Patients’ and Parents’ Valuation of Fluoride Varnish in the UK and Brazil

Abstract

Objective

This study aimed to elicit WTP values for fluoride varnish application from participants using the publically-funded health services in Brazil and the UK, and aimed to identify differences in the variables impacting these values. A secondary aim was to compare WTP values from parents for their own preventative treatment and their child’s.

Basic research design

Cross sectional analysis of quantitative data collected from participants attending routine dental appointments.

Clinical setting

Clinics hosted by the Pontifical Catholic University of Rio Grande do Sul (PUCRS), Brazil and Newcastle Dental Hospital, UK.

Main outcome measures

WTP for a fluoride varnish application.

Results

The mean WTP for Brazilian adults was R$60.37 (=£15.97). WTP was highly variable and factors affecting it were difficult to identify. UK parents valued fluoride varnish at mean values of £28.21 and £28.12, for themselves and their child respectively. Regression modelling found those with higher incomes had higher WTP in both samples. In the UK, parental and child WTP increased when parents had higher self-perceived need for dental treatment, had experienced recent dental pain, or their child had received restorations in the last 2 years.

Conclusions

WTP for fluoride varnish varied dramatically between individuals. In both countries, it was difficult to predict this variance as factors which would likely impact upon on WTP had a limited effect and were sometimes counter-intuitive. WTP values for a parent and their child did not demonstrate a significant difference.

Introduction

Resources in publically funded health care systems such as the Brazilian Unified Health System (SUS) and the National Health Service (NHS) in the United Kingdom are finite. Decisions regarding resource allocation within these systems can be aided by an understanding of patient preferences. Where patient preferences inform decision making, the result may be a more patient-centred system. Such preferences can also be incorporated in to economic evaluations ³ to inform decision making by policy makers and service managers, such that resources are used efficiently.

The prevention of oral disease is an established aim for dental health care systems worldwide¹⁵. There is substantial evidence for fluoride varnish being effective in the prevention of dental caries¹¹. Increasing the acceptance and provision of preventative care requires changes in behaviour. Determining the factors which influence patient valuation of preventative care may provide the opportunity to increase its uptake. Measures of patient valuation may also contribute to the reorientation of healthcare services through allocation of resources into disease prevention and health protection.

The economic principle of utility can aid the understanding of patient preference and valuation. Utility represents the improvement in well-being from a treatment, and individuals are said to act in a manner which maximises their utility⁷. Therefore, amongst alternative treatments individuals will prefer the treatment which they believe maximises their utility. Utility cannot be measured directly and so is inferred from what an individual is willing to sacrifice to attain the item in question. The willingness to pay (WTP) approach measures the amount of money an individual is willing to sacrifice. Thus, an increased WTP means a greater sacrifice and so a greater preference for the proposed treatment⁴.

WTP is an established economic technique for determining the value that an individual places on an intervention in a hypothetical scenario. It is widely used outside healthcare and has a growing presence in dentistry ^3,12,20.

The aim of this study was to determine the WTP for fluoride varnish in a sample of Brazilian adults as well as parents in the UK. Secondary aims were to compare the factors which influenced WTP values between Brazil and the UK and to compare the differences between WTP for parental prevention and that of their child.

Methods

Setting

This study took place within the context of publically funded dental care in the UK (in Newcastle upon Tyne) and Brazil (in Porto Alegre). In the UK, dentistry is available both under the publically funded NHS (National Health Service) and privately. Similarly, in Brazil dentistry is available under the publically funded SUS (Sistema Unico de Saude) with private options also offered. In the UK, parents of child patients were recruited from the Child Dental Health Department of Newcastle Dental Hospital (NDH). In Brazil, participants were recruited from adult clinics providing primary care services hosted by the Pontifical Catholic University of Rio Grande do Sul (PUCRS).

Intervention

The preventative treatment discussed with participants in this study was fluoride varnish. Patients were informed of the application process as well as the prevented fraction figure of 40%, established in a 2009 Cochrane review¹¹. This was to facilitate a more informed decision regarding their valuation of the treatment.

Sample

In Brazil, inclusion criteria stipulated that the patient was over the age of 18, had the capacity to consent, had at least one natural tooth and utilised the SUS. 100 participants were recruited during August 2014.

