Health literacy profiling in persons with psoriasis – A cluster analysis

Abstract Objective To explore health literacy (HL) profiles within a cohort of people with psoriasis. A cluster approach identifies groups of individuals that have similar HL profiles. The method unmasks sub‐groups with particular HL strengths, or subgroups with limitations, which require tailored healthcare services to improve. Methods A cross‐sectional sample of 792 patients from the Norwegian Climate Helio Therapy Programme in Gran Canaria participated. The HL questionnaire assessed nine HL dimensions. Using Ward's Hierarchical Clustering Method (Stata version 16), we looked for subgroups of patients across the dimensions. We also explored whether these clusters had specific demographic features and associations to outcomes such as psoriasis knowledge, quality of life and self‐management capacity. Result The analysis revealed four unique clusters identifying clinically meaningful subgroups. Two groups stood out as especially interesting. One cluster representing 26.6% of the sample presented severe HL limitations associated with lower psoriasis knowledge, quality of life, self‐management and self‐efficacy. HL domains connected to cooperation with healthcare professionals showed deficient scores. The other cluster included a smaller percentage (7.7%) with high HL compared to the total sample. This cluster was associated with higher self‐management, quality of life and better self‐efficacy. Conclusion The cluster analysis revealed substantial differences in HL profiles within the sample. These results support the importance of a holistic understanding of the HL needs and the vulnerabilities within a psoriasis cohort. Implementing one size fits all approaches, may not be sufficient in psoriasis context to target HL.

Conclusion: The cluster analysis revealed substantial differences in HL profiles within the sample. These results support the importance of a holistic understanding of the HL needs and the vulnerabilities within a psoriasis cohort. Implementing one size fits all approaches, may not be sufficient in psoriasis context to target HL.

What is already known about the topic?
 Health literacy (HL) is an essential factor for ensuring effective self-management of chronic conditions such as psoriasis.  People with psoriasis have lower health literacy scores compared to other chronic conditions.  Holistic care of people with psoriasis requires knowledge about health literacy, selfmanagement support, and management of comorbidities and associated risk factors.

What does this study add?
 There are considerable differences in health literacy profiles within a psoriasis sample; having a low health literacy profile is associated with lower psoriasis knowledge, quality of life, self-efficacy, and self-management.  People in low scoring clusters are not active information seekers, have low social support, and have limited faith in building relationships with health care providers.  Our findings suggest that knowing health literacy profiles can guide the development of tailored health literacy interventions, securing high utility and uptake in the psoriasis context. Still, several critical knowledge gaps remain, and many patients lack an efficient treatment regime 1, 2 . One such knowledge gap is related to profiling the ability of patients to make use of health information related to psoriasis, named health literacy.
Health literacy (HL) refers to a person's ability to engage effectively with health information and services 3 and is a multidimensional concept covering functional, social, and critical dimensions 4 . Poor HL creates barriers to understand one's health, illness, and treatment fully.
In the health literacy field, most of the research has been focusing on reading comprehension and numeracy skills, better known as "functional" HL 5 . However, measuring only functional HL overlooks the complexity of cultural and personal values, the importance of context, and the social resources and individual motivation that influence peoples` ability to understand and act upon information associated with their health 6 Previous findings from this sample 7 showed that the participants with psoriasis generally scored low on most of the HL domains, also compared to people with other chronic conditions [8][9][10] . However, these results provided only information of the whole sample, and the linear regression models gave no indications to whether there were significant HL differences within the psoriasis cohort. To be able to examine the Health Literacy Questionnaire (HLQ) data 10 and reveal possible subgroups of participants, to use latent profiles or cluster analysis (CA) is recommended 11 . Conceptually, CA aims to identify cluster solutions that are relatively homogeneous within each group, leading to clusters that show high intra-class similarity, while maximizing heterogeneity between the groups, leading to low inter-class similarity across the clusters 12 . Hence, this study aimed to provide detailed profiles of HL strengths and weaknesses in the psoriasis cohort. The following research question is asked:

Patients and methods
A total of 792 participants > 18 years (65% response rate) provided sufficient data to be included in the cluster analysis. They had previously (once or several times from 2011 to 2017) participated in the Norwegian Climate Heliotherapy (CHT) program in Gran Canaria.
They were by postal mail requested to partake, and a reminder letter was sent after six weeks.
Data collection took place from March to August 2017.

