Table 2

Recruitment intervention and effect on participation

Recruitment intervention^{Reference ID}	Increases	Decreases	Little impact	Inconclusive
Trial design
Open design16 32	●
Placebo* 59		⊙
Patient preference design18			⊙
Zelen design†25		⊙
Internet-based data capture†42		⊙
Obtaining consent
Process—opt-out approach55	⊙
Process—consent to experimental treatment*48 50			●
Process—consent to standard treatment*48 50			●
Process—refuser chooses treatment option*50			⊙
Process—physician modified chance of experimental*48			⊙
Process—participant modified chance of experimental*48			⊙
Form—researcher read aloud56			⊙
Form—altered readability level†19			⊙
Approach to participants
Delivery—video presentation*†28 35			●
Delivery—video presentation plus written information60	⊙
Delivery—audiovisual overview of trials21 22 33			●
Delivery—interactive computer presentation*36 44				●
Delivery—verbal education session45	⊙
Supplementing info—booklet on clinical trials*23 34			●
Supplementing info—study-relevant questionnaire31 37			●
Supplementing info—newspaper article51			⊙
Framing—treatment as faster*52	⊙
Framing—treatment as new*38		⊙
Framing—emphasis on pain or risk*54		⊙
Framing—positively or negatively*43			⊙
Content—more detailed info (inc. total disclosure)*27 53			●
Content—financial disclosure of investigator interest*†57 58		●
Telephone reminders31 49	●
SMS messages26	⊙
Eligibility screening—face-to-face*24 29				●
Eligibility screening—telephone*20	⊙
Eligibility screening—electronic self-complete*29			⊙
Screening personnel46			⊙
Financial incentives
Cash incentive with invitation26	⊙
Paid participation*†17 30	●
Level of trial risk*†17 30				●
Training for recruiters
Training lay advocates†40	⊙
Education sessions†39			⊙
Trial co-ordination
On-site visits†41			⊙
Additional communication†47			⊙

●, Multiple studies; ⊙, single study.
*Includes recruitment to hypothetical trial(s).
†Includes result reported by study authors only (effect size not calculated).