Validity and Reliability of the Foot Care Scale for Older Diabetics in Turkish Society

Diabetes is a chronic metabolic disorder, and the number of patients diagnosed with diabetes has grown in recent decades.¹ The main purpose of the management of diabetes is to prevent complications.²

Diabetic foot ulcers are an important complication of diabetes and affect 4% to 10% of patients with diabetes.³ Consequences of diabetic foot ulcers include increased mortality risk, hospital length of stay, and cost, as well as decreased quality of life and a significant risk for extremity loss.⁴ These wounds affect patient activities of daily living and instrumental activities of daily living. Of note, diabetic foot ulcers are the leading cause of nontraumatic lower extremity amputations.^5,6

Foot care is the main intervention to prevent diabetic foot ulcers. For this reason, it is important to improve foot care self-management in patients with diabetes.⁷ Chellan et al (2012) reported that there was an inverse relationship between diabetic foot ulcers and foot care knowledge and practice.⁸. For this reason, assessment of the patient’s foot care self-management ability is a major component of strategies to prevent diabetic foot ulcers.⁷

In Turkish society, 4 tools are reported to be valid and reliable for assessing foot care knowledge and practice: the Diabetic Foot Care Self-Efficacy Scale (DFCSES),⁹ Diabetes Foot Self-Care Behavior Scale,¹⁰ Foot Self-Care Behavior Scale (FSCBS),¹¹ and Diabetes Knowledge Questionnaire-24.⁹ However, these tools are were created for use in patients of all ages. Matricciani et al (2015) reported that foot care practices are underutilized as primary prevention by older adults, and this population generally utilized foot care practices only in case of complications.¹² Foot care behavior of older patients with diabetes differs from that of younger patients.¹³ Miikkola et al (2019) reported that foot care behavior in older adults was poor because of their physical difficulties and inadequate knowledge.¹⁴ Given the unique needs and behaviors of older adults, there is a need for a validated tool to assess foot care self-management in this population.

The Foot Care Scale for Older Diabetics (FCS-OD) was developed by Sable-Morita et al (2021) in Japanese. There are 2 versions of the tool: a short version (9 items) and a longer version (22 items).¹⁵ There are 4 subscales for the short version: skin condition, nail clipping, attention to wounds, and relationships with others. The longer version includes 2 additional subscales: attention to feet and self-efficacy.¹⁵ The current study aimed to assess the validity and reliability of both the long and short Turkish versions of the FCS-OD.

Study design

The study was of a prospective design to determine the validity and reliability of the tool.

Sample and settings

The study was carried out at 2 state hospitals in İstanbul and İzmir, Turkey, from February 2022 to January 2023. These cities are the 2 most densely populated cities of Turkey¹⁶; the reason for choosing these cities was the population density and high number of potential participants in these cities. A power analysis according to Bonett’s (2002) formula was used to determine the minimum required sample size.¹⁷ In this analysis, the acceptable level for Cronbach’s alpha (H0), estimated Cronbach’s alpha (H1), coefficient interval, and power were 0.71, 0.797, 95%, and 95%, respectively. The analysis was carried out on a scale evaluating 22 items, and the minimum required sample size was determined to be 132.

Ageing, in most studies and guidelines, has been commonly measured chronologically. In the literature, a person aged 65 years or older is generally referred to as an “older adult” or “elderly.”^18-20 The Organization for Economic Co-operation and Development (OECD) and European Union (EU) also consider the person aged 65 years and older as elderly.^21,22 Although some guidelines and studies define “elderly” as aged 60 years and older,²³ the common definition of older adults in Turkey is those 65 years and older.^24-26 For this reason, only patients aged 65 years or older were included in this study.

The inclusion criteria of the study were (1) aged 65 years or older, (2) a diagnosis of diabetes at least 6 months ago, (3) an absence of any cognitive disorders, and (4) willingness to consent to participate in the study. The patients who had an existing diagnosis of diabetic foot ulcer or had a history of diabetic foot ulcers or amputation were excluded from the study.

