Health has been traditionally conceptualized as a biological function at typical levels of efficiency [1]. However, health, as defined by the WHO, is not just the absence of sickness, but rather the presence of complete well-being [2]. As chronic diseases rise, several researchers suggested redefining health. Health is the ability to adjust to social, physical, and emotional obstacles [3]. In some instances, the medical literature also mentions a third status, which is described as non-disease and non-healthy [3]. Several states of physical discomfort and signs that could not be clearly described as diseases were listed in the ICD-10. These vague health conditions were ascribed as ‘sub-optimal health status’ (SHS) by scholars; later, in 2009, a team of Chinese researchers developed a tool to measure this health status [4]. The construct of SHS has been described as a sub-clinical state where a person is neither experiencing sickness nor is healthy, and there are apparent signs of discomfort [5], which may lead to adverse health outcomes [6]. Since the definition of health has several implications for health policy, practices, and healthcare services, it is essential to define and appropriately measure various states of health and well-being. Recently, scholars and clinicians have pointed out that the current definition of health by the WHO needs to be revisited, in order to deal with emerging challenges in the health system, lifestyle factors, and environmental issues that impact the health and well-being of individuals [7].

SHS has been conceptualized by Feng [8] under the health model, which encompasses biological, psychological, and social domains of health. Low quality of health status without any apparent disease condition experienced by individuals in health domains is considered a sub-health condition. In the physical domain, it presents itself as poor functioning of the body and organs, along with diminished energy levels; deprivation of emotional and cognitive resources for functioning relates to the psychological domain; and in the social domain, it is depicted by non-availability or poor utilization of social resources that may hamper some aspects of social functioning.

Many developed countries, including Saudi Arabia, are undergoing vivid shifts due to fast-paced economic growth, which impacts lifestyles and social systems. The literature from other high-income countries has pointed out that unhealthy lifestyles significantly impact health, and mainly increase the vulnerability for sub-optimal health status [9]. Among the reasons, currently, both a high number of men and women in the workforce are exposed to work pressures and risk for work–family imbalance, and the COVID-19 epidemic has had a negative effect on people’s standard of living in several domains and may have increased the risk of developing SHS ^[10][11][10,11].

SHS is a heightened concern for medical professionals and public health experts because it is a significant risk marker for chronic illnesses. SHS is differentiated from a sub-clinical disease state because it is a low-quality health state that cannot be classified as a disease state [3]. The signs and symptoms experienced by individuals at the onset of mental and psychological disorders have proximity to symptoms of SHS and must be differentiated thoroughly. SHS is usually demonstrated by deterioration in physiological, emotional, and social functioning, leading to a decline in vitality, adaptation, and resilience. According to the diagnostic guidelines provided by the Association of Chinese Medicine [12], symptoms in three areas, namely, systematic, psychological, and social, are evaluated to assess SHS. Among core physical and psychological symptoms are body aches and pain, tiredness, disturbed sleep, low mood, irritability, restlessness, reduced focus, and memory problems. Individuals also experience a decline in interest and engagement in social activities. The decision to diagnose SHS in any three dimensions is made, if an individual experiences symptoms over the previous three months without a baseline disease condition. However, this approach was less accepted due to its subjectivity and was not employed in clinical diagnosis [13].

Different quantitative, qualitative, and mixed approaches have been used to measure SHS ^[14][15][14,15]. Among the quantitative measures, self-rating scales and checklists have been commonly used, among which are the Suboptimal Health Status Questionnaire- 25 (SHS-25) ^[4][16][4,16] and the sub-health Measurement Scale V1.0 [17]. The comprehensive assessment of SHS also includes measuring stress response using biochemical methods; stress response is considered a causal mechanism that increases the risk of experiencing SHS [18]. Furthermore, a study demonstrated that people with SHS were more likely to report symptoms of fatigue and pain [19]. There are two categories of measures used in determining the SHS. Among the objective indicators are biochemical and anthological-physiological indicators, such as C-reactive protein (CRP), low-density lipoprotein (LDL), high/low blood pressure (BP), and high/low body mass index (BMI). In current medical practice, subjective measures are employed for the clinical diagnosis of SHS after a comprehensive physical examination that excludes specific illnesses. In public health research, self-report measures are widely used to assess SHS.

Interestingly, there are also controversies about whether the measurement of SHS aligns with the SHS theoretical framework, which assumes that environmental factors and psychological states determine SHS, and betterment in these factors should alleviate SHS [16]. Therefore, SHS is seen as a reversible health condition, compared to disease conditions that have progressed toward worsening symptoms.

SHS has now been recognized as an essential construct in personalized medicine to decrease the risk of developing disease and enhance general health. Moreover, the idea of SHS reflects the belief that chronic diseases can be effectively predicted and prevented before a clinical manifestation of severe pathologies from the view of predictive, preventive, and personalized medicine ^[3][5][3,5]. It is crucial to have reliable tools to assess SHS, which can be used in clinical practice and community health research. RWesearchers h have noticed that there are limited tools, an ongoing debate about the definition and measurement of SHS, and inconclusive evidence about the psychometric properties of tools to measure SHS ^[20][21][20,21]. Despite the diagnostic standards and assessment of SHS having been shifted to objective indicators, there are unresolved issues related to the appropriateness of measures used in assessment due to the wide range of symptoms, the intensity of symptoms experienced, and their link with many diseases’ conditions ^[20][21][22][20,21,22].

