Data collection and statistical analysis
Each patient chart was scored using the Naranjo scale (Fig 1) and the
Liverpool causality assessment tool (Fig 2). For the questions
addressing whether there has been any objective evidence for the adverse
event, a score of 0 was assigned to all charts since this study aims to
retrospectively assess the tools based only on history and clinical
impression prior to any investigations as a screening method. Charts
scoring “Doubtful” on Naranjo scale and “Unlikely” on Liverpool tool
were considered negative for ADR, and any higher scores were considered
positive for ADR screening. The results of the investigations were
considered as true positive and true negatives. All data was organized
in Microsoft Excel and calculations were done using its algorithm
functions. Positive and negative predictive values as well as the
sensitivity and specificity for Naranjo and Liverpool tools were
calculated using appropriate formulas [20, 21]. The confidence
intervals were determined using McCallum Layton confidence interval
calculator for proportions with confidence level at 95%.