When parents won’t vaccinate their children: a qualitative investigation of australian primary care providers’ experiences
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Increasingly, the experiences and perceptions of parents who decline vaccination are the subject of investigation. However, the experiences of clinicians who encounter these parents in the course of their work has received little academic attention to date. This study aimed to understand the challenges faced and strategies used when general practitioners and immunising nurses encounter parents who choose not to vaccinate their children.
Primary care providers were recruited from regions identified through the Australian Childhood Immunisation Register (ACIR) as having higher than national average rates of registered objection to childhood vaccination. Interviews began with an exploration of provider experiences with parents who accept, are hesitant towards, and who decline vaccination. Participants were asked specifically about how they addressed any difficulties they encountered in their interactions. Thematic analysis focused on encounters with parents – challenges and strategies.
Twenty-six general practitioners (GPs), community and practice nurses (PNs) were interviewed across two regions in NSW, Australia. Providers’ sense of professional identity as health advocates and experts became conflicted in their encounters with vaccine objecting parents. Providers were dissatisfied when such consultations resulted in a ‘therapeutic roadblock’ whereby provider-parent communication came to a standstill. There were mixed views about being asked to sign forms exempting parents from vaccinating their children. These ranged from a belief that completing the forms rewarded parents for non-conformity to seeing it as a positive opportunity for engagement. Three common strategies were employed by providers to navigate through these challenges; 1) to explore and inform, 2) to mobilise clinical rapport and 3) to adopt a general principle to first do no harm to the therapeutic relationship.
Many healthcare providers find consultations with vaccine objecting parents challenging and some, particularly more experienced providers, employ successful strategies to address this. Primary care providers, especially those more junior, could benefit from additional communication guidance to better the outcome and increase the efficiency of their interactions with such parents.
KeywordsVaccination Iimmunisation Communication Vaccine-hesitance Consultation Primary healthcare provider
Australian childhood immunisation register
Local health district
Primary care professionals encounter a variety of challenges in their provision of vaccines to children. These providers must keep up-to-date with increasingly complex vaccination schedules; manage busy clinic schedules; assuage distress about injection pain; and address parental ambivalence about, or even opposition to, vaccination.
While 92% of children living in Australia are fully vaccinated there is a persistent group, estimated at 3.3%, who decline completely, select out or delay vaccinations (vaccine objecting parents). However, these national figures mask regional variations in vaccination objection with some regions recording vaccine objection for up to 14% of resident children [3, 15].
Since 1998, parents or caregivers have been required to demonstrate that their children aged five years or under are fully vaccinated for age, in order to access federal government family assistance payments, and in some jurisdictions, entry to pre-school or kindergarten. Exemptions to this requirement have been available on the grounds of medical contraindication or personal belief. These exemptions were granted if parents provided a form signed by themselves and a vaccination provider (usually a General Practitioner or Registered Nurse). Exemptions on the grounds of personal belief (including religious beliefs), called “Conscientious Objection”, required a provider to declare that they had “explained the benefits and risks associated with vaccination to the parent or guardian…and informed him/her of the dangers of not vaccinating”. This category of exemption was revoked on 31 December 2015.
This qualitative study aimed to explore vaccination providers’ own accounts of consultations with parents who decline some or all vaccinations for their children; the challenges that arise and the strategies providers’ employed to address those challenges. The magnitude of the challenge presented to vaccination providers by parents who decline vaccination for their children, is evidenced by providers’ own observations (admissions) that these consultations frequently degenerate into adversarial encounters, even though they are aware that engaging with parents in this way is almost invariably fruitless .
Nevertheless, primary care providers are known to influence parents’ decisions about their children’s health generally , and exert significant influence on parents’ vaccination decisions, both positively and negatively [4, 5, 6, 19]. Importantly, parents who have reversed a decision to decline vaccination for their children identified ‘information or reassurances’ from a health care professional as the most important driver of this reversal ([14, 23].
The results reported here are a subset of a larger investigation that also sought providers’ feedback on the application of the Vaccination Communication Framework . This study forms part of a multi-study investigation of the perceived vaccination information and communication support needs reported by parents and primary health care providers. The results of this investigation will inform development of a package of communication and information resources and strategies designed to assist health care providers to proactively and positively address vaccine rejection and hesitancy in primary care.
