MEAN VERSUS MEDIAN FOR THE MULTIPLE SLEEP LATENCY TEST

Since its introduction in the mid-1970s, the multiple sleep latency te st (MSLT) has become the standard method for evaluating hypersomnolenc e. The mean sleep latency is usually calculated and constitutes the tr aditional basis for interpretation. Mean and median are both measures of the central tendency of a distribution, but because the trials of t he MSLT are limited to 20 minutes, the median may be more appropriate. The objective of this study was to compare the value of the mean vers us the median sleep latency in the interpretation of the MSLT. We retr ospectively analyzed 100 MSLTs performed for evaluation of excessive d aytime sleepiness. Patients' ages ranged from 6 to 84 years (mean 43). Mean and median sleep latencies were calculated according to standard formulas. We classified each record into one of three categories, usi ng both the mean and the median sleep latencies: normal (>10 minutes), moderate (greater than or equal to 5 and less than or equal to 10 min utes), and severe sleepiness (<5 minutes). Of the 100 MSLTs, 89 remain ed in the same category (normal, moderate, severe) whether mean or med ian was used. In 11 cases, the category changed. All shifts were by on e category, that is, no shift occurred between normal and severe. This study suggests that, despite valid theoretical arguments for the use of the median, both measures are equally acceptable for clinical purpo ses.