The use of incentives in vulnerable populations for a telephone survey: a randomized controlled trial.
BACKGROUND
Poor response rates in prevalence surveys can lead to nonresponse bias thereby compromising the validity of prevalence estimates. We conducted a telephone survey of randomly selected households to estimate the prevalence of food allergy in the 10 Canadian provinces between May 2008 and March 2009 (the SCAAALAR study: Surveying Canadians to Assess the Prevalence of Common Food Allergies and Attitudes towards Food LAbeling and Risk). A household response rate of only 34.6% was attained, and those of lower socioeconomic status, lower education and new Canadians were underrepresented. We are now attempting to target these vulnerable populations in the SPAACE study (Surveying the Prevalence of Food Allergy in All Canadian Environments) and are evaluating strategies to increase the response rate. Although the success of incentives to increase response rates has been demonstrated previously, no studies have specifically examined the use of unconditional incentives in these vulnerable populations in a telephone survey. The pilot study will compare response rates between vulnerable Canadian populations receiving and not receiving an incentive.


RESULTS
Randomly selected households were randomly assigned to receive either a $5 incentive or no incentive. The between group differences in response rates and 95% confidence intervals (CIs) were calculated. The response rates for the incentive and non-incentive groups were 36.1% and 28.7% respectively, yielding a between group difference of 7.4% (-0.7%, 15.6%).


CONCLUSIONS
Although the wide CI precludes definitive conclusions, our results suggest that unconditional incentives are effective in vulnerable populations for telephone surveys.
Division of Clinical Epidemiology, Department of Medicine, McGill University Health Centre, Montreal, QC, Canada. megan.knoll@mail.mcgill.ca
Megan
M
Knoll
Lianne
L
Soller
Moshe
M
Ben-Shoshan
Daniel
D
Harrington
Joey
J
Fragapane
Lawrence
L
Joseph
Sebastien
S
La Vieille
Yvan
Y
St-Pierre
Kathi
K
Wilson
Susan
S
Elliott
Ann
A
Clarke
D002170:Canada / Q000453:epidemiology; D005512:Food Hypersensitivity / Q000453:epidemiology*; D006306:Health Surveys; D006801:Humans; D009042:Motivation; D015995:Prevalence; D035862:Vulnerable Populations