Study design/ approach
Qualitative in-depth interviews were used to explore the experiences and practices of childhood immunisation providers (General Practitioners and Registered Nurses giving immunisations) working in two regions of NSW where Conscientious Objection (CO) exemptions to childhood vaccination are higher than the national average and full vaccine coverage by one year of age is lower. An additional two providers, based outside these areas, and who expressed interest in participating in the research via social media were also interviewed.
Interviews were structured with reference to parental positions described by Leask and colleagues  Although providers’ experiences with parents who accept vaccination were explored, this paper focuses on their experiences with the smallest but most challenging group of parents; those who present as unwilling or not yet ready to vaccinate their children (Selective/Delaying or Declining parents). A brief, thematic interview guide was developed to ensure consistency between interviewers (Appendix). Ethical approval for the study was granted by the Human Research Ethics Committee of the University of Sydney.
Recruitment and sampling
Primary health care providers were recruited to participate in the research using a mixed recruitment strategy, which combined purposive sampling (identifying a population of health care providers likely to encounter parents who decline vaccination) and intensity sampling (including respondents with a particular interest in vaccination).
Using the latest available data recorded for the Australian Childhood Immunisation Register (ACIR), we identified two local health districts (LHDs) in which very low vaccine coverage was observed amongst a single quarterly birth cohort, and in which registered CO exemptions were higher than the national average of 1.77% . One of the LHDs was situated in a rural area and the other in an urban area. Around 83% of children born between the 1st January and the 31st March 2002 living in these areas were fully immunised at age two, compared with 92% nationally. In the rural LHD, CO exemptions had been recorded for 6.5% of the cohort. However, geographically defined sub-groups within this LHD were observed to have recorded exemptions more than four times this rate. CO exemptions in the urban LHD were lower (0.9% overall), ranging between 0.6% and 4.4%.
Practices located within these LHDs were identified and initial contact made by mail addressed to the Practice Manager (in rural area) or email (in the metropolitan area) via the list belonging to the primary care region’s organisational unit, then named a “Medicare Local”.
General Practitioners (GPs), Practice Nurses (PNs) and Community Nurses (CNs) were invited to contact the research team if they were interested in participating in the study. In NSW, 85% immunisations are given by a nurse or doctor in general practice with 12% by public community health clinics . In the rural region, a researcher followed written invitations with face-to-face contact (visits) to offer further information about the study. Providers who expressed interest in participating were then contacted by telephone or email to schedule interview appointments.
Intensity sampling is known to increase access to interesting and divergent responses, broadening the scope of the enquiry, providing richer insights than would otherwise be possible . These cases can also be a source of thematic triangulation. Mixed recruitment strategies, combining purposive intensive sampling, have been used elsewhere [20, 22].
All respondents were interviewed in the initial tranche of interviews. Initial analysis informed a second, purposive round of recruitment, to ensure the range of immunisation provider types were represented. Recruitment ceased when the research team judged thematic saturation had been achieved.
Interviews were conducted in two local government areas between September 2013 and December 2014 in meeting or consultation rooms at various locations convenient to participants. Interviews were conducted by four trained researchers, all of whom had prior experience conducting research interviews and none of whom had prior relationships with the respondents. Digital audio recordings were made and brief supplementary field notes were taken. To preserve fidelity, the senior author trained all interviewers, listened to initial interviews and offered feedback or further instruction as required. Interviewers moderated their data collection strategies by listening to a sample of one another’s audio files, identifying variances, discussing and making minor modifications to their strategies as required.
Interviewers introduced themselves by describing their roles at the university and their interest in vaccination communication research, at recruitment and prior to commencing the interviews. Each participant was interviewed only once and interviews lasted approximately one hour. Participants were offered the opportunity to check their transcripts but none accepted the invitation. Digital audio files were uploaded to a secure server, whereon they were transcribed by a commercial transcription service and deleted from remote devices.
Analysis followed a grounded theory approach [12, 13]. After the first tranche of interviews, transcripts were read and re-read with early codes noted (open coding). Two other researchers independently read a sub-sample of transcripts selected to capture the variation within the sample. A coding workshop was convened to discuss emergent themes and agree on a coding framework. These early themes informed recruitment of respondents for the second tranche of interviews. The second tranche of transcripts was read and the coding scheme was modified slightly to account for further commonalities and variations in participant responses. The data were coded by hand.
