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Assessing the Impact of Non-Response on the Treatment Effect in the Canadian Self-Sufficiency Experiment


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  • Thierry Kamionka
  • Guy Lacroix



In Canada, a policy aiming at helping single parents on social assistance become self-reliant was implemented on an experimental basis. The Self-Sufficiency Entry Effects Demonstration randomly selected a sample of 4 134 single parents who had applied for welfare between January 1994 and March 1995. It turned out only 3 315 took part in the experiment despite a 50% chance of receiving a generous, time-limited, earnings supplement conditional on finding a full-time jobs and leaving income assistance within a year. The purpose of this paper is to determine whether a non-response rate as high as 20% is likely to bias the measurement of the treatment effect. We compare the estimated impact of the program using experimental data only to that obtained using additional data on individuals not taking part in the experiment. We write the likelihood of various sets of information and obtain relevant estimates of program impact on welfare spell durations. We find strong evidence of non-response bias in the data. When we correct for the bias, we find that estimates that rely on experimental data only significantly underestimate the true impact of the program. Au Canada, une politique publique visant à aider les familles monoparentales bénéficiaires de l'aide sociale à s'insérer sur le marché du travail a été mise en place sur une base expérimentale. Ainsi, plus de 4134 chefs de familles monoparentales qui étaient entrés à l'aide sociale entre janvier 1994 et mars 1995 ont été échantillonnés aléatoirement pour faire partie du projet d'Autosuffisance (PAS). Seulement 3315 d'entre eux ont accepté de participer à cette expérimentation alors qu'ils avaient, dans le cadre de l'expérience, 50% de chance de disposer d'un supplément de revenu relativement important mais limité dans le temps. Les personnes qui ont fait partie du groupe de traitement ont pu recevoir ce supplément dès lors qu'elles ont quitté l'aide sociale pour occuper un emploi à temps plein. Dans cet article, nous cherchons à déterminer si un refus de participer à cette expérience de l'ordre de 20% est susceptible d'avoir biaisé l'estimation de l'impact du supplément de revenu. Nous comparons l'effet estimé du traitement en utilisant l'échantillon expérimental seulement avec celui obtenu en utilisant des données additionnelles sur les individus qui ne prennent pas part à l'expérience. Nous écrivons la fonction de vraisemblance et obtenons une estimation de l'impact de ce programme sur la distribution de la durée de séjour à l'aide sociale. Nous mettons en évidence l'existence d'un biais de non-réponse. Nous corrigeons ce biais en tenant compte de la décision de participation et nous montrons que les estimations de l'effet du supplément de revenu obtenues à partir de l'échantillon expérimental seulement sous-estiment de façon importante l'impact du programme.

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Bibliographic Info

Paper provided by CIRANO in its series CIRANO Working Papers with number 2003s-62.

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Date of creation: 01 Oct 2003
Date of revision:
Handle: RePEc:cir:cirwor:2003s-62

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Keywords: Social experiment; non-response bias; duration model; social assistance; Expémentation sociale; biais de non-réponse; modèle de durée; aide-sociale;

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Cited by:
  1. van den Berg, Gerard J. & Lindeboom, Maarten & Dolton, Peter, 2004. "Survey Non-Response and Unemployment Duration," IZA Discussion Papers 1303, Institute for the Study of Labor (IZA).
  2. Cobb-Clark, Deborah A. & Ryan, Chris & Breunig, Robert, 2003. "A Couples-Based Approach to the Problem of Workless Families," IZA Discussion Papers 864, Institute for the Study of Labor (IZA).
  3. Bitler, Marianne P. & Gelbach, Jonah B. & Hoynes, Hilary W., 2008. "Distributional impacts of the Self-Sufficiency Project," Journal of Public Economics, Elsevier, vol. 92(3-4), pages 748-765, April.


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