In the UK, 100 parents of child patients were recruited to take part in the study in August 2015. The inclusion criteria required the parent to have a child aged between 6 and 16 years, with at least one permanent tooth.

The objective requiring the largest sample size was that which looked at the influence of dental and socio-demographic factors on WTP values. This was analysed using tobit regression models and as such an events per variable (EPV) approach was taken. In this approach a figures of at least 10 EPVs is recommended ¹⁴, equating to 10 participants per variable in the model. Based on this approach, and using an estimate of 10 variables in a model, a sample size of 100 per setting was necessary to satisfy the requirements. Across both settings, the required sample size was therefore 200.

All participants attending the dental clinics and meeting the inclusion criteria were invited to participate. The samples in both settings were recruited on a consecutive basis over a period of 2 weeks in Brazil and 4 months in England.

Questionnaire Design

Information detailing the nature of fluoride varnish, the process of its application and its effectiveness (an evidence-based estimate of the reduction in the risk of requiring a dental restoration expressed as a percentage) was given to patients prior to them completing the questionnaire. This contained questions on demographics, treatment history and self-perceived treatment need, as based on a previous questionnaire for preventative varnish²¹. WTP values were elicited using a bidding card format, see Figure 1. The scenario was developed in conjunction with paediatric dentists in Newcastle upon Tyne, and questionnaires were piloted resulting in minor changes being made to wording. Questionnaires were translated and reverse translated into Portuguese for use in Brazil.

Figure 1. Shows the bidding card given to participants.

Analysis

Analysis was performed using Stata 14.1 (StataCorp LP, Texas USA). As no questions explored participant rationale for a given WTP value all stated values were assumed to correctly describe the WTP and supposed outliers were included. There were no values of zero given and so determination of true and protest zero responses was not necessary¹⁷. None of the data obtained were therefore excluded from analysis. Descriptive statistics detailing the demographic and dental characteristics, as well as the mean WTP values for the samples were obtained. WTP data was analysed using linear regression modelling and tobit regression, to account for left censoring of the data where appropriate. Models were selected using backwards stepwise elimination with r² values used to select best fitting models. Due to non-normal data distribution, a Wilcoxon signed-rank test was completed to compare WTP from UK parents and values given for their child.

Ethical Approval

Approval for this study, in the UK, was secured from Newcastle University’s Faculty of Medical Sciences Ethics Committee (00755/2014) and the West of Scotland Research Ethics Service (15/WS/0132). Approval was obtained in Brazil from PUCRS University School of Dental Science Ethics Committee (0025/14).

Results

Sample

100 adult participants completed questionnaires in each geographical location, giving a total sample of 200. The demographic and dental history data of participants in Porto Alegre and Newcastle upon Tyne are summarised in Table 1. These statistics demonstrate the differences between the two samples, in particular, the Brazilian participants had experienced a greater number of treatments in recent years and claimed a higher self-perceived need for treatment in the next 2 years, with 32% of participants saying it was more than 50% likely that they would need a restoration, compared with the UK participants where only 5% said this.

Table 1. Adult participant demographic and dental variables.

The exchange rate was R$:£ = 3.78:1 ⁸

	Newcastle upon Tyne, England (%) n = 100	Porto Alegre, Brazil (%) n = 100	Total Sample (%) n = 200
Adults
Gender
Male	23	40	31.5
Female	77	60	68.5
Age
18-25	2	22	12
26-40	61	36	48.5
41-50	31	21	26
51-65	6	14	10
66-80	0	7	3.5
Yearly household income (Newcastle upon Tyne)
£0-5199	0
£5200-10399	15
£10400-15599	15
£15600-20799	16
£20800-25999	16
£26000-31199	7
£31200-36399	9
£36400-51999	8
More than £52000	14
Yearly household income (Porto Alegre)
R$0-8688		20
R$8688-17376		35
R$17376-26064		24
R$26064-34752		9
R$34752-43440		7
R$43440-86880		4
More than R$86880		1
Frequency of dental visits
Only when have a problem	21	39	30
Once every few years	1	6	3.5
Once a year	16	10	13
More than once a year	62	45	53.5
Number of restorations in the last 2 years
No fillings	47	49	48
1-2 fillings/crowns	48	35	41.5
3 or more fillings/crowns	5	16	10.5
Perceived likelihood of restoration in the next year
Zero/very low	35	31	33
Less than 50%	36	20	28
About 50%	24	17	20.5
More than 50%	5	32	18.5
Natural teeth remaining
Less than 10	7		7
10-19	16		16
20 or more	77		77
Dental pain experience
Never	28		28
Longer than 2 years ago	45		45
>6 months but < 2 years	13		13
In the last 6 months	10		10
Currently in pain	4		4
Previous fluoride varnish experience
Yes	19	19	19
No	61	68	64.5
Don’t know	20	13	16.5

