Nested case-control design

The cohort study offers two additional strategies for analysis — case-cohort and nested case-control study designs the case-cohort comprises all individuals in the cohort with a particular disease and a random sample of unaffected individuals from the cohort the nested case-control design includes cohort members with a particular disease (cases) and unaffected individuals (controls) matched on relevant study covariates ... 

Wacholder S (1991) Practical considerations in choosing between the case-cohort and nested case-control designs. Epidemiology, 2 155-158. 

A study of hip fracture risk in relation to the prescription of benzodiazepines exemplifies a nested case-control design. Hip fracture cases and controls were chosen from a large existing database on health care use among Saskatchewan residents. The use of a nested case-control design to assess the role of potential confounding factors efficiently is further illustrated in the previously cited study of inhaled corticosteroids and the risk of fatal and near-fatal asthma. A nested case-control study is an efficient variation of a case-control and a cohort study. In a nested case-control study, all cases (or a sample of all cases) and only a random sample of all controls are chosen for study from the same defined population. 

Supporting evidence for an antiprostate cancer effect of selenium was obtained for a nested case-control design within the Health Professional Follow-up study (Yoshizawa et al. 1998), which found that higher prediagnostic selenium levels were associated with reduced prostate cancer incidence. This study included 33,737 male health professionals aged 40-75 years who provided toenail clippings in 1987. 

High-dose lead exposure is a recognized risk factor for stillbirth or spontaneous abortion. Epidemiologic studies of the impact of low-level lead exposure on reproductive outcome such as low birth weight, preterm delivery, or spontaneous abortion have yielded mixed results. However, a well-designed nested case-control study recently detected an odds ratio for spontaneous abortion of 1.8 (95% Cl 1.1-3.1) for every 5 / g/dL increase in maternal blood lead across an approximate range of 5-20 g/dL (Boija-Aburto et al, 1999). In males, blood lead concentrations in excess of 40 / g/dL have been associated with diminished or aberrant sperm production. 

The biomarker is applied to a population etiological study focused on investigating the role of HCA exposure to cancer. Due to concerns of biases introduced by cancer status ( reverse causation ), a nested case-control study design is preferred. 

Nested case-control study A type of epidemiological research design which investigates the causal association between a risk factor and disease. Both case subjects (people who develop a disease) and control subjects (those who do not develop the disease) are selected from among a defined cohort in which the bio-sample or data of the individuals have been collected at the beginning of the study. Detailed exposure information, such as via the use of biomarkers, is analysed for cases and controls only, not for the entire cohort. The advantages of this design are that it is prospective and is less expensive than the full cohort approach. 

Mexico City pregnant women followed from first trimester (N=668) PbB levels in nested case—control study design Spontaneous abortion rate Odds ratio of 1.8/ 5 pg/dl PbB increase dose—response seen Borja-Aburto etal. (1999)... 

Bradbury et al. (2004), however, recently reanalyzed the relation between tamoxifen and cataracts and described it as a null association, They used a nested, matched, case-control study design and data collected in the General Practice Research Database. They identified all women 30-79 years old who were diagnosed with breast cancer and treated with tamoxifen within 6 months, or with bladder cancer, colorectal cancer, or nonmelanoma skin cancer between January 1991 and December i999. From this population they identified all newly diagnosed cases of cataract and matched four female controls to each case on age, index date, and study entry data. They assessed the risk of cataracts for current, past, and sometime users of tamoxifen... 

A case-control study may be nested within a cohort smdy, i.e. cases and controls are all drawn from a clearly defined cohort. This is an efficient design which is now commonly used in pharmacoepidemiology. Attempts are made in the design and analysis to nimirnise possible biases, and to identify and adjust for confounding factors. Typically a cohort study will measure both absolute and relative risks whereas a case-control study will usually only measure odds ratios which generally approximate to relative risks, hi both cases the data may be summarised in two-by-two tables, as shown in the following examples ... 

What if the designer knows that all case item values are mutually exclusive In such a case, a decoder can be synthesized for a case statement control (the case expression is checked for all possible values of the case item values in parallel) instead of the priority logic (which could potentially be nested deep depending on the number of branches in the case statement). 

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