The aim of this large, prospective, population-wide study was to assess the effect of a financial incentive designed to increase delivery of fluoride varnish to children’s teeth in dental practice in Scotland in line with clinical guidelines. This paper considers, first, change in frequency of FVA pre- and post-introduction of the financial incentive and, second, the potential mechanisms of change through which the incentive may have influenced preventive practice. While introduction of a financial incentive was found to increase FVA rates, the low magnitude of change over time suggests a need for further intervention. Novel use of a validated theoretical framework to understand mechanisms of change suggested that financial incentives operate through complex inter-linked belief systems.
Change in FVA (pre- to post-financial incentive)
Scottish Dental Clinical Effectiveness Programme guidelines advocate the application of fluoride varnish twice a year to the teeth of all children 2 years of age and over (irrespective of caries risk) who attend general dental practice. Yet, even when a fee-per-item payment was made available, dental practitioners’ self-reported FVA rates suggested that only a third apply varnish to the teeth of increased caries risk patients at every visit and less than a fifth to those children assessed as having a standard risk of developing caries. Reported varnish rates were even lower for older children. While this study measured frequency of FVA on an ordinal scale, it would be expected that since most children will not attend practice more than twice a year, practitioners would have to apply varnish at ‘every’ appointment if guidelines are to be met. These findings concur with recent national data showing that in 2015/2016, just 18% of 2–5-year-old children registered with a dentist received two applications of fluoride varnish per year [
47].
Nonetheless, sub-group changes in FVA rates over time demonstrated a pattern commensurate with a positive effect of the financial incentive. The biggest increase in FVA was reported by practitioners who had not worked in a Childsmile pilot practice when considering 2–5-year-old patients, the age group for which a fee was introduced.
While the findings provide some support for growing evidence of the influence of remuneration on healthcare professionals, including dentists’ behaviour [
10,
11,
27‐
29,
48], the low absolute rates of FVA and low magnitude of change over time suggest there is still a need for further intervention to ensure all children in Scotland are getting preventive treatment in line with clinical guidelines.
Mechanisms of the financial incentive
Trends in domain scores over time generally showed a greater positive shift in beliefs which may influence FVA, when those practitioners who had not worked in a Childsmile pilot practice considered their 2–5-year-old patients, than for all other responses. This pattern of results is in keeping with a positive effect of introducing a financial incentive.
After adjusting for time 1 scores in the TDF domains, changes in the novel incentive group (compared to the continuous incentive group) were greater for five domains (knowledge, social/professional role and identity, beliefs about consequences, social influences and emotion). Beliefs related to constructs within these domains may have been influenced by the introduction of the financial incentive during the study period.
The greatest increase in domain scores for the novel (compared to continuous) incentive group was seen for change in the domain social/professional role and identity which measured practitioners’ beliefs that FVA was an important part of their own (or their team’s role). It is plausible that offering a fee-for-service payment for FVA may reinforce practitioners’ beliefs that varnish application was their responsibility. The influence of this domain in predicting dental practitioners’ preventive practice has been previously established [
13,
45] and an association between perceived professional role and the effectiveness of financial rewards found [
49].
Emotion had the second biggest positive difference in domain scores over time for the novel versus continuous incentive groups. This domain was measured by a single item asking practitioners to what extent applying varnish to the teeth of their child patients at least twice a year was something they really wanted to do. Again, it seems intuitive that the introduction of a specific fee for applying varnish may increase practitioner’s agreement with this statement.
Scores in the knowledge domain at time 2 (controlling for time 1) were also found to have a greater positive increase in the novel incentive group. It may be that inclusion of a specific payment for FVA has underscored that applying varnish twice a year is supported by clinical guidelines and/or that introduction of the incentive may have prompted practitioners to further educate themselves in relation to relevant guidelines. Knowledge that varnish is advocated in current guidelines has been found to be associated with varnish application rates [
44].
In light of the financial nature of the intervention and studies highlighting the importance of the domain ‘beliefs about consequences’ [
43,
50‐
52], in influencing professional behaviour, it is unsurprising that change in this domain was also greater in the novel incentive group. However, the difference between groups was not as great as for the domains social/professional role and identity and emotion. This domain measured anticipated consequences for the practitioner, their practice and their patients including perceived financial gain.
The final domain that showed a greater positive increase between time 1 and time 2 for the novel (compared to continuous) incentive group was social influences. This domain measured practitioners’ perceptions of whether their patients and colleagues wanted varnish applied. That decisions to deliver care are influenced by colleagues and patients has been previously demonstrated for a range of professional behaviours including FVA [
43,
45,
50,
51]. The presence of a financial incentive may influence the extent to which FVA is viewed as desired by others. While this finding is difficult to interpret, it may be that the influence of this domain is due to increased collegiate desire of varnish application due to the financial incentive.
Individual analysis of the financial variable representing practitioners’ views of whether they received appropriate financial compensation for applying varnish to their child patient’s teeth were commensurate with a positive effect of the incentive. There was a greater positive change in practitioners’ agreement that they received appropriate compensation (at time 2 accounting for time1 scores) for the novel incentive group.
However, it is worth noting that even when the option of claiming a fee per item for applying varnish was open to them, in general, dental practitioners agreed that FVA would increase in their practice if they were paid more. This suggests that at least some practitioners did not consider the fee sufficient to compensate them. This is in keeping with a qualitative study of Scottish dental practitioners which found that the fee was insufficient to remunerate them for the time involved [
13]. This qualitative study also found that the process of claiming a payment could inhibit FVA. A higher fee may have had a larger impact on the beliefs that influence decision-making and difficulty with the claim system or even perceptions of the difficulty of claiming could have mitigated against a larger intervention effect. Exploring the extent to which the monetary value of the fee and the process for claiming it influenced its effectiveness was beyond the scope of this study.