2. Suboptimal Health Status Questionnaire-25 (SHSQ-25)

2.1. Description of the SHSQ-25

The SHSQ-25 is the most commonly used SHS screening tool. China’s Capital University of Medical’s Wei Wang group invented it in 2007 ^[3][4][3,4], and readily articulated and operationalized it in 2009 ^[23][28]. The questionnaire is the outcome of a focus group discussion with apparently healthy individuals, an extensive literature search, and expert opinions [4]. The SHSQ-25 was developed to screen and take into account multidimensional health constructs that could indicate people were feeling poor health and acquired chronic stress. The authors formulated a questionnaire containing 25 items in five domains: (1) fatigue (9 items), (2) the cardiovascular system (3 items), (3) the digestive tract (3 items), (4) the immune system (3 items), and (5) mental status (7 items) ^{[3][4][15][23][24]}[3,4,15,24,28]. It assessed how often individuals suffered from several specific discomforts in the previous three months [24]. The SHSQ-25 is rapid and easy to complete; therefore, it is appropriate for the general population and healthcare settings ^[4][13][15][4,13,15]. It has been applied and validated in various populations, including Chinese, African, and European ^[25][23]. Despite widespread applications of the SHSQ-25, most studies explore psychometric properties only in the Chinese population and, recently, in Ghanaian and Korean populations ^[23][26][27][28,29,30].

2.2. Scoring System for the SHSQ-25

SHSQ-25 items are scored on a 5-point Likert scale, from never to always ^{[5][19][28][29]}[5,19,31,32]. The total score is the aggregate of all 25 questions, scored from 0 to 4 ^{[4][5][14][16]}[4,5,14,16]. SHS screening uses the upper limit of a unilateral 90% reference value (X + 1.28S), if the population’s SHS score follows a normal distribution [4]. The percentile and the unilateral P90 value’s upper limit will be used if it does not follow a normal distribution [4]. The SHSQ-25 considers all important factors that affect SHS; hence, the cut-off point is 35 points, the highest limit of the unilateral P90 value [4].

2.3. Reliability and Validity Indicators of the SHSQ-25

Researchers found four studies assessing the instrument’s internal consistency and test–retest reliability. Yan et al. (2009) examined 3000 Chinese individuals, and found item-sub-scale correlations ranging from 0.51 to 0.72, and a Cronbach’s α 0.93 for all sub-scales [4]. Furthermore, Wang and Yan (2012) [15] found a higher Cronbach’s α value (0.91) for internal consistency among 3045 Chinese individuals. Interestingly, Adua, et al. (2021) ^[23][28], while assessing the internal consistency of SHSQ-25 among 263 healthy Ghanaians, found Cronbach’s α for each category as follows: fatigue = 0.846, immune-cardiovascular = 0.820, and cognitive = 0.864 ^[23][28]. Only one study had test–retest reliability with coefficient values of 0.89 to 0.98 [4]. Adua, et al. (2021) assessed the validity, and the findings revealed a construct validity > 0.7 thresholds ^[23][28]. Meanwhile, convergent and discriminant validity values were as follows: fatigue (AVE = 0.366, MSV = 0.701), cognitive (AVE = 0.358, MSV = 0.671), immune-cardiovascular (AVE = 0.537, MSV = 0.185. Recently, a study validated the Korean Septimal Health Questionnaire (KSHSQ-25), and the findings revealed that the test–retest reliability’s range was 0.88–0.99, a Cronbach’s α of 0.953, and a Cronbach’s α for each domain ranged from 0.76 to 0.94 [30], as ^[27]shown in Table 2.

3. Sub-Health Measurement Scale V1.0 (SHMS V1.0)

3.1. Description of the SHS V1.0

The second instrument was the Sub-Health Measurement Scale V1.0. It is a self-reported multidimensional inventory designed to assess physiological, psychological, and social symptoms to determine SHS. This inventory was devised by researchers in China ^[28][31]. The inventory consists of a total of 39 items. The first four items are used to evaluate individual general health, and the remaining thirty-five items are divided into three dimensions ^[27][30]. The dimension of physiological symptoms encompasses four factors, which are physical condition, organ function, body movement function, and vigor; these factors are assessed through a set of fourteen questions ^[30][33]. The psychological dimension of symptoms contains three factors, which are positive emotions, psychological symptoms, and cognitive functions, and are assessed through a set of twelve questions ^[27][30]. The social dimension includes three factors, which assess social adjustment, resources, and support, and comprises a set of nine questions. The SHMS V 1.0 has been widely used to determine the SHS of participants, especially among nurses, urban residents, college students, and midwives ^{[9][29][31][32][33][34]}[9,32,34,35,36,37]. The scale was proven to have good psychometric properties in these studies ^{[28][35][36][37]}[31,38,39,40].

3.2. Scoring System for the SHMS V1.0

The SHMS V1.0 has a straightforward scoring system. On a five-point Likert scale, from 1 (never) to 5 (often), respondents are asked to rate how often they experienced various types of discomfort over the past six months ^[30][33]. A set of items comprises three dimensions, and the total sub-score sums up the score on each dimension. The transformed score is computed using the score conversion formula. The converted score lies between 0 and 100, and represents the health status ^[30][33]. A lower total score is interpreted as a worse health status. The cut-off scores are used to differentiate between individuals with positive health and SHS on all three dimensions ^[38][41]. These are 66.1, 52.1, and 55.6 for physiological, psychological, and social dimensions, respectively ^[33][36]. If the score for these three dimensions is found to be lower than the cut-off, the participant is categorized as having physiological, psychological, and/or social health SHS. In another study ^[36][39], the mean, percentile, and threshold norms were established. According to sex and age brackets (14–19, 20–29, 50–64, and 65), norms for the total, physical, mental, and social sub-health of Chinese urban residents were calculated. Computing the mean ± SD and mean ± 0.5SD of the transformed scores yields the threshold norms of SHMS V1.0’s five health states: illness, severe SHS, moderate SHS, mild SHS, and positive health ^[38][41].

3.3. Reliability and Validity Indicators of the SