Brief Report - Reducing the Number of Daily Measurements Results in Poor Estimation of Diurnal Variability of Peak Expiratory Flow in Healthy Individuals

AIM: To determine the effect of reducing number of daily measurements on estimation of diurnal variability (DV) of peak expiratory flow (PEF). SUBJECTS AND METHODS: PEF was recorded five times daily for three days in 152 healthy adults. Amplitude percent mean (A%M) and standard deviation percent mean (SD%M) were calculated on third day from five, four, three and two daily readings. Proportion of variability explained by partial schedules was calculated and limits of agreement derived to assess if these methods could be used interchangeably. RESULTS: Four, three and two measurements explained 90-95%, 70-82% and 55% DV respectively using A%M. All schedules of partial measurement using SD%M explained >90% DV. Limits of agreement for A%M and SD%M widened as number of measurements were reduced. CONCLUSIONS: DV obtained by fewer daily measurements agrees poorly with results obtained from five measurements. SD%M is a better alternative if DV is assessed from fewer readings.