Data collection

The data were collected from the patients via face-to-face interviews. Two researchers took part in data collection. Informed consent was read and signed by each patient who participated in the study. A patient identification form, the FCS-OD,¹⁵ DFCSES,⁹ and FSCBSr ¹¹ were used for data collection. The researchers provided printed data collection forms and a room to the patients. All items on the forms were completed by the patients except for hemoglobin A1c (HbA1c) level, which the researchers recorded by using the patient’s electronic medical record.

Patient identification form. The form consists of 18 items and was developed by the researchers in line with the relevant literature.^9-11,15 The form includes the patient’s age, gender, education, marital status, income level, where he/she lives, diagnosis duration, treatment type, treatment duration, HbA1c level, smoking status, alcohol consumption, comorbidities, hospital admission, and follow-ups. The form also includes the self-perceived level of overall health status and quality of life, which patients scored on a scale of 0 (worst) to 100 (best).

FCS-OD. The scale was developed by Sable-Morita et al (2021) for evaluation of Japanese older adults. There are 2 versions of the tool, the long version and the short version. The long version of the tool consists of 22 items within 6 subscales: skin condition, nail clipping, attention to wounds, relationships with others, attention to feet, and self-efficacy. The short version consists of 9 of the longer version’s 22 items and only 4 subscales: skin condition, nail clipping, attention to wounds, and relationships with others. Cronbach’s alpha values of the scales were 0.797 for the short version and 0.879 for the long version.¹⁵

DFCSES. The scale was developed by Quarles in 2005 and adapted to the Turkish society by Kır Biçer in 2011.^9,27 The scale consists of 9 self-care items scored from 0 (feeling not capable) and 10 (feeling most capable). The total score that could be obtained from the scale ranges from 0 to 90 with high scores showing a high level of foot care self-efficacy. Cronbach’s alpha value for the Turkish version of the scale was 0.86.⁹

FSCBS. This is a 5-point Likert-type scale developed by Borges (2008) and adapted to Turkish by Kır Biçer and Enç in 2014.^11,28 The Turkish version of the scale consists of 15 items scored as 1 (never),2 (rarely), 3 (sometimes), 4 (often), or 5 (always). Total scores on the scale may range from 15 to 75 with higher scores showing more positive foot care behavior. Cronbach’s alpha value for the Turkish version of the tool was 0.83.¹¹

Validity and reliability of the Turkish version of the FCS-OD

The tests used in the assessment of the Turkish version of the FCS-OD are presented in Table 1.

Validity of the Turkish version of the FCS-OD. Language validity, content validity, and construct validity were used to assess the validity of the tool for Turkish society.

Language validity/translation. Forward and backward translations were used to assess the language validity. In this method, 5 translators who were fluent in both Turkish and English first translated the tool from the English version into Turkish. Of the 5 translators, 3 were nurses and 2 were endocrinologists. Then, the Turkish versions of the tool were combined by the researchers. This version of the tool was then translated back to English and compared with the original version of the tool.

Expert opinion (content validity. The Davis method was used to assess content validity. In this method, experts scored the items using a 4-point scoring system in which 1 was not relevant, 2 was somewhat relevant, 3 was quite relevant, and 4 was highly relevant.²⁹ Content validity indexes were calculated both at the item level and at the scale level. Item-level content validity indexes (I-CVIs) were computed as the ratio of acceptable scores (3 and 4) to the number of experts. The scale-level content validity index was computed as the sum of the I-CVIs divided by the total number of items. Veneziano (1997) reported that I-CVIs need to be 0.75 or higher if 9 or more experts scored the items.³⁰ In the current study, 9 experts (6 nurses, 2 endocrinologists, and 1 podiatrist) scored the items regarding their content.

Construct validity. To assess the construct validity of the Turkish version of the FCS-OD, exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used. To assess the identity of the matrix of EFA, the Kaiser-Meyer-Olkin test and Bartlett’s test of sphericity were used. To assess the model of CFA, the goodness of model fit indices were used. The model fit indices evaluated in the study were chi-square goodness of fit, standardized root mean square residuals (SRMR), goodness of fit index (GFI), adjusted goodness of fit index (AGFI), comparative fit index (CFI), and root mean square error of approximation (RMSEA). Factor loadings for each item were assessed to investigate the construct of the scale and subscales.

