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Comparison of Continuous and Discrete Measurements of Dyspnea During Exercise in Patients With COPD and Normal Subjects: Breathlessness

The subjects were told that they could use the entire scale including values between integers.
For the continuous method, the subject adjusted the vertical length of a black bar (0.7 cm wide) on the screen by changing the location of the mouse (in a direction toward or away from the body) to express the perceived level of breathlessness. No verbal cues were given as to when ratings were to be made. The subjects read the following written instructions before performing the exercise test:
This is a scale for rating breathlessness. The No. 0 represents no breathlessness. The No. 10 represents the strongest or greatest breathlessness that you have ever experienced. You should adjust the length of the solid black bar to represent your perceived level of breathlessness by moving the position of the mouse. Use the written descriptions to the right of the numbers to help guide your selection. You should adjust the length of the bar (up or down) at any time during the exercise when you experience a change in your breathlessness. review

Statistical Analysis
Both Linear regression and power function models were applied to relate breathlessness ratings (B) as a function of three X variables: power production (watts), Vo2 (milligrams per kilogram per minute), and Ve (liters per minute).
linear function: B = Ax + b,
where a = slope and b = intercept
power function: B = kX,
where k = constant and = exponent
Linear function and power function values were obtained for each participant at each session at visit 2 and visit 3. Pearson correlation coefficients were calculated to determine the best-fitting linear and power relationships between breathlessness ratings and each of the three X variables. Slopes and x-intercepts of the linear regression equation were compared for the discrete and continuous methods for rating breathlessness at visit 2 and visit 3 using paired t tests.