To evaluate the difference between chronological and random sequence reading in a series of radiographs with 11 years' follow-up. In addition, the influence of the starting point and length of series was evaluated.
Two experienced readers independently and repeatedly scored digitised radiographs of 62 patients at time points 0, 2, 5, 8 and 11 years of follow-up from the COBRA follow-up database according to the Sharp/van der Heijde method. A linear mixed model was fitted to the data.
Over 11 years the mean scores increased by 3.8 points per year. Compared to random reading, chronological reading resulted in a slightly increased progression rate of 0.4 points per year (p=0.008) and a lower standard error of the mean total progression rate of 0.30 (compared to 0.35 for random reading). Over 11 years, this results in a small difference in progression estimates of about five points, but a highly relevant difference of over 25% of patients needed in a study to find a difference in radiological outcome between two groups. Reading of short series, or series including a baseline radiograph, results in a significantly higher yearly progression rate compared to reading of long series, or series not including a baseline measurement.
Chronological reading of radiographs is preferred above random reading, due to decreased variability around the estimation of the progression rate; this increased efficiency translates into smaller sample sizes, or increased power to detect small differences. For studies with long-term follow-up, the same two readers should read all radiographs, including baseline.