The uncertainty (validity and reliability) of three electrothermometers in therapeutic modality research

Context: Data from electrothermometers are used to determine therapeutic modality usage, but the value of experimental results is only as good as the data collected. Objective: To determine the reliability and validity of 3 electrothermometers from 2 manufacturers. Design: A 3 × 4 × 17 factorial with repeated measures on 2 factors. Independent variables were trial (1, 2, 3), thermometer (mercury thermometer, Iso-Thermex calibrated from -50°C to 50°C, Iso-Thermex calibrated from -20°C to 80°C, and Datalogger), and time (17). Setting: Human Performance Research Center. Intervention(s): Eighteen thermocouples were inserted through the wall of a foamed polystyrene cooler, and 6 were connected to each of the 3 electrothermometers. The cooler was positioned on a stir plate and filled with room-temperature water (18.4°C). A mercury thermometer was immersed into the water bath. Measurements of the water bath were taken every 10 seconds for three 3-minute trials. Main Outcome Measure(s): The temperature variability of 3 electrothermometers was taken from a calibrated mercury thermometer. Results: The Iso-Thermex electrothermometers did not differ statistically from each other in uncertainty (validity error ± reliability error = 0.06°C ± 0.03°C ± 0.03°C ± 0.02°C, P < .05), but both differed from the Datalogger (0.64°C ± 0.20°C, P < .05). The Datalogger temperature was consistently higher than the mercury thermometer temperature. Conclusions: The Iso-Thermex electrothermometers were more stable than the Datalogger, and values were within the published uncertainty (±0.1°C) when used with PT-6 thermocouples. The Datalogger we used had an uncertainty of measurement greater than that indicated in the user's manual (∼±0.52°C). Uncertainty of ±0.84°C can significantly influence the interpretation of results when intramuscular temperature changes are usually less than 5°C.