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Table 4 Relationship between Number of patients Needed to Screen (NNS) to identify one participant and RCT characteristics

From: The external validity of published randomized controlled trials in primary care

Characteristics Total Trials Median Number Needed to Screen to Identify One Participant (Interquartile Range) P Value
Total 103   
Journal    0.78
BMJ 44 2.95 (1.42–9.30)  
British Journal of General Practice 31 2.30 (1.38–4.42)  
Family Practice 17 1.81 (1.23–3.46)  
Journal of Family Practice 11 2.79 (1.95–7.92)  
Number of enrolees    0.40
<100 40 3.15 (1.63–5.64)  
110–260 31 2.19 (1.22–9.95)  
260–650 15 1.66 (1.32–3.11)  
>650 17 2.78 (1.38–5.16)  
Multicentre    
Multiple 83 2.79 (1.42–6.33)  
Single 16 2.05 (1.18–7.83)  
Unclear 3 1.66 (1.60–5.95)  
Funding Source    0.09
Charity 10 2.61 (1.23–4.48)  
Governing body 3 1.60(1.60–6.06)  
Government 55 2.14 (1.34–6.33)  
Pharma Industry 8 3.98 (2.10–15.59)  
Other 9 5.33 (1.95–7.92)  
Not Listed 18 2.62 (1.23–3.48)  
Intervention Studied    0.47
Counselling/Lifestyle 8 4.75 (2.05–169.71)  
Decision Support aids 6 2.89 (1.42–17.21)  
Educational 21 2.05 (1.34–3.63)  
Pharmaceutical therapy 9 1.89 (1.66–5.16)  
Surgery/procedure 3 1.59 (1.11–9.95)  
Other 55 2.79 (1.42–6.38)