RT Journal Article
SR Electronic
T1 How many blows really make an FEV1, FVC, or PEFR?
JF Thorax
JO Thorax
FD BMJ Publishing Group Ltd and British Thoracic Society
SP 113
OP 118
DO 10.1136/thx.38.2.113
VO 38
IS 2
A1 M I Ullah
A1 V Cuddihy
A1 K B Saunders
A1 G J Addis
YR 1983
UL http://thorax.bmj.com/content/38/2/113.abstract
AB We have collected peak expiratory flow rates, one-second forced expiratory volumes, and forced vital capacities in sets of 10 or 20 values at one-minute intervals from 30 normal, 49 asthmatic, and 26 bronchitic subjects. Analysis shows that the derivatives are compatible with a normal distribution of the values in the sets, so that the true value is best represented by the arithmetic mean of all valid attempts. One-third of all subjects showed skewness in one or more indices but these were equally divided between positive and negative directions. There is no sign of the dominant negative skewness that would result if the true value was indeed a maximum, which could be approached or equalled but never exceeded. There is no sign that repetition worsens performance. Seventy-two subjects showed no regression in any index and those of the remainder who deteriorated were balanced by equal numbers in all categories who improved. There is a significant tendency for both the highest and the lowest values to occur in the earlier part of any series. Probability theory suggests that this is a statistical phenomenon. The best estimate of the true value of these indices is probably the mean of as many observations as can be conveniently obtained and the data can be treated statistically as if they were a sample from a normally distributed population.