Reliability of the Turkish version of FCS-OD. In the assessment of the reliability of the Turkish version of the scale, Cronbach’s alpha value, item-scale correlations, parallel form reliability, and test-retest correlations were used.

Cronbach’s alpha. Cronbach’s alpha is the most commonly used test to assess the internal consistency of the Likert-type scales. The values range from 0 to 1 with high values showing a higher level of internal consistency on the scale. Cronbach’s alpha values were assessed for the scale and subscales.

Item-scale correlations. This analysis shows the correlation between each item and the scale and is used to assess the internal consistency of the scale. A high level of correlations between the items and scale shows a high level of internal consistency. The scores of the correlations range from -1 to 1.

Parallel form reliability. Parallel form reliability was used to assess the stability of tool.³¹ There are 2 valid and reliable tools used in Turkey to assess foot care in diabetic populations: the DFCSES and the FSCBS. The correlations between the Turkish version of the FCS-OD and these 2 valid and reliable tools were used to determine parallel form reliability. A high level of correlation shows high consistency between the tools.

Test-retest. Test-retest is another way of determining the stability of the tool by administering the same test twice to the same individuals within a predefined time period. The Turkish version of the FCS-OD was administered to the same participants at an interval of 3 weeks. To determine the minimum required sample size for this method, the calculation reported by Bujang and Bahrum (2017) was used. The minimum required number of participants for this test was calculated to achieve an intraclass correlation efficient >0.50 with a power of 90%, estimated with a 95% confidence interval.

Statistical Analysis

SPSS v26 and SPSS Amos v24 (IBM Corp) were used for the analysis. Descriptive results of the study are presented in number (n), percentage (%), mean, and standard deviation. To assess the matrix of the exploratory factor analysis, the Kaiser-Meyer-Olkin test and Bartlett’s test of sphericity were used. To evaluate the CFA model, the goodness of model fit indices were used. The analyses excluded 17 patients because of missing data. Results were considered statistically significant at P < .05.

Ethics

Written permissions from the Bahçeşehir University scientific and publications ethics committee (approval number E-20021704-604.01.02-25664; approval date February 2, 2022), the hospitals, and the participants were obtained. All participants read and signed informed consent. All principles of the Helsinki Declaration were followed throughout the study.

The gender distribution of the participants was nearly equal (50.6% male and 49.4% female), and the mean age was 73.02 ± 4.61 years. Most of the patients had a primary school education level (64.5%), were living in the city (91.3%), and were married (75.0%). The majority had been treated with a combination of insulin and oral antidiabetic drugs (60.5%). Other sociodemographic and disease-related characteristics of the patients are presented in Table 2.

Patient population

A total of 212 older patients with diabetes were evaluated in the hospital’s outpatient department during the study time frame. Of these, 17 patients were excluded from the analysis because of missing data. Fourteen patients declined to participate in the study. Four patients were excluded because of the presence of an active diabetic foot ulcer or a history of diabetic foot ulcer. Two patients were excluded from the study because of a history of cognitive disorder (advanced dementia); these conditions were initially identified in their electronical health records and confirmed and recorded by a neurologist.

Two patients whose native language was Arabic required a translator provided by the hospital. However, the study authors felt that translation of the tool to Arabic for these patients would compromise the validity and reliability analyses of the Turkish version of the tool. For this reason, these 2 patients were excluded. In total, the study was completed with the participation of 172 patients.

Findings on validity of the Turkish version of FCS-OD

Item- and scale-level content validity indexes were assessed. The item-level content validity indexes ranged from 0.889 to 1 for both long and short versions. Scale-level content validity indexes were 0.964 for the long version and 0.975 for the short version. Findings on the EFA are presented in Table 3.

There were 2 CFAs performed, one for the long version and one for the short version. The goodness of model fit indices for both models were at acceptable levels. Factor loadings ranged from 0.430 to 0.993 for the long version and from 0.417 to 0.994 for the short version (Table 4, Figure 1, and Figure 2).