The dental history data of the children of the parents in the sample from Newcastle upon Tyne is shown in Table 2.

Table 2. Child participants demographic and dental variables.

	Newcastle upon Tyne, England (%) n = 100
Children
Gender
Male	61
Female	39
Age
6-8	40
9-11	36
12-14	19
15-16	5
Cooperation of child to tooth brushing
Very	50
Fairly	43
Not cooperative	7
Frequency of dental visits
Only when have a problem	6
Once every few years	2
Once a year	10
More than once a year	82
Number of restorations in the last 2 years
No fillings	41
1-2 fillings/crowns	38
3 or more fillings/crowns	21
Perceived likelihood of restoration in the next year
Zero/very low	34
Less than 50%	21
About 50%	21
More than 50%	24
Decayed teeth
None	49
1-4	38
5-10	5
More than 10	4
Don’t know	4
Dental pain experience
Never	41
Longer than 2 years ago	7
>6 months but < 2 years	21
In the last 6 months	24
Currently in pain	7
High sugar diet
Yes	32
No	68
Previous fluoride varnish experience
Yes	47
No	44
Don’t know	9

WTP values

The mean WTP for Brazillian adults was R$60.37 (£15.97, £24.43 when adjusted for Purchasing Power Parity¹⁸) with a standard deviation of R$63.44 (£16.78). In the UK, average parental WTP was £28.21 with a standard deviation of £21.33, and average child WTP was £28.12 with a standard deviation of £23.47. The standard deviation of each mean WTP is large, indicating a wide variance in WTP values within the sample. Figure 2 shows the distributions of WTP values in both Brazillian and UK participants, after accounting for Purchasing Power Parity.

Figure 2. Shows the distribution of UK and Brazilian WTP values. Brazilian values have been converted using Purchasing Power Parity.

The range of Brazilian WTP data was R$1-600 (£0.40-242.77 following PPP), with interquartile ranges of Q1 R$30, Q2 R$50, Q3 R$70 – equivalent to £12.14, £20.23, £28.32 respectively following conversions accounting for PPP. In the UK, parental and child ranges of WTP were £1-100, interquartile ranges of the parent WTP values were Q1 £10, Q2 £20, Q3 £40 and in comparison the child WTP values were Q1 £15, Q2 £20, Q3 £40.

A Wilcoxon signed-rank test was completed to compare parent’s own WTP and that for their child in the UK sample. No significant difference was found (p=0.621).

Factors affecting WTP

Tobit regression models indicated that for Brazilian participants, infrequent attendance and a moderate income were significantly positively correlated with higher WTP, see Table 3. Although all dental and demographic variables were considered in model construction, only these variables remained in the model after backwards stepwise elimination. However, most of the variance remained unexplained in the model.

Table 3. Tobit regression models for Brazillian adults, UK parents and their children.

	Coefficient	Standard Error	t	P>t	95% confidence Interval
Brazillian Adults (n=100, r2= 0.0081)
Infrequent attenders (only when they have a problem)	21.21	12.72	1.67	0.099	-4.03	46.44
Moderate income (R$17376-43440 annually)	35.82	12.65	2.83	0.006	10.72	60.93
Constant	37.44	9.84	3.81	0.000	17.92	56.96
UK Adults (n=100, r2= 0.0478)
Parent is a frequent attender	10.40	4.23	2.46	0.016	1.98	18.82
Self-perceived need for treatment >50%	-11.29	4.28	-2.64	0.010	-19.81	-2.77
Parents have had dental pain <2 years	-10.20	4.53	-2.25	0.027	-19.21	-1.20
Child has had dental restorations < 2 years	10.91	4.38	2.49	0.015	2.19	19.63
Parent is female	-12.26	4.70	-2.61	0.011	-21.61	-2.91
Household income > £26,000 annually	10.50	4.19	2.50	0.014	2.16	18.85
Constant	32.09	12.54	2.56	0.012	7.13	57.05
UK Children (n=100, r2= 0.0675)
Self-perceived need for treatment >50%	-12.58	4.59	-2.74	0.008	-21.73	-3.43
Parents have had dental pain <2 years	-10.66	4.82	-2.21	0.030	-20.26	-1.07
Household income > £26,000 annually	15.16	4.54	3.34	0.001	6.12	24.21
Constant	23.23	13.13	1.77	0.081	-2.90	49.37