In addition, responses given by the two providers who practice outside the target LHDs, were interrogated. This strategy aimed generate insight into the question of whether the accounts given by providers working in low-coverage communities were typical or reflected phenomena shaped by the peculiarities of particular, geographically defined communities.
A total of 26 interviews were completed and analysed. Seventeen participants were GPs and nine were practice or community nurses. There were equal numbers of respondents (n = 13) from the urban and rural LHDs. Seniority and experience varied widely amongst respondents. Six respondents had less than three years’ experience. The remainder had been in their roles for at least three years; some for more than twenty. The majority of providers (24/26) worked in general practices and two worked for community health organizations offering childhood vaccination clinics. All providers who approached the research group in response to recruitment activities were interviewed. The responses given by the two self-recruited providers accorded closely with those offered by providers working in highly vaccine resistant communities.
Our primary finding was that a clinical encounter with a non-vaccinating parent posed significant challenges to healthcare providers and to the provider-parent relationship, which they reported using a variety of strategies to address. In this paper, we explore how declining vaccination was often viewed as conflicting with providers’ professional identities, sometimes seen to generate a communication roadblock, which hampered effective communication with parents and placed the desired clinical outcome in jeopardy. Thereupon we describe a variety of communication strategies providers reported employing to explore and inform parents who decline vaccination for their children, and note their commitment to mobilising clinical rapport as a powerful tool to promote vaccination. Finally, we illustrate providers’ application of the principle, primum non nocere - first, do no harm – to prioritising and protecting therapeutic relationships in the service of child health.
I felt the pressure of the responsibility to the child (GP12)
It just really angers me that there are whole populations of kids here whose kids aren’t protected, because other parents have been irresponsible (GP4)
I think there is quite a strong pushback against medical establishment. So the doctor used to be an authority figure and the doctor used to be someone who could not be questioned (GP14)
They’ll go to the naturopath before they come to the doctor, or they’ll go to the chiropractor before they come to the doctor. Those people will often tell them ‘don’t get vaccinated,’ and so they’ve heard those things from people they trust more than the doctor (GP7)
Signing the vaccination objection form
The issues are in the sense it’s about payment, so that’s the reason why they’ve come. Why should we be drafted in to sign a form that’s actually about payment? Once you’ve got a monetary issue, it’s very hard to have a conversation about (vaccination). So why is it fair for doctors to be asked to do that? It is an ethical dilemma that the government has created (GP6).
If they don’t believe in the system, why should they benefit from the system? (GP14)
I’m happy to sign it, because I think first of all it’s good to engage with (vaccine refusers) and secondly I don’t think they should be discriminated against” (GP1).
They say ‘I know what you’re going to say, I know about the science behind it, I’ve read everything, you’re not going to change my mind, I’m not vaccinating my child’ (GP9)
Every time you come to a brick wall, it gets harder and harder (RN1)
Their answer is ‘no not doing that, see you later’ that’s it. That’s the most difficult, I mean what do you do with that?’ (GP5)
‘If they’re immunised, I breathe this huge sigh of relief, because I just don't have to go there’ (GP6)
Most providers felt it was not possible to have an effective discussion with parents who object to vaccination within a standard 15-min consultation. Many reported that their communication skills were compromised on becoming flustered because they were trying to rush through the parent’s questions and were conscious of their obligation to avoid delaying subsequent patients.
To manage these very challenging consultations with vaccine objecting parents, providers described employing three common strategies: exploring and informing, mobilising clinical rapport and protecting the therapeutic relationship, which was understood to constitute an application of the long-cherished ethical mandate, above all do no harm.
Explore and inform
Respondents described attempting to explore parents’ reasons for vaccine objection and then offering credible information in response. Discussions could be broadly categorized into; 1) concern-based (i.e. countering a specific worry, such as whether vaccines are implicated in the development of autism) 2) risk-based (i.e. whether risk of contracting a VPD or complication is important, risk of travelling with a non-vaccinated child) or 3) knowledge-based (i.e. how the immune system works, benefits of herd-immunity, the practicalities of non-vaccination with regards to childcare/school entry and payments).