Findings on reliability of the Turkish version of FCS-OD

Cronbach’s alpha values were 0.905 for the long version and 0.802 for the short version. For the subscales of the long version, Cronbach’s alpha values were as follows: skin condition, 0.907; nail clipping, 0.835; attention to wounds, 0.707; attention to feet, 0.790; relationships with others, 0.730; and self-efficacy, 0.758. For the short version of the scale, the Cronbach’s alpha values were as follows: skin condition, 0.816; nail clipping, 0.985; attention to wounds, 0.707; and relationships with others, 0.730.

There was a statistically significant correlation between the Turkish versions of the FCS-OD and parallel forms of the DFCSES and the FSCBS. For the subscales, there was a statistically significant correlation between the parallel forms and subscales, except for the relationship with others subscale (Table 5).

For the long version, item scale correlations ranged from 0.364 to 0.835, and item scale correlations to the short version ranged from 0.389 to 0.835. There were not any statistically significant differences between the test and retest for both scales and their subscales (Table 6).

Older patients with diabetes are at greater risk for complications than their younger counterparts. Fawzy et al (2019) reported that the risk for the development of foot ulcers increased with age (odds ratio: 4.1) and disease duration (odds ratio: 6.5).³² Similarly, Aboelezz et al (2021) reported that patients with low education status and prolonged disease duration are at risk for the development of diabetic foot ulcers.³³ Foot care is one of the main interventions in the prevention such ulcers; however, the foot care practices, knowledge, and behaviors of older adults are different from those of younger patients with diabetes. For this reason, there is a need for a tool to assess foot care self-management in older patients. This study was carried out to assess the psychometric evaluation of the Turkish version of the FCS-OD.

To assess the foot care practices of the participating patients, 2 scales have been demonstrated to be valid and reliable for Turkish society: the DFCSES and the FSCBS. The DFCSES is used to assess the patient’s perceived capability of performing their foot care practices,⁹ and the FSCBS is another scale commonly used in Turkish society to assess self-care behaviors in foot care.³⁴ However, neither of these tools is specific for the challenges facing older patients with diabetes. Similarly, in the literature, these scales lack a comprehensive evaluation of foot care practices in older adults. After a review of the literature, Sable-Morita et al (2021) highlighted the need for a scale that provided comprehensive foot care evaluation in older adults and, with an expert panel, developed the FCS-OD to evaluate “the ability of older patients with diabetes to manage their foot care.”¹⁵ While developing the FCS-OD, they incorporated 11 of 12 items from the Japanese version of the Foot Care Confidence Scale (JFCCS).¹⁵ The tool was reported a valid and reliable for the comprehensive evaluation of the ability of older Japanese patients with diabetes to manage their foot care. The tool has 2 versions: the short version consisting of 9 items and a longer 22-item version.¹⁵

In the current study, the mean age was 73.02 ±4.61 years, and mean HbA1c (%) level was 9.40 ± 1.90. The mean age was similar to that of patients who participated in original scale development; however, the mean HbA1c of patients in the current study was higher than that of the Japanese study participants.¹⁵ According to the literature, the mean HbA1c has been reported to be 8.5% in older Hong Kong Chinese³⁵ patients with diabetes, and  65.1% of older Mexican-American patients with diabetes have poor glycemic control (defined as HbA1c exceeding 7%).³⁶ In Turkey, Kara (2017) reported that the mean HbA1c of older Turkish adults with type 2 diabetes was 8.2%.³⁷ Furthermore, Acar et al (2014) reported that there was a strong positive correlation between Turkish patients’ age and their HbA1c level.³⁸ Ersoy et al (2020) reported that  Turkish older adults engage in a low level of physical activity.³⁹ In addition, most older adults reported that their level of physical activity decreased during the COVID-19 pandemic.⁴⁰ These factors may explain the high HbA1c levels in the current study.

In the current study, the mean duration of diabetes was 168.99 ± 99.80 months, which corresponds to approximately 14 years. The mean duration of the current treatment regimen was 140.46 ± 74.71 months, which corresponds to approximately 12 years. In a study carried out with geriatric patients with type 2 diabetes, disease duration was over 10 years for more than half of the participants.⁴¹ On the other hand, in this study, the mean age of the patient was 73.02 ± 4.61 years, and mean disease duration was approximately 14 years; therefore, the mean age of diagnosis was about 59 years. Zoungas et al (2014) reported that the mean age of diagnosis was 57.8 ± 8.7 years.⁴² The current study’s findings reflect the literature regarding the disease duration.

