Table 3.

Possible explanations for the variability noted among published studies of screening mammography

Characteristics of the population screened

• Age (e.g., percentage of women <50 years of age)

• Initial versus subsequent screening examination

• Presence of risk factors for breast cancer

• Presence of breast symptoms

• Self-referral versus physician referral

Features of the mammography examination

• Equipment type and year

• One or two views of each breast

• Single or double readings

• Technician training

Features of physicians interpreting the mammogram

• Experience of the physician

• Level of personal comfort with ambiguity

• Individual thresholds to label film as abnormal

Features of the health care system

• Malpractice concerns

• Financial incentives

• Private versus academic/public programs

• Different stated goals for the percentage of mammograms judged      abnormal and positive predictive value

• Quality control and auditing procedures

• Variability of definitions used to calculate outcomes