Examples of enquiry described by providers for exploring parental vaccine-objection
“Would you mind telling me what in particular you’re worried about?”
“Do you mind if I bring up vaccination at your next visit?”
“How are you feeling …?”
“What would you like to do?”
Respectfully challenging a belief
“That’s interesting, what do you mean by that? ”
You don’t want to cloud the issue. You work out what your major message is and you make sure that's the last thing you say. Because if you give them too much information, the whole brain shuts down (GP16)
Well that's rubbish, you do know that?
… those parents who I cannot persuade with reason, I used to give them a video of children choking and dying of whooping cough, dying of measles, meningitis, dying of diphtheria. Cemeteries full of kids dying of tetanus.
Your little baby who could potentially get a fatal disease is not protected. How would that make you feel?
Providers commonly referred to government-issued resources or their local public health units for information with which to address parents’ concerns. Some described referring to resources with the parent during consultation time or send them home with written information. Less commonly described approaches included examining each specific vaccine ingredient on the vaccine information leaflet with the patient. One spoke of inviting a naturopath into the consultation room to facilitate a balanced discussion.
Mobilising clinical rapport
Rapport is extremely important and I know that when I get someone who’s got some concerns about vaccination, if I can’t establish that therapeutic rapport with them, then it’s going to be difficult (GP5)
I’ll say to them ‘You’re obviously a really great Mum, you really care about your kids’ --- I’ll say something affirming, something positive to the Mum so you let them know that you’re on their side – even though I’m 100% ideologically disagreeing with the decisions they’re making (GP9)
I think the mother honestly just appreciated that, and at some [point] we brought up immunisation and she said ‘well what did you think?’ and I said ‘well I do think it’s really important’. And it seemed as if from that, she said ‘right, okay’.(GP6)
Several clinicians reported re-framing vaccination as being an action consistent with the parent’s strongly held views. For a parent concerned about vaccination as ‘unnatural’, some reported presenting it as a natural stimulator of the immune system. Similarly, some respondents suggested vaccination could be promoted as a socially conscious act and a unique responsibility of a ‘good parent’.
I start off and say ‘look … you don’t have to vaccinate for like that specific vaccination, you can vaccinate around it’. It’s classic - they start vaccinating with one, and then they end up saying ‘look just do it all’. And you end up doing everything (GP2)
They just wanted to pick and mix and you know, we're just going, "Uh really? It's just what you're asking for is too difficult, it's too complicated, it doesn't exist, it's not possible (RN2)
I’d like a bit more information about maybe the middle road, because basically it’s schedule or nothing (GP1)
First, do no harm
I’m reading a lot of the time ‘will you come back and see me or do you just feel bashed? – because I’ve got to create a relationship of some sort so that they’ll still keep coming back. And not just about the immunisation conversation, but about anything (GP6)
So then- then you move into the harm minimisation strategy. So firstly, don’t lose the patient because I think if you become this obnoxious person, "well I'm not going to look after your child if you don’t immunise them", or, "you're a bloody idiot, you know, go and get a life", all you do is you lose the patient and you lose the opportunity to be of some use and some value (GP14)
We found that nurses reported less involvement with vaccine objecting parents, either because consultations with these parents did not reach the vaccinating nurse, or because objecting parents rarely present to nurse-led vaccination clinics.
This study found that most GPs and immunising nurses found discussions with parents who decline to vaccinate their children to be challenging. They felt that these parents cast doubt on their personal and professional integrity, their authority as medical experts and their competence as communicators. These encounters also stimulated strong internal dissonance; many providers felt their professional obligations (to the child and the community) conflicted with the primarily bureaucratic function of exempting parents from complying with the recommended immunisation schedule. Some seemed to resent being called upon to sign the exemption form at all. Some providers managed this dissonance with begrudging acquiescence.
These results are consistent with previous research in Australia and in other countries [17, 20]. One third of American physicians surveyed in 2009 viewed parents’ disagreement with their recommendations as a lack of respect for their medical judgement and experience. Even so, fewer than half of them (15% of respondents) refused to treat children whose parents chose not to vaccinate them . A later survey found 40% of physicians agreed that requests from parents to ‘space out’ children’s vaccinations reduced their job satisfaction .
