Cohort studies strengths

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... 

The strengths of observational cohort studies are the depth and quality of data that may be collected. Even though these studies are imstruc-tured in the sense that there are no limiting criteria in respect of patient, drug or dosage, they are defined in size and duration and data collection methods, whether on paper forms or on computer screens, and they can draw the attention of the participating doctor to particular pieces of information that are highly desirable. Should data be deficient or inconsistent then it is a relatively simple matter to go back to the doctor for clarification. 

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. 

Cohort studies measure the strength of an association between an exposure and outcome of interest or disease by comparing the incidence of disease in the exposed population to the incidence of disease in the unexposed population. Absolute measures of association calculate the difference of disease between the exposed and unexposed groups. Excess or attributable risk is the number of extra cases of disease that the exposure is responsible for, assuming that the relationship between exposure and disease is causal. 

The strengths of cohort studies lie in their ability to compute incidence rates and relative risks. They are the best way to examine the incidence and natural history of a disease. Confounding factors are... 

Ruiz JR, Sui X, Lobelo F et al. (2008) Association between muscular strength and mortality in men prospective cohort study. BMJ 337, a439. 

Strength of recommendations A, B, C = good, moderate, and poor evidence to support recommendation, respectively. Quality of evidence 1 = Evidence from >1 properly randomized, controlled trial. 2 = Evidence from >1 well-designed clinical trial with randomization, from cohort or casecontrolled analytic studies from multiple time series, or from dramatic results from uncontrolled experiments 3 = Evidence from opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert communities... 

By the end of the meeting, several panelists recommended that the final toxicological profile address cancer retrospective cohort mortality studies more thoughtfully and that the revised profile portray the strengths and limitations of these studies more accurately. 

Bellinger and Needleman (2003) reanalyzed their earlier cohort data, specifically stratifying the outcomes of the psychometric tests and dose—response strengths for 24-month PbB levels into those <10 pg/dl (N = 48) and those S 10 pg/dl. These authors reported that the dose—response slope, IQ loss versus PbB increase, was threefold steeper at PbB <10 pg/dl than for blood Pb values at 10 units or higher. This curvilinear relationship across the dose—response spectrum at lower versus higher dose has been documented in other individual and aggregated studies noted below. 

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