Treatment regimen in the current study was classified as follows: insulin, oral antidiabetic drugs, and combination therapy with insulin and oral medication. In the absence of metabolic decompensation, oral antidiabetic drugs (especially metformin) are suggested for the adults with type 2 diabetes.⁴³ However, in cases of poor glycemic control, a combination of insulin and oral antidiabetic medications is suggested for these adult patients.⁴⁴ In the current study, the mean HbA1c was 9.40, meaning that most of the patients had poor glycemic control.⁴⁵ Consistent with this finding, most of the patients (60.5%) were receiving combination therapy.

In the current study, most patients had primary school level of education, and approximately 3 out of every 4 patients reported that their income was less than their expenses. Education level and income are 2 important components of socioeconomic status, which is an important predictor of outcomes in patients with diabetes.⁴⁶ The authors believe that socioeconomic status could be an explanation for the generally low education and income level in the current study. In addition, the study was carried out in 2 densely populated cities in Turkey; urbanization in these 2 areas is high, and most of the patients in this study were living within city limits.¹⁶ This may be a further contributing factor for the current study findings. Furthermore, this is a limitation for the study regarding its generalizability. For this reason, further studies should be conducted in towns and villages.

In the current study, the marital status of the participants was investigated under 2 categories: single or married. Approximately 3 out of 4 participants were married. In a study by Ramezanhkani et al (2019), it was reported that risk of type 2 diabetes was lower in widowed women.⁴⁷ Contrary to that study, de Oliveira et al (2020) reported that the risk for type 2 diabetes was lower in individuals who remained married despite having significantly increased their weight.⁴⁸ Lima et al (2014) reported that the more married individuals were overweight compared with singles, and high blood glucose levels were more common in married participants.⁴⁹ There is no agreement on the relationship between marriage and diabetes risk. The reason for this is that the classification of marital status varies across countries. In Turkey, marital status is legally divided into only the 2 categories of married and single.

In this study, it was found that smoking and alcohol use was low in elderly patients with diabetes. Other research has indicated that individuals with type 2 diabetes continue to engage in risky behaviors like smoking or alcohol consumption.⁵⁰ Alcohol consumption and smoking were reported among the determinants of diabetic foot ulcer.⁵¹ The current study was carried out with patients who did not display these complications. For this reason, smoking and alcohol consumption may be moderate or high in patients with type 2 diabetes if patients with a diabetic foot ulcer were not excluded. Further studies are needed to investigate this relationship in Turkish society.

Most patients with diabetes have a comorbidity, a history of unplanned hospital admission in the last 6 months, an unplanned hospitalization, and/or failure to adhere to a regular follow-up schedule. Soh et al (2020) reported that older patients (≥ 65 years) with diabetes have higher risk for unplanned hospital readmission compared to younger adults (< 65 years).⁵² The reason for the high unplanned readmission to the hospital may be related to medical comorbidities and lower level of health literacy of older adults.⁵² Albrecht et al (2014) reported that age is highly associated with patient adherence to regular follow-up appointments.⁵³ In the current study, the patients had poor glycemic control; Anjana et al (2015) reported that patients who had regular follow-up had better glycemic control.⁵⁴

In the current study, patients’ perception of their overall health status and quality of life was moderately positive. In another study conducted in a similar population, the patients’ perceived quality of life and health status was also reported at a moderate level.⁵⁵ Perceived health status is a subjective way of assessing health in patients with diabetes and has been found to correlate consistently with objective parameters.^56,57

The I-CVIs ranged from 0.889 and 1 while the S-CVIs were 0.964 and 0.975 for the long version and short version, respectively. Veneziano (1997) reported that the I-CVIs and S-CVIs should be over 0.75 if 9 or more experts scored the scale.³⁰ In the current study, 9 experts scored the items. Therefore, CVIs were at an acceptable level both for the long version and the short version.