The Climate Therapy Program (CHT)
Climate therapy/heliotherapy (CHT) comprises sunlight and saltwater treatment to relieve symptoms and is one of the therapeutic options available to Norwegian patients with moderate to severe psoriasis. CHT is provided in the Canary Islands (located in the Atlantic Ocean at 28°N, 16°W) and includes three weeks of individualized sun exposure in increasing doses as the primary treatment. Additionally, the program emphasizes daily physical training, tailored education, group discussions, individual consultations, and nurse and dermatologist supervision (Aim and content of the CHT see Supplementary file1). Previous studies have reported that CHT has positive effects on outcomes such as; disease severity 13,14,15,16 , mental health 17 , level of knowledge 18 , self-management 15 and health-related quality of life 16 .

Ethics
The study was approved by the Regional Committee for Medical Research Ethics for Southern Norway (ID 2016/1745) and conducted following the Helsinki declaration.

Measures
Socio-demographics included age, gender, education, marital status, years with psoriasis, and the number of other diseases.
The Health Literacy Questionnaire (HLQ) 10 includes 44 items over nine independent scales.
Each scale represents a different element of the overall HL construct. The opening five scales comprise items that ask the respondents to indicate their level of agreement (scoring 1 to 4), and the remaining scales (6-9) embody ranges of self-reported capability (scoring 1to 5). A lower score indicates a lower HL. The full HLQ offers nine individual scores based on an average of the items within each of the nine scales, with higher scores indicating higher health literacy. The Self-Administrated Psoriasis Area and Severity Index (SAPASI) 19 measures disease severity, a structured instrument that allows subjects to assess accurately the severity of their psoriasis (score 0-72, where a higher score indicates more severe disease).
An adapted and simplified version of the Self-Administered Comorbidity Questionnaire (SCQ-18) measured medical comorbidity, where higher scores indicate a more severe comorbidity profile 20 .
Two scales ("Skill and technique acquisition" and "Self-Monitoring and insight") from the Health Education Impact Questionnaire (HeiQ) measured self-management 21 . The scale scores range between one and four. A higher score indicates better self-management.
The General Self-efficacy (GSES) scale measured self-efficacy 22 The scale has ten items with a response range from 1 (not at all true) to 4 (exactly true), and a higher score means higher self-efficacy.

Statistical analysis
Descriptive statistics report the characteristics of the study population. The expectationmaximization (EM) algorithm was used to impute missing HLQ item scores as previously employed by Beauchamp et al. 9 . For all HLQ scales, assumptions of normal distribution were met.
Using Ward's method, the cluster analysis was performed in Stata version 16 to identify and group participants with similar profiles of HL scores across the nine HLQ domains 25 Hierarchical Clustering Method measures cluster adequacy by evaluating distances between cluster centroids (a measure of cohesion) and different distances produce different cluster solutions 26 . The clusters are presented as means (SD) for each domain score in each cluster and accompanied by information about socio-demographic distributions across the clusters.
The method for choosing the number of clusters is guided by seeking to minimize the remaining variance within each scale within each cluster, as presented in earlier HLQ research 27 . For example, if standard deviations (SD) are greater than 0.6 for one or more of the scales, it may indicate that there is still significant subgroups within the cluster and ensuring that clusters represent different patterns of needs and strengths across the nine HLQ domains.
Following the cluster analysis, a regression analysis was performed investigating each clusters` socio-demographic profile and significant associations. The variables entered into the equations as independent variables were based on the arguments of factors associated with psoriasis or other chronic conditions and health literacy from preceding research (i.e. introduction). The choice of using the two-step multiple regression analyses were done to see if variables were separately associated by socio-demographic or with clinical variables.
The following two steps were performed with regard to entering independent variables into the regression analysis: Step 1: Age, gender and high education as independent variables Step 2: Step1 + heiQ domains (self-management), Psoriasis knowledge (PKQ), number of diseases, SAPASI (psoriasis severity), self-efficacy and quality of life (DLQI) as independent variables.

Socio-demographic and clinical characteristics:
The participants had a mean age of 53.2 (SD 12.3) years, 47.5% were female, and they had a mean duration of psoriasis of 28 (SD 14.6) years ranging from one to 77 years ( Table 2).