In adapting to the challenges presented by parents who decline vaccines, some providers reported developing a variety of response patterns. In our study most reported prioritising the therapeutic relationship even in the face of their misgivings about engaging in the exemption process. They believed that doing so would secure future opportunities for engagement and minimise the potential for harm to the child. Sometimes this involved offering an alternative vaccination schedule. Although some respondents expressed an unwillingness to consider diverging from the immunisation schedule.
The practice of prioritising the therapeutic relationship and maintaining parents’ trust is consistent with advice from professional bodies including the Royal Australasian College of Physicians and the American Academy of Pediatrics, which recommends against refusing to treat the children of parents who will not vaccinate their children [8, 18].
The use of engaged exploration to identify parents’ concerns and address them is also consistent with current evidence indicating that parents who are highly hesitant about vaccinating are seeking more balanced information (rather than promotional material) about vaccination that address their specific concerns . While more senior clinicians were more at ease in their encounters with declining parents and more confident in their responses, it is likely they would benefit from opportunities to periodically review and reflect on the effectiveness of their interactions with this group of parents in order to expand their suite of communication tools.
The policy and historical context to this study is relevant. The study occurred during a time of intense national debate about immunisation policy and vaccine objector provisions in Australia at a time when a major newspaper was actively campaigning to remove exemption from childhood vaccination on the grounds of conscientious objection in federal and state legislation . Some opinion leaders in the medical media vocally objected to the form signing process and this joined a generalised chorus of public outrage about parents who choose not to vaccinate their children leading to bipartisan support for an amendment to the incentives legislation.
Some of our respondents appeared to resent being asked to sign parents’ CO forms, viewing this as a civic or bureaucratic function that lay outside their roles as medical professionals; a function that threatened their professional independence and conflicted with their professional obligations to the child and the community. Historically, the medical professions in Australia have been uncomfortable with performing any task that could be or become civil conscription, which is held to be a direct threat to their professional autonomy, and therefore their capacity to act in the interests of their patients. (: 20-23) This position mirrors the principle of the Separation of Powers, which protects the Judiciary (legal professionals) from government interference and has been enshrined in the Constitution of Australia since 1946, when a referendum passed an amendment prohibiting any civil conscription of doctors. Thus, the discomfort expressed by our respondents may reflect a concern that their professional autonomy is under threat from a government policy requiring them to perform an action that may be construed by parents as condoning their decision to decline vaccination for their children.
In November 2015, the Parliament of Australia eliminated the provision for exemption to the requirement that children be fully vaccinated in order for their parents to be eligible for certain financial benefits. While some state governments may continue to require parents who decline vaccination for their children to formally register their objection in order to access childcare, most providers will receive fewer requests from parents to sign their exemption forms. In its place will be new pressure on GPs to provide a medical exemption for previously vaccine objecting parents or to establish complex catch up arrangements in order to comply with federal and state requirements. Hence, the challenge of dealing with parents who choose not to vaccinate their children will remain and most likely intensify for Australian primary care providers. Additionally, our study may provide insights for jurisdictions that continue to require a clinician to sign a personal belief exemption as still occurs in some US states.
This study was limited to 26 healthcare providers, with a higher proportion of GPs compared to nurses participating (17 GPs vs 9 nurses). This may have under-represented the views of nurses. However, as we have suggested, GPs are more likely to have the primary encounter with vaccine-objecting parents. Whilst many providers expressed difficulty with the form signing process, this requirement will be minimised in future interactions as only medical exemption forms will be required to access financial benefits, as both philosophical and religious beliefs will no longer be valid. This study explores providers’ accounts of their behaviour during consultations with parents who decline vaccination for their children. It does not measure or report actual behaviour; neither is it concerned with doing so.
We have identified several common challenges encountered by immunising GPs and nurses during consultations with parents who decline some or all vaccinations. The providers we interviewed were often conflicted about being required to sign Vaccine Objector Forms. Some perceived this task as threatening their efforts to maintain fidelity to their professional obligations to the child and to the community. Some perceived it as a threat to their fidelity to the health of their patient (the child) and the community and a few perceived it as an opportunity to engage parents in a conversation. In Australia and other countries, jurisdictions may involve vaccination providers in bureaucratic processes designed to inform parents or discourage parents from choosing not to vaccinate their children. Although it is often suggested that providers need access to educational materials that address common misunderstandings about the risks and benefits of childhood vaccination, this study suggests that providers also need communication strategies. Such strategies enable them to engender trust and protect therapeutic relationships with parents who decline vaccination. Many experienced providers reported developing these strategies in-situ. Others are likely to welcome further guidance, particularly more junior professionals with less experience in vaccination.
