Explanation of how each diagnosis was assigned during the systematic read-through

Spontaneous PTXOccurring with no apparent cause with or without tension
PSP: occurring in otherwise healthy individuals
SSP: occurring in patients with pre-existing lung-disorder
We assigned tension PTX diagnosis if there was evidence in the chart
 both clinically and by chest radiography to support this diagnosis.
Traumatic PTXOccurring as a direct result of trauma, including haemothorax
Iatrogenic PTXOccurring unintentionally as a direct result of treatment, examination or surgery performed on the patient
Perinatal/congenital PTXOccurring in relation to child birth or as a direct result of congenital disorders
Isolated pneumomediastinumTypically occurring after extreme coughing or giving birth
ThoracentesisSurgical puncture and drainage of the thoracic cavity, either diagnostic or as treatment
EmpyemaA condition where pus collects in the pleural cavity
MisclassificationSuspected PTX; however, this was disproved but the diagnosis was maintained and reported to the national database by mistake
No apparent reason for PTXPatients where no apparent reason for their PTX diagnosis was identified, despite thorough examination of all charts from the year 2000 onwards
Probably a PTX incident prior to the year 2000 or possibly misclassification

PTX: Pneumothorax; PSP: primary spontaneous pneumothorax; SSP: secondary spontaneous pneumothorax.