Sufficiently important difference for common cold: severity reduction.
OBJECTIVE
We undertook a study to estimate the sufficiently important difference (SID) for the common cold. The SID is the smallest benefit that an intervention would require to justify costs and risks.


METHODS
Benefit-harm tradeoff interviews (in-person and telephone) assessed SID in terms of overall severity reduction using evidence-based simple-language scenarios for 4 common cold treatments: vitamin C, the herbal medicine echinacea, zinc lozenges, and the unlicensed antiviral pleconaril.


RESULTS
Response patterns to the 4 scenarios in the telephone and in-person samples were not statistically distinguishable and were merged for most analyses. The scenario based on vitamin C led to a mean SID of 25% (95% confidence interval [CI] 0.23-0.27). For the echinacea-based scenario, mean SID was 32% (95% CI, 0.30-0.34). For the zinc-based scenario, mean SID was 47% (95% CI, 0.43-0.51). The scenario based on preliminary antiviral trials provided a mean SID of 57% (95% CI, 0.53-0.61). Multivariate analyses suggested that (1) between-scenario differences were substantive and reproducible in the 2 samples, (2) presence or severity of illness did not predict SID, and (3) SID was not influenced by age, sex, tobacco use, ethnicity, income, or education. Despite consistencies supporting the model and methods, response patterns were diverse, with wide spreads of individual SID values within and among treatment scenarios.


CONCLUSIONS
Depending on treatment specifics, people want an on-average 25% to 57% reduction in overall illness severity to justify costs and risks of popular cold treatments. Randomized trial evidence does not support benefits this large. This model and these methods should be further developed for use in other disease entities.
Barrett
Bruce
B
Department of Family Medicine, University of Wisconsin, Madison, Wisc 53715, USA. bruce.barrett@fammed.wisc.edu
Harahan
Brian
B
Brown
David
D
Zhang
Zhengjun
Z
Brown
Roger
R
D000293:Adolescent; D000328:Adult; D000368:Aged; D000998:Antiviral Agents / Q000627:therapeutic use; D001205:Ascorbic Acid / Q000627:therapeutic use; D003139:Common Cold / Q000628:therapy*; D020900:Echinacea; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010069:Oxadiazoles / Q000627:therapeutic use; D010080:Oxazoles; D008517:Phytotherapy; D010936:Plant Extracts / Q000627:therapeutic use; D018570:Risk Assessment; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D014815:Vitamins / Q000627:therapeutic use; D017967:Zinc Compounds / Q000627:therapeutic use
D000998:Antiviral Agents; D010069:Oxadiazoles; D010080:Oxazoles; D010936:Plant Extracts; D014815:Vitamins; D017967:Zinc Compounds; C115201:pleconaril; D001205:Ascorbic Acid