Dey, Michelle

Mohler-Kuo, Meichun

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HINTS & KINKSAn analysis of non-response in a Swiss national surveyMichelle Dey • Meichun Mohler-KuoReceived: 17 February 2012 / Revised: 24 May 2012 / Accepted: 1 June 2012 / Published online: 20 July 2012 Swiss School of Public Health 2012Keywords Response rate  Non-participation Mixed method  SurveyIntroductionSurvey response rates generally have been decreasing overthe recent decades (Curtin et al. 2005; Dillman et al. 2009;Galea and Tracy 2007; Morton et al. 2006). For example,response rates for the annual U.S. National Health Inter-view Survey declined from 80.4 % in 1997 to 72.5 % in2004 and 60.8 % in 2010 (http://www.cdc.gov/nchs/nhis/quest_data_related_1997_forward.htm). The reasonsfor this increasing rate of non-participation could be sum-marized as an overwhelming number of requests for studyparticipation, a general decrease in volunteerism, distrust inscience, and increasing complexity of studies that requirelengthy consent forms or involve complicated procedures(Galea and Tracy 2007 for review).One major concern associated with non-participation isnon-response bias, which refers to systematic errors in datathat occur in a study when the reasons for (non-)partici-pation are somehow linked to the main outcomes of interest(Asch et al. 1997; Curtin et al. 2005; Dillman 1991; Galeaand Tracy 2007). Researchers have tried numerous differ-ent ways to enhance response rates in attempts to minimizenon-response bias and increase the representativeness ofstudy samples. One such means is to utilize a variety ofsurvey data collection methods within a single study(Dillman et al. 2009; Galea and Tracy 2007). With a mixedmethods approach, otherwise eligible individuals who failto respond to one survey method (e.g., telephone inter-views) are subsequently given the opportunity to respondvia another (e.g., written questionnaires). However, prob-lems with mixed method designs may arise when responsesdiffer as a function of the survey method selected (Dillmanet al. 2009; Galea and Tracy 2007).Consequently, the main aims of the present study were(1) to assess whether response rates vary by survey method(telephone vs. mail); (2) to evaluate whether the mainoutcome (in our case, the prevalence of children withspecial health care needs; CSHCN) is influenced by surveymethod; and (3) to identify reasons for non-participation.MethodsThe ‘‘National Survey of Children with Special HealthCare Needs in Switzerland’’ (approved by the EthicsCommittee of the University of Zurich) used a nationalrepresentative sample of 16,496 children, ages 9–14 years,drawn from a canton/municipality-based population(Mohler-Kuo et al. 2011). The main goal of the survey wasto estimate the nationally prevalence of children withspecial health care needs using the ‘‘CSHCN Screener’’with parents as proxy respondents (Bethell et al. 2002). Thesurvey primarily was conducted by computer-assistedtelephone interviews. However, for those parents whosetelephone numbers could not be found (2,859) or whocould not be reached by telephone (1,340), a writtenscreening questionnaire and information letter were sent bymail. On the written questionnaire, the parents were askedto provide their telephone number. If they did, they werecontacted again by telephone. If the parents did not returnM. Dey (&)  M. Mohler-KuoInstitute of Social and Preventive Medicine,University of Zurich, Hirschengraben 84,8001 Zurich, Switzerlande-mail: michelle.dey@uzh.chInt J Public Health (2013) 58:323–326DOI 10.1007/s00038-012-0377-6123the questionnaire within approximately 1 month, a remin-der and second questionnaire were sent. Telephoneinterviews and questionnaires were available in all threeofficial Swiss languages (German, French and Italian). Thereason(s) parents refused to participate could only beassessed among those parents who were contacted bytelephone. Multiple answers were permitted.ResultsAltogether, 10,830 parents (or other caretakers) respondedto the survey (9,371 by telephone interview; 1,044 bywritten questionnaire; 415 by written questionnaire andtelephone interview). The overall response rate was65.7 %. For those parents whose telephone number wasfound and who were reached (12,297), the response ratewas 76.2 % (9,371/12,297). For those parents to whom thewritten questionnaires were sent (parents whose telephonenumbers were not found initially (2,859) and those parentswhose telephone numbers were found but were unable tobe reached (1,340)), the response rate was 34.4 % (1,459/4,199). Hence, those parents who were contacted by mailwere more likely not to participate in the survey(OR = 6.0 (5.6–6.5)). Furthermore, parents of non-Swisschildren were more likely not to participate in the surveyrelative to parents of Swiss children (non-participationrates: 46.2 % vs. 22.8 %; OR = 2.9 (2.6–3.2)). Due