INTRODUCTION
fits, LRTI
LOWER RESPIRATORY TRACT INFECTION, LRTI, COMPLICATION
Lower respiratory tract infection (LRTI) is a frequent trigger for attendance in primary care, where nearly all children are managed, most receiving antibiotics.Judicious and targeted use of antibiotics is likely to be key to both efficient clinical care and minimising the risk of antibiotic resistance. Clinicians are risk averse to a child developing a complication when a prescription has not been issuedHow this fits inTrial data alone can be less useful in generating prognostic models because of the inevitable selection bias (where more unwell children tend to be excluded), but nesting trial data within observational studies increases external validity of analyses and facilitates the generation of more robust clinical prediction models. The current study reports data on the progression of illness from a cohort of children that combines trial and observational data. Both the external validation of an existing prognostic model, and since the performance of the existing model was limited in this cohort of more unwell children, the development of a new internally validated model are reported.