Clusters of health literacy with socio-demographic profiles and significant associations
In this sample, four clusters were chosen as the optimal cluster solution, based on cluster size and HL pattern diversity 27 . These profiles ranged from people with lower HL who may require ongoing support to manage their health, through to people with higher HL who were more self-confident users of health information and services. See Table 2 for more information on socio-demographic characteristics and descriptive statistics. Table 3 presents mean HLQ scale scores of the total population with Cronbach Alpha values. Each cluster presented a unique HLQ subscale pattern, also shown in Table 4 and Figure 1.   higher education. They had a mean score of 24.6 (SD 7.1) in psoriasis knowledge and a score of 43.8 (SD 9.9) in the BIPQ. The regression analysis shows that lower self-monitoring and insight (st.β -.160) related to self-management is significantly associated with this cluster.
Here, the variance explained by the model (adjusted R-square) was 2%.   Doing the cluster analysis provided a clearer picture of the particular HL subgroups and certified our ability to confirm their liability and further describe their specific challenges. For example, cluster 1, representing 26.6 % of the sample, showed severe HL limitations that were associated with lower psoriasis knowledge, lower quality of life, self-management and self-efficacy. HL domains connected to cooperation with HCPs showed especially low scores.
This means that these patients lack support from HCP as well as their social system 10  Our analysis found that patients in the four subgroups also differed significantly concerning their associations to demographics and other relevant outcomes, and we found a strong predisposition towards poor health indicators in clusters with insufficient HL profiles. In general, there is a definite trend towards more adverse health outcomes in the clusters with many health literacy challenges. The cluster with the most inferior HLQ profile (cluster 1) also showed significant negative associations to self-management, psoriasis knowledge and quality of life. Also, in the study with chronic renal failure patients, the subgroup with the lowest HL profile scored significantly lower on quality of life compared to the mid-level and high-level clusters 28 . In this cluster, we also found a lack of ability to engage with HCPs, to navigate the health care system, and with getting help from their social environment, indicating a need for increased initiative and support by the HCPs 30 . However, the cluster 1 group, scored somewhat better in the actively managing my life domain. Maybe this is caused by a need to compensate for the lack of other support, being forced to take responsibility for their health and make their own health-related decisions 10 .
The framework of HLQ 10 and other studies 9, 31 has established that patients in each cluster should have at least some strengths, but also report limitations on other HL dimensions. There seems to be limited research on health literacy in other chronic, pruritic dermatoses, such as atopic eczema, nodular prurigo or lichen planus. One Korean study 37 found that middle school children with atopic dermatitis had significantly lower e-health literacy than those without the disease. A small study exploring HL in patients with epidermolysis bullosa 38 found that 57.6% had inadequate health literacy in reading skills. There has been some research related to HL in education materials 39 , but otherwise, there seems to be a novel research field to explore health literacy and important associations within chronic dermatological diseases.
This study has some limitations. We do not know whether the population participating in CHT are comparable to the Norwegian psoriasis cohort. The non-responders of our study may mostly be CHT participants not responding positively to climate therapy. Due to lack of ethical consent for non-responders, we did not obtain data about this group.It is possible that we overestimate the level of HL in our sample due to the self-report nature of the data collection, as people with very low HL may not participate in such a survey. Even if the survey does include satisfactory variations in demographic and clinical characteristics (Table   2), the participants are to a great deal middle-aged, even if their ages range from 21-83. In addition, the cross-sectional design makes any causal conclusions impossible.
We did not find statistically significant associations between any of the clusters and gender, education, comorbidity, SAPASI, or illness perception. It is well known that psoriasis and depression amplify each other 40 , and studies in other chronic conditions have shown that depression negatively correlates with health literacy 41 . A limitation of this study is our inability to check whether HL correlates with depression or anxiety in this psoriasis cohort..
For example, a Slovakian study 42 exploring whether depression and anxiety mediate HL's association with diet non-adherence in dialyzed patients found that patients in the low and moderate HL groups were more likely to report both anxiety and depression. Hence, increased levels of depression and anxiety in patients with limited HL may reduce their capacities to find, understand, and act upon health information even more, leading to less effective selfmanagement. Further studies seem needed to determine the connection between anxiety and depression levels and health literacy and examine the exact extent of HL needs on selfmanagement for patients with psoriasis.

Conclusions
The health literacy profiles have provided a thorough assessment of the context-specific needs and HL challenges among people with psoriasis having participated in climate therapy. While some subgroups might have a similar "total score," the actions for improving their outcomes