to thehigh association between the mode of data collection(telephone vs. written) and nationality (contacted by tele-phone: Swiss parents = 79.2 % vs. non-Swiss parents =57.6 %; v12 = 409.043; p \ 0.001), we included both fac-tors in a logistic regression model to adjust for potentialconfounding. In this model, both factors remained signifi-cantly associated with non-participation. However, theadjusted odds ratio for non-participation declined to 3.6(3.2–4.1) for those parents to whom the questionnaireswere sent and to 2.4 (2.1–2.7) for the parents of non-Swisschildren.Besides looking at response rates, we also assessedwhether actual responses varied as a function of surveymode and found that the prevalence of CSHCN did notdiffer between those who responded by telephone and thosewho responded by mail (13.9 % vs. 13.2 %; v12 = 0.388;p = 0.534).We further examined the reasons for non-participationamong 1,800 parents who actively refused to participate,among whom 79.6 % provided their reason(s) for non-participation (Table 1). The most frequently mentionedreasons for non-participation were ‘‘did not want to provideinformation about their children’’ (23.5 %) and ‘‘lack ofinterest in the study topic’’ (16.2 %). We further examinedthe reasons for non-participation by nationality. Significantdifferences in reasons for non-participation were identifiedbetween parents of Swiss and non-Swiss children. Forexample, versus parents of non-Swiss children, signifi-cantly more parents of Swiss children mentioned (1) ‘‘didnot believe that data protection was ensured’’ (8.1 % vs.1.6 %) and (2) ‘‘lacked trust in the study/research’’ (6.1 %vs. 1.6 %) as their reasons for non-participation. On theother hand, significantly more parents of non-Swiss chil-dren mentioned: ‘‘lack of interest in the study topic’’(23.6 % vs. 15.6 %) and ‘‘were concerned that the inter-view would be overheard by the telephone institutesupervisor’’ (1.6 % vs. 0.3 %) as their reasons for non-participation.DiscussionOur response rate (65.7 %) was similar to that of otherSwiss national surveys (e.g., Swiss Health Survey; BFS2008) and to that of U.S. surveys that have used the sameinstrument (Bethell et al. 2008). The response rate wasmuch lower among those parents who were contacted bymail than those contacted by telephone. However, theresults should be interpreted with caution, because parentswere not randomly assigned to the mail versus telephonesurvey. It is possible that those parents whose telephonenumbers could not be found in the public directory weremore protective of their privacy and, therefore, less likelyto participate in the survey. However, other studies alsohave identified higher response rates with telephone inter-views than mailed surveys (e.g., Wettergren et al. 2011).Furthermore, more telephone numbers were found amongparents of Swiss children than among parents of non-Swisschildren. It is possible that more non-Swiss families choosenot to list their telephone number in the public directoriesor that they just have mobile telephone numbers.The finding that the response rate was higher among theparents of Swiss than non-Swiss children could be attrib-utable to language/comprehension problems. Furthermore,one of the frequently mentioned reasons for non-partici-pation among parents of non-Swiss children was their lackof interest in the study topic that could be partially attrib-uted to language/comprehension problems, because theymight not completely understand the invitation letter thatwe sent them to introduce the study.The finding that the prevalence of CSHCN did not differby data collection mode is indicative of the usefulness ofmixed survey methods: such an approach could be justifiedto increase participation in a study to assess CSHCNwithout introducing bias secondary to data collectionmethod.Lastly, it was demonstrated that a common theme per-colating through several of the main refusal reasons was324 M. Dey, M. Mohler-Kuo123distrust in science (‘‘did not want to provide informationabout their children’’, ‘‘did not believe that data protectionwas ensured’’, ‘‘lacked trust in the study/research’’, ‘‘didnot want to provide information over the telephone’’,‘‘were concerned that the interview would be overheard bythe telephone institute supervisor’’). Despite our efforts toaddress the trust issue, such as giving detailed informationabout the study and assuring all potential-participants aboutdata protection, the problems remained. Other commonreasons for non-participation included: (a) a lack of interestin the study topic (e.g., parents did not feel it was importantto participate in the study when their child was healthy);(b) time constraints (‘‘no time’’, ‘‘considered the interviewtoo long’’); (c) a rising number of study requests promptinga general refusal of all surveys (‘‘felt overwhelmed bytelephone inquires’’, ‘‘did not want to participate