Any system that mandates the interaction of vaccine-declining parents with providers (such as for government payments or school entry) should provide support for those providers. This support may take the form of legal or professional advice; checklists or discussion guides; and/ or decision tools designed to support parents’ decision processes by helping them to consider the implications of their decision in a systematic way. Adequate training in conflict management and specialised communication techniques appropriate to situations of non-adherence should also be made available to vaccination providers.
Understanding providers’ accounts of their own responses to parents who decline vaccination for their children has provided important insights into their communication support needs. Further research will investigate parents’ information and communication needs. Together, these data will inform the development of a suite of communication tools that will be refined and tested.
The authors gratefully acknowledge Sydney North Shore and Beaches Medicare Local who provided financial and practical support for this study and the health professionals in both regions who gave us their time and their stories.
Availability of data and materials
Ethical approval for the conduct of this study was granted subject to the condition that, “All aspects of the study including results will be strictly confidential and only the researchers will have access to information on participants, except as required by law.” Therefore, the dataset supporting the conclusions of this article will only be made available upon request, and subject to approval from the Human Research Ethics Committee of the University of Sydney.
The authors declare that they have each made substantial contribution to the conception and design of the study; acquisition, analysis and interpretation of the data; and/or drafting the manuscript. The authors approve of the version submitted for peer review and accept responsibility for its content. The authors agree to be accountable for all aspects of the work and to ensure that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
The authors declare that they have no competing interests.
Consent for publication
All respondents consented to participate in this research and to have the data they contributed submitted for peer review and publication.
Ethics approval and consent to participate
Ethical approval for the conduct of this study (Project No. 2013/428) was granted by the Human Research Ethics Committee of the University of Sydney. The conditions of this approval included informing potential participants of the risks, benefits and expections associated with taking part in the study, and securing formal consent prior to data collection.
Consultations with parents who decline vaccinations for their children are professionally and personally challenging
Providers develop effective strategies over time, often as a result of unsatisfying experiences
Communication support for providers during these encounters could expedite this learning
- 1.Australian Government Department of Health. ACIR - National Vaccine Objection (Conscientious Objection) Data. Available at: http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/acir-cons-object-hist.htm. 2015. Accessed 10 Apr 2015.
- 2.Australian Government Department of Human Services. Australian childhood immunisation register (ACIR) statistics. Available at: http://www.humanservices.gov.au/corporate/statistical-information-and-data/australian-childhood-immunisation-register-statistics/. 2015. Accessed 10 Apr 2015.
- 7.Cumpston JHL. Health and disease in Australia: a history. Canberra: Australian Government Publishing Service; 1989.Google Scholar
- 10.Editor. Time to stop keepign kids immune from jab. The Sunday Telegraph. Sydney: NewsCorp Australia. 2013Google Scholar
- 12.Glaser BG. Basics of grounded theory analysis. Mill Valley: Sociaology Press; 1992.Google Scholar
- 13.Glaser BG. Grounded theory: 1984-1994. U6 - ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-8&rfr_id=info%3Asid%2Fsummon.serialssolutions.com&rft_val_fmt = info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.title=Grounded+theory&rft.au=Glaser%2C+Barney+G&rft.date=1995-01-01&rft.pub=Sociology+Press&rft.externalDBID=n%2Fa&rft.externalDocID=b24207779¶mdict=en-US U7 - Mill Valley: Book: Sociology Press. 1995.Google Scholar
- 15.Hull BP, Dey A, Menzies RI, et al. Immunisation coverage 2012. Commun Dis Intell. 2014;38:E208–31.Google Scholar
- 17.Kempe A, O’Leary ST, Kennedy A, et al. Physician response to parental requests to spread out the recommended vaccine schedule. Pediatrics. 2015.Google Scholar
- 22.Patton MQ. Qualitative evaluation and research methods. Newbury Park: Sage; 1990.Google Scholar