The importance of considering the appropriate amount of incentive is often raised, although few studies have compared financial incentives of different strengths [
10,
11,
53]. The appropriate amount of financial reward and the likely success of the intervention will depend on the context within which the incentive is operationalised. For example, an interaction between the value placed on a behaviour and incentive strength has been proposed. It may be that a weak incentive to perform a valued behaviour is more effective than a strong incentive to perform a behaviour that is not regarded important [
10]. The financial incentive within this study was operationalised within the context of an engrained restorative culture within dental practice in Scotland.
Overall, the results suggest that financial incentives impact on professional behaviour by influencing complex inter-linked belief systems. In contrast to the sole mechanism being the expectation of direct financial reward, it seems that the introduction of a monetary payment influenced practice through changes to dental practitioners’ wider perceptions relating to the context and culture in which they work. While the mechanisms through which financial incentives change behaviour have been under-theorised and investigated, the findings are in keeping with evidence that incentives operate through indirect belief pathways, for example by normalising or validating the behaviour as part of the professional’s role [
13].
Strengths and limitations
This study has several strengths, not least its scale. Its focus was a population-wide intervention, with explanatory and response variables measured through a census of dental practitioners and their longitudinal follow-up.
The study benefitted from external validity and added to inconclusive literature on the effectiveness of financial incentives as a guideline implementation strategy. While the response rate at time 2 (74%) was very favourable when compared with contemporary surveys of dental practitioners (which achieved returns ranging from 29 to 45%) [
45,
54,
55], just 37% of those originally asked (and who were not known to be ineligible) remained in the cohort. Selection bias cannot therefore be ruled out.
In addition, the national roll-out of the financial incentive precluded a randomised research design. The division of practices at time 1 to Childsmile pilot practices (where dental practitioners could claim a direct fee for varnishing their child patients’ teeth) versus all other practices (with no fee offered) provided a ‘natural’ intervention (novel incentive) and control (continuous incentive) group. However, since these groups had known and possibly unknown differences and secular trends may have influenced the results, caution in attribution and interpretation of outcomes is warranted. While the prospective cohort provides some confidence in the temporality of observed relationships, direct causality could not be inferred.
This study addressed the paucity of literature illuminating mechanisms through which financial incentives operate [
10,
12], importantly through the use of a validated framework. Moreover, while the TDF has been used prospectively to facilitate implementation of health interventions and retrospectively in theory-based process evaluation [
40,
56], its longitudinal use to explore behavioural mechanisms over time was novel. Given that the TDF has proven to be a comprehensive, flexible tool shown to facilitate better understanding of the pathways through which behavioural change occurs [
40,
41,
56], its use was an innovative but appropriate way to further understand how financial incentives operate.
However, although this study added to the evidence that the TDF can be used across different settings and in different ways to better understand the implementation of interventions [
41,
56], the interpretation of results was sometimes difficult. While a quantitative approach was chosen as it facilitated population-wide investigation, with hindsight, a mixed-methods approach incorporating a longitudinal qualitative sub-cohort would have provided further insight into the complex behavioural mechanisms underpinning the intervention.
Additionally, while a priori specification of the behavioural domains likely to act as behavioural mechanism of the financial incentive may have strengthened attributional arguments and may have been possible on the basis of consensus group expertise, a broader exploratory approach (with the exception of initial domain exclusion) was adopted due to the novel nature of utilising the TDF to explain the mechanisms of an intervention longitudinally and lack of robust research evidence specific to the study setting on which to inform hypothesis.
The consensual nature of the TDF approach also merits consideration. Initial domain selection and the selection of narrow items to assess broad domains, although informed by experts, were subjective. Moreover, although internal consistency of domains was high and expert input ensured that measures were specifically relevant to FVA, the allocation of items to domains may elicit theoretical debate [
42].
Finally, the nature of the behavioural measure comprising the main study outcome (FVA) is worth considering. It was not possible to obtain an objective measure of FVA for all dental practitioners at the outset of this study, instead relying on self-report. However, there is no strong basis for the hypothesis that self-report bias would change between time 1 and time 2 or that there would be differential bias (or change in bias) between Childsmile pilot and non-pilot practices.
Further research
There are calls for further robust randomised studies to assess the impact of financial incentives on professional behaviour [
10,
11]. While this is key, in keeping with recent guidance on the evaluation of complex interventions [
57], such studies would benefit from a critical realist perspective combining a focus on rigorous measurement of outcomes with further, qualitative or mixed methods effort, underpinned by theory, to fully understand the mechanisms through which financial incentives work. Quantitative studies using the TDF would benefit from building on, now available, validated measures [
58].
Future studies should consider the strength of the financial incentive, ensure that the claim process does not mitigate against the intervention and consider the context in which the incentive is introduced. It is important to determine the minimal incentive required to effect change in order that policy makers can implement the most cost-effective strategy. Additionally, the introduction of a fee-for-service payment for FVA into the NHS primary care dental contract gives the potential to use an objective measure of FVA in the future.
Finally, further intervention is needed to ensure children in Scotland are getting preventive treatment in line with clinical guidelines. This study and others utilising the time 1 data reported in this paper have gone someway to informing the approach required [
13,
44,
45], but further work is needed to develop and test theoretically informed interventions.