Observer variation in spirometry.
The intra-observer and inter-observer variation associated with clinical spirometry was statistically analyzed. The technical errors for the MEFR and MMF measurements were large enough to question their clinical reliability, especially in borderline instances. Measurement differences between two observers, as in this study, are statistically significant. This observation has special meaning for groups engaged in epidemiologic studies. Significant inter-individual variation will diminish the quality of pooled results.
Chronic respiratory disease among nonsmokers in Hagerstown, Maryland. II. Problems in the estimation of pulmonary function values in epidemiological surveys.
Abstract Prediction equations for the FEV 1.0 and PEFR in a population of white male nonsmokers are presented. Data are also presented to demonstrate the superiority, for epidemiological purposes, of the maximum pulmonary function value in a series of trials over the mean of the sequence. Statistically significant and sizable instrument and interviewer effects were found, and a technique for taking these effects into account is presented. Analysis of published data suggested that the relationship of pulmonary function values to weight, chest expansion and diameter, and hand grip strength should be reinvestigated. Factors influencing the variability of an individual's pulmonary function values are discussed. The importance of these questions to the design and analysis of longitudinal studies of pulmonary function values is emphasized.
A critical discussion of the recorded form of the fast vital capacity record.
Ifanindividual inspires asdeeply ashecanand thenexpires hiswholevital capacity asrapidly as heisableintoarecording spirometer theresultingrecordisknownasa fastvital capacity (F.V.C.) tracing, or,sometimes, asanexpiratory vital spirogram (E.V.S.). Recently muchattention hasbeengiventothepossibility ofusingthis record asa basis fortheprediction ofthemaximum ventilatory capacity (M.V.C.) ofthesame individual, andanumberofpapers haveappeared (RocheandThivollet, 1949;Tiffeneau, Bousser andDrutel, 1949;Gaensler, 1951; Kennedy, 1953) inwhichattempts havebeenmadetocorrelate theslope oftheF.V.C. record-or ofsome portion ofit-with theM.V.C.Kennedy(1953) drawsattention totheformofwhathetermsthe E.V.S. tracing andcommentsthatit isneveruniform throughout itslength, and may,except incertain typesofabnormal patients, bedivided intotwofractions. Thefirst fraction is relatively steep andlinear. Itthenbreaks awayinto asecond fraction, whichisless steep, andlater the curvebecomesundulatory. Theposition ofthe dividing point between thefirst andsecond fraction, i.e., wherethetracing deviates fromastraight line, hasbeentermed thecritical point (Kennedy, 1950)." D'Silva andKazantzis, working inthisdepartment,havelately madeasimilar attempt tocorrelate theslopeoftheF.V.C.record withthe M.V.C.In theirexperience (personal communication) curvesof theform shownby Kennedyareneverrecorded. Theystate thatthe curveisonewitha smoothly changing slope, alwaysconcaveupwards, andthatitdoesnot havethestraight portion followed bya sudden infiexion ata critical pointorthesubsequent region ofsmall undulations (Kazantzis, 1953). Clearly itisa matterofconsiderable importance, bothforthetheoretical implications and forthevalidation ofanypredictions whichareto bemadefromsuchrecords, todecide whichof these verydifferent kindsofcurveiscorrect, and, ifpossible, toexplain thedifferences. E