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The uncertainty (validity and reliability) of three electrothermometers in therapeutic modality research
Lisa S Jutte1, Kenneth L Knight, Blaine C Long
1Brigham Young University, Provo, UT, USA. lsjutte@bsu.edu
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 x 4 x 17 factorial with repeated measures on 2 factors. Independent variables were trial (1, 2, 3), thermometer (mercury thermometer, Iso-Thermex calibrated from -50 degrees C to 50 degrees C, Iso-Thermex calibrated from -20 degrees C to 80 degrees 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 degrees 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 degrees C +/- 0.03 degrees C +/- 0.03 degrees C +/- 0.02 degrees C, P < .05), but both differed from the Datalogger (0.64 degrees C +/- 0.20 degrees 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 degrees 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 (approximately +/-0.52 degrees C). Uncertainty of +/-0.84 degrees C can significantly influence the interpretation of results when intramuscular temperature changes are usually less than 5 degrees C.
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