Item 3. Describe the study population: The inclusion and exclusion criteria, setting and locations where data were collected.
Patient population. Female patients attending participating family planning clinics in the states of Washington and Oregon during 1992 and 1993 were considered for enrollment in the study. The previously published screening criteria of the Region X Chlamydia Project were used to establish eligibility for enrollment.[ref] These criteria included any of the following: (i) mucopurulent cervicitis, pelvic inflammatory disease, friable cervix, or abnormal bleeding; (ii) a partner with signs and/or symptoms suggestive of urethritis; (iii) client request; (iv) rape within the previous 60 days; (v) candidacy for intrauterine device insertion; and (vi) a positive pregnancy test and a bimanual pelvic examination. Alternatively, the criteria included two or more of the following: (i) age under 24 years and being sexually active; (ii) new sex partner in the previous 60 days; (iii) sex partner with multiple partners in the previous 30 days; (iv) multiple sex partners in the previous 30 days; and (v) use of nonbarrier birth control method or no birth control method (nonbarrier birth control methods include oral contraceptives, the intrauterine device, sterilization, and all natural family planning methods) 
Since diagnostic accuracy describes the behavior of a test under particular circumstances, a report of the study must also include a helpful description of the targeted population. The eligibility criteria describe the targeted patient population, including additional exclusion criteria used for reasons of safety or feasibility.
Readers must know whether or not the study excluded patients with a specific condition known to adversely affect the way the test works, which would inflate diagnostic accuracy (limited challenge bias). Examples are the exclusion of patients using beta-blockers in studies of exercise electrocardiography and the exclusion of patients with pre-existing pulmonary diseases in studies of ventilation-perfusion scintigraphy.[3,4]
Tests may perform differently in a primary care setting than in a secondary or tertiary care setting. Test performance may differ if the test is used for screening rather than for confirmation of diagnostic suspicion. The spectrum of the target disease as well as the range of other conditions that occur in patients suspected of the target disease can vary from setting to setting, depending on what referral mechanisms were in play.[5,6,7] For these reasons, the report should include a careful description of where patients were recruited and where the test and the reference standard were performed.
|1.||Newhall WJ, Johnson RE, DeLisle S, et al. Head-to-head evaluation of five chlamydia tests relative to a quality-assured culture standard. J Clin Microbiol 1999; 37:681-5.|
|2.||Philbrick JT, Horwitz RI, Feinstein AR. Methodologic problems of exercise testing for coronary artery disease: groups, analysis and bias. Am J Cardiol 1980; 46:807-12.|
|3.||Detrano R, Gianrossi R, Froelicher V. The diagnostic accuracy of the exercise electrocardiogram: a meta-analysis of 22 years of research. Prog Cardiovasc Dis 1989; 32:173-206.|
|4.||Stein PD, Gottschalk A, Henry JW, Shivkumar K. Stratification of patients according to prior cardiopulmonary disease and probability assessment based on the number of mismatched segmental equivalent perfusion defects. Approaches to strengthen the diagnostic value of ventilation/perfusion lung scans in acute pulmonary embolism. Chest 1993; 104:1461-7.|
|5.||Knottnerus JA, Knipschild PG, Sturmans F. Symptoms and selection bias: the influence of selection towards specialist care on the relationship between symptoms and diagnoses. Theor Med 1989;10:67-81.|
|6.||Knottnerus JA, Leffers P. The influence of referral patterns on the characteristics of diagnostic tests. J Clin Epidemiol 1992; 45:1143-54.|
|7.||Melbye H, Straume B. The spectrum of patients strongly influences the usefulness of diagnostic tests for pneumonia. Scand J Prim Health Care 1993; 11:241-6.|