EFA shows that both the long and short versions of the scale were explaining more than 50% of the total variance with their original structure. KMO values were 0.798 and 0.878 while Bartlett’s test of sphericity was statistically significant for both the long and short versions of the scale. Beavers et al (2013) reported the interpretation of the KMO as follows: 0.90 to 1.00, marvelous; 0.80 to 0.89, meritorious; 0.70 to 0.79, middling; 0.60 to 0.69, mediocre; 0.50 to 0.59, miserable; and 0.00 to 0.49, don’t factor. Bartlett’s test of sphericity showed that the correlation matrix was statistically different from a singular matrix, confirming that linear combinations exist.⁵⁸ Model fit indices of the CFA were at acceptable levels.^59,60 Factor loadings ranged from 0.430 to 0.993 for the long version and from 0.417 to 0.994 for the short version. All items in the short version and long version of the scale were over the acceptable level (> 0.40) reported in the literature.^59,60 The construct of the scale was considered suited for Turkish society according to the EFA and CFA results.

Cronbach’s alpha is the most common way to assess the internal consistency of Likert-type scales. Cronbach’s alpha values for the Turkish versions were 0.905 for the long version and 0.802 for the short version. For the subscales, Cronbach’s alpha values ranged from 0.707 to 0.985. According to George and Malley (2003), the interpretations for Cronbach’s alpha were as follows: ≥ 0.9, excellent; ≥ 0.8, good; ≥ 0.7, acceptable; ≥ 0.6, questionable; ≥ 0.5. poor; and ≤ 0.5, unacceptable.⁶¹ According to Malley’s classification, the internal consistency of the long version was excellent and the short version was good. In the development study of the scale, Cronbach’s alpha values were reported as 0.879 for the long version and 0.797 for the short version.¹⁵ The internal consistencies of the subscales were over acceptable levels.

Another analysis used in the current study to assess internal consistency was item-scale correlations. Item scale correlations ranged from 0.364 to 0.835 for the long version and from 0.389 to 0.835 for the short version. Item-scale correlation over 0.2 is considered acceptable for internal consistency.⁶² According to the item-scale correlations, the scale shows acceptable internal consistency.

To assess the stability of the scale, test-retest analysis, and parallel form reliability were used. There were statistically significant moderate to high correlations between the parallel forms and scales/subscales except for the relationship with other subscales. The authors believe that the low correlation between other subscales and the parallel forms may be attributed to no corresponding items in the scales used as parallel forms.^9,11 Both the long and short versions of the scale showed moderate to high consistency with parallel forms that have been reported to be valid and reliable for Turkish society, showing the stability of the FCS-OD. Furthermore, there were no statistically significant differences between the test and retest for the short and long versions of the tool and their subscales, which also shows the stability of the scale over time.

The study was carried out in 2 hospitals, and as such the generalizability of the study is limited. The enrolled patients consisted only of the older patients with diabetes who were admitted to these hospitals; the study was not community-based. Details on patient demographics such as marital status and smoking history were not investigated, which limits comparisons to the Japanese version of the tool.

Both the long and short versions of the scale were found to be valid and reliable for Turkish society. The scales showed high internal consistency and stability. Cronbach’s alpha values were 0.905 for the long version and 0.802 for the short version. The long version is suggested for a complete assessment of patients, whereas the short version is suggested for initial screening. The authors recommend the use of the scale in the assessment of older patients with diabetes by clinicians and in additional research studies with larger and different populations.

Affiliations: ¹Fethiye Faculty of Health Sciences, Muğla Sıtkı Koçman University, Muğla, Turkey; ²Endocrinology and Metabolic Disorders Department, Göztepe Prof. Dr. Süleyman Yalçın City Hospital, İstanbul, Turkey; ³Department of Nursing, Bahçeşehir University, İstanbul, Turkey; ⁴Medical Nursing Department, Ege University, İzmir, Turkey

Disclosures: The authors disclose no financial or other conflicts of interest.

Correspondence: Ismail Toygar, PhD; Muğla Sıtkı Koçman University, Fethiye Faculty of Health Sciences, 3rd Floor, 48330 Fethiye/Muğla, Turkey; ismail.toygar1@gmail.com

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