Table 1 Scale for quality assessment

Representativeness of cases

Selected from cancer registry or multiple cancer center sites

2

Selected from oncology department or cancer institute

1

Selected without clearly defined sampling frame or with extensive inclusion/exclusion criteria

0

Source of controls

Population or community based

2

Both population-based and hospital-based/healthy volunteers/blood donors

1.5

Hospital-based controls without colorectal cancer

1

Cancer-free controls without total description

0.5

Not described

0

Ascertainment of colorectal cancer

Histological or pathological confirmation

2

Diagnosis of colorectal cancer by patient medical record

1

Not described

0

Sample size

>1000

2

200-1000

1

<200

0

Quality control of genotyping methods

Clearly described a different genotyping assay to confirm the data

1

Not described

0

Hardy-Weinberg equilibrium

Hardy-Weinberg equilibrium in controls

1

Hardy-Weinberg disequilibrium in controls

0.5

No checking for Hardy-Weinberg disequilibrium

0