Tobit regression models were also completed for the UK sample. For WTP for own treatment, these showed there were many variables which significantly correlated with higher WTP. These variables were parents being frequent attenders, a higher self-perceived need for treatment, a recent history of dental pain, having a child with recent restorations, being female and higher income (Table 3). That said, the r² value for this model suggests that it explains little of the variation.

Tobit regression modelling for factors affecting parental WTP for their child’s treatment found significant positive correlations between parental self-perceived high need for treatment, parents having recent dental pain, income and WTP (Table 3). Again, the r² value for this model was very low, with the model once again explaining little of the variation.

An increased parental income correlated with an increased WTP. A variable was constructed to illustrate relative difference of “for self” versus “for child” valuations in the UK sample. A linear regression model was completed to analyse factors affecting this relative difference. The only significant value emerging was that of parental income (p=0.020). This indicates that higher parental income suggests a greater relative WTP difference between a parent’s value and the one stated for their child.

Discussion

This study aimed to elicit WTP values for fluoride varnish application from participants using the publically-funded SUS and NHS, and aimed to identify variables impacting these values. We aimed to compare factors affecting WTP values between adults in the UK and Brazil, and compare WTP values from parents for their own preventative treatment and their child’s.

The findings indicate that prevention of caries is tangibly valued amongst adults in Brazil, but the extent of valuation is exceedingly variable and the variables measured did not affect WTP with the exception of having a moderate income (compared with having either a high or low income) and being an infrequent dental attender which both increased WTP. There were, however, several significant predictors of WTP amongst the UK sample. Interestingly, compared to Brazil, having a high income (versus low or moderate), their child having recently experienced restorations and being a frequent attender resulted in higher WTP values for own fluroide varnish in the UK with the addition of being female and having recent pain resulting in a lower WTP. For WTP for child’s treatment in the UK, having a higher self-perceived need for treatment and having experienced pain recently was related to having a lower WTP with higher income resulting in higher WTP. The difference between parent and child WTP was not significant.

Limitations of the study

Our sample was relatively small (n=200) and not neccesarily representative of either Brazilian or UK populations. However, given the aim was to compare factors affecting WTP rather than absolute WTP values, this is of less concern. In addition, the UK sample consisted only of parents giving rise to limited comparability with the Brazilian sample. Given the modest sample size there is also the possibility that individuals with a significantly aberrant WTP potentially impacted the regression analyses in a manner which resulted in incorrect relationships between factors and WTP being interpreted.

In addition, the WTP method is associated with a number of potential problems. Individuals with a greater ability to pay may exhibit a greater WTP. Usually it is found that the skew introduced by ability to pay is limited ⁴ and the regression results suggest this to be the case here.

Anchoring, starting-point bias and range bias also play a role in introducing inaccuracies in WTP valuations elicited through an iterative bidding format ⁵. As can be seen in the bidding card in Figure 1, the lowest possible WTP values a participant could express a preference for (aside from zero responses) were R$1 and £1 in Brazil and England respectively. Starting at a low figure may have elicited lower WTP values through introduction of cognitive bias towards a lower figure². In addition, at the time of data collection, currency exchange rates made £1 equivalent to R$3.78, making starting bids non-equivalent. Differences in average incomes may further complicate the effects of the different starting values.

In the UK fluoride varnish is applied free of charge in NHS secondary care settings and to those exempt of NHS charges in primary care settings (i.e. those receiving Job Seekers Allowance). We were not aware of whether any participants in the UK population were exempt from charges, and so are unaware of a possible confounding variable which could be evident in our results due to this.

