Results of external validation of clinical prediction rules (CPRs) to rule in or rule out serious infection. aNumber of cases (n) out of the total population of all children (N). bPercentage testing positive in all included children. cIf yes to any of five sequential questions: 1) clinical instinct that something is wrong, 2) dyspnea, 3) temperature greater than 39.5°C, 4) diarrhea, 5) age 15 to 29 months; dDerivation study (italic). e'clinical instinct that something is wrong' replaced by 'clinical impression'. fIf yes to any of the following: 1) shortness of breath, 2) clinicians concern. gIf yes to any of the following: 1) petechiae, 2) nuchal rigidity, 3) coma; probability of illness (in percentage) before testing (blue dot), after a positive test result (red dot with plus to sign) and after a negative test result (green dot with minus to sign).