occupation, and other individual characteristics for each participant in the study allow for direct adjustment for hypothesized confounders. 

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