Methods of measuring asthma severity and influence on patient assignment.
BACKGROUND
There is a need for nonclinical measures in studies where objective clinical data used to determine asthma severity, such as spirometry and peak expiratory flow rate meter readings, are not available.


OBJECTIVE
To determine whether different methods of defining asthma severity provide different distributions of patients across the categories of mild, moderate, and severe asthma.


METHODS
Data were obtained from a mail survey and the database of a managed care organization located in Michigan. Seven methods of asthma severity that used either patient self-report or claims data were evaluated and divided into 3 categories: patient-perceived severity (1 method), symptom-derived severity (4 methods), and medication-derived severity (2 methods). To further evaluate the extent of the degree of agreement among the 7 severity methods, percent agreement and Cohen K scores were calculated.


RESULTS
Surveys were sent to 1,139 persons, and 603 responses were usable. Substantial differences exist in the number of patients in each severity level for different methods of determining asthma severity. The proportion of persons identified as having mild, moderate, and severe asthma ranged from 48% to 82%, 16% to 38%, and 2% to 33%, respectively. The percent agreement and Cohen kappa scores were generally low among the 7 methods.


CONCLUSIONS
Due to variations caused by the method of measuring asthma severity, comparability among studies using different methods of classifying asthma severity is limited. Although a uniform evaluation of asthma severity is needed, the results of this study do not identify one preferable method. Rather, investigators should know the limitations of the methods used.
Lee
Susanna
S
College of Pharmacy, University of Michigan, Ann Arbor, Michigan, USA. run_so_run@yahoo.com
Kirking
Duane M
DM
Erickson
Steven R
SR
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000188:drug therapy / Q000191:economics / Q000453:epidemiology*; D005260:Female; D017048:Health Care Costs; D006801:Humans; D008297:Male; D008824:Michigan / Q000453:epidemiology; D008875:Middle Aged; D012720:Severity of Illness Index; D012737:Sex Factors; D013223:Statistics as Topic; D016896:Treatment Outcome
D018927:Anti-Asthmatic Agents