Strengths of the study

The WTP methodology is well-established and, despite some shortcomings discussed earlier, is suited to investigating valuations for interventions in dentistry ^3,12,20. Furthermore, WTP methodology has been used previously in investigations in the context of Brazilian healthcare^9,16. The data collected in this study is novel and of potential benefit in understanding patient preferences for preventative dental interventions in both Brazil and England.

Factors affecting WTP

It is interesting that amongst Brazilian adults, those with moderate incomes were found to have higher WTP values than those with either low or high incomes. It is difficult to say why this is the case, as established socioeconomic gradients in the burden of dental disease would imply that those with the lowest incomes have the greatest to gain from preventative care, and those with the highest incomes the least to gain. Infrequent attenders in Brazil also had higher WTP values. Reasons for this could include unwillingness to return for invasive restorative treatment, perhaps due to fear or inability to attend regular appointments.

Regression modelling revealed some sociodemographic and past dental history variables influenced WTP for both parents and their child in the UK. Previous research in this field has found similar relationships ^1,4,10, though these can be inconsistent and, at times counterintuitive. The commonly found correlation between a higher income and a higher WTP was found once again in this study, though only in our UK sample.

In the UK, parents with a higher self-perceived need for dental care (i.e. over 50% likely to require a restoration in the next year) were WTP less for their own and their child’s preventative care. Possible explanations include participants believing dental caries is an inevitability and doubt regarding the effectiveness of any preventative measures. It is also possible that those with a higher self-perceived need may have more heavily restored dentitions and fear further restorations less. It is plausible that self-perceived need for dental treatment provides a proxy for socioeconomic status which is not accounted for when using income as the determinant of socioeconomic status.

Similarly, Leung and McGrath¹⁰ found individuals with experience of tooth loss had lower WTP values for an implant-borne prosthesis than those with no such experience. In addition, Vermaire et al. ¹⁹ found no significant difference between risk groups (for dental caries) with regards to WTP for preventative dental care and indeed found a lower propensity to attend for preventative treatment amongst those at higher risk. In contrast, Oscarson et al. ¹³ found those at high-risk (as measured by DMFT) to have a higher valuation for preventative care.

Parents stated significantly higher WTP values for own treatment if their child had received any restorations within the last 2 years. Interestingly this did not correlate with higher WTP values for their child’s preventative treatment. It is possible that the child’s need for any invasive dental treatment alerted the parent to the fact that their own dental health may be suboptimal and so their WTP for preventative care increased. Parents who accompanied the child for treatment may also have become more aware of the discomfort and morbidity associated with invasive treatment and they wished to avoid this for themselves.

In comparing the factors affecting WTP between the two countries, it appears that dental experience and self-perceived dental need are only relevant factors in the UK. The reasons behind this are unclear but may be cultural or related to the fact that the sample in the UK were parents. The frequency of attendance appears to operate in different diurections in the two samples and income affects WTP differently in the two countries. Overall, however, neither of the two models predict much of the (extensive) variance and so it is common across both countries that WTP variantion generally remains unpredictable.

Implications of results

As dental and demographic factors appear to be poor predictors of valuation, and can prove to be counterintuitive, the results of this investigation support the notion that each patient should be approached as an individual in both countries, without prior assumptions about their perceptions of preventative interventions. It is incumbent on the dentist and dental care professional to explore the motivations and beliefs behind patient valuations. If prevention can be promoted, and valuations for prevention of oral disease increased, uptake amongst the population may be greater.

Future WTP research with a qualitative component may help to determine motivations behind a chosen WTP. In addition, our results reflect the current difficulties policy makers face when deciding whether fluoride varnish should be offered as a preventative intervention, given its exceedingly variable valuation.

This research emphasises the unpredictability of patient valuations and existing research has already found specific demographic factors to correlate with valuations in an inconsistent manner.

Conclusions

WTP values for fluoride varnish vary dramatically between individuals. It is difficult to explain this variance as factors which would likely impact upon on WTP have a limited effect and are sometimes counter-intuitive. WTP values are similarly unpredictable in the UK and Brazil although dental factors appear to have some influence in the UK but not in Brazil. WTP values for a parent and their child do not demonstrate a significant difference.