in anykind of survey as a matter of principal’’); and (d) personalissues (‘‘felt that the topic was too personal’’, ‘‘personalissues’’).ConclusionsThe present study demonstrates that a mixed surveymethodology approach—combining telephone interviewsand mailed written questionnaires—can be used to increaseparticipation in surveys without influencing studyoutcomes. To enhance survey participation rates in thefuture, it will be especially important to increase the gen-eral population’s overall trust in science (e.g., byadvocating public information campaigns to increase sci-ence knowledge, and providing more detailed studyintroductions including how data will be handled to ensuredata protection). In particular, greater efforts must be madeto encourage and motivate parents of foreign nationalitiesto participate in studies (e.g., by providing additional lan-guage options to reduce non-participation secondary tocomprehension difficulties).Acknowledgments The authors are grateful to Prof. Dr. GuyBodenmann for his extensive input on evaluating the reasons forstudy non-participation, and to Laurent Marti for his valuable input aswell. This work has been supported by the Swiss National ScienceFoundation (325130_125486) and the Swiss School of Public Health.Conflict of interest The authors declare that they have no conflictsof interest.ReferencesAsch DA, Jedrziewski MK, Christakis NA (1997) Response rates tomail surveys published in medical journals. J Clin Epidemiol50:1129–1136Bethell CD, Read D, Stein REK, Blumberg SJ, Wells N, NewacheckPW (2002) Identifying children with special health care needs:Table 1 Reasons for non-participation in the National Survey of Children with Special Health Care Needs in Switzerland (conducted in2010/2011)Total sample(N = 1,800)Parents of Swisschildren (N = 768)Parents of non-Swisschildren (N = 123)v12Did not want to provide information about their children 23.5 % 22.0 % 25.2 % 623Lack of interest in the study topic 16.2 % 15.6 % 23.6 % 4.814*No time 8.0 % 9.8 % 12.2 % 689Felt overwhelmed by telephone inquires 7.3 % 6.5 % 7.3 % 112Felt that the topic was too personal 6.7 % 6.5 % 8.9 % 984Did not believe that data protection was ensured 6.6 % 8.1 % 1.6 % 6.609**Lacked trust in the study/research 5.2 % 6.1 % 1.6 % 4.120*Personal issues 1.5 % 1.3 % 0.8 % 208Did not want to provide information over the telephone 1.3 % 0.8 % 2.4 % 2.914Did not want to participate in any kind of survey as a matterof principal0.7 % 0.8 % 0 % 967Were concerned that the interview would be overheard by thetelephone institute supervisor0.4 % 0.3 % 1.6 % 4.424*Considered the interview too long 0.1 % 0 % 0 % –Other reason(s) 11.8 % 10.8 % 9.8 % 123Reasons for non-participation given by refusing parents reached by telephone (multiple answers permitted). Of the total 1,800 refusing parents,1,433 (79.6 %) provided reasons for their non-participation. Information on nationality was not available for all children; therefore, the Ns ofparents of Swiss or non-Swiss children do not add up to 1,800* p \ 0.05; ** p \ 0.01Non-response in Swiss national survey 325123development and evaluation of a short screening instrument.Ambul Pediatr 2:38–48Bethell CD, Read D, Blumberg SJ, Newacheck PW (2008) What isthe prevalence of children with special health care needs?Toward an understanding of variations in findings and methodsacross three national surveys. Matern Child Health J 12:1–14Bundesamt fu¨r Statistik (BFS) (2008) Erste Ergebnisse der schwe-izerischen Gesundheitsbefragung 2007, Neuchaˆtel, BFSCurtin R, Presser S, Singer E (2005) Changes in telephone surveynonresponse over the past quarter century. Public Opin Q69:87–98Dillman DA (1991) The design and administration of mail surveys.Annu Rev Sociol 17:225–249Dillman DA, Phelps G, Tortora R, Swift K, Kohrell J, Berck J, MesserBL (2009) Response rate and measurement differences in mixed-mode surveys using mail, telephone, interactive voice response(IVR) and the internet. Soc Sci Res 38:3–20Galea S, Tracy M (2007) Participation rates in epidemiologicalstudies. Ann Epidemiol 17:643–653Mohler-Kuo M, Jann B, Dey M, Zellweger U (2011) A recruitmentmethod to obtain community samples of children for surveyresearch in Switzerland. Int J Public Health 56:353–356Morton LM, Cahill J, Hartge P (2006) Reporting participation inepidemiologic studies: a survey of practice. Am J Epidemiol163:197–203Wettergren L, Mattsson E, von Essen L (2011) Mode of administra-tion only has a small effect on data quality and self-reportedhealth status and emotional distress among Swedish adolescentsand young adults. J Clin Nurs 20:1568–1577326 M. Dey, M. 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An analysis of non-response in a Swiss national survey

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An analysis of non-response in a Swiss national survey

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