Table 2.

Breakdown of study design characteristics (n = 114 unique primary research articles)

Primary article study design characteristics	n	%
Study design
Cohort	55	48
Case control	27	24
Unclear	32	28
Recruitment criteria
Symptoms and signs	36	32
Other test results	33	29
Referral for index test	7	6
Unclear	37	33
Multiple types within 1 primary article	1	0
Reporting of population characteristics
Age	58	51
Gender	64	56
Distribution of symptoms	76	67
Ethnicity	12	11
Blinded interpretation of test results
Blinded as reported	23	20
Not blinded as reported	20	18
Unclear	70	61
Multiple types within 1 primary article	1	0
Reporting of number of features and training data sample size
Reported	69	57
Not reported	45	42
Verification procedure
Same reference standard	69	61
Differential verification	31	27
Unclear	14	12
Validation
External validation	27	24
Appropriate internal validation	37	33
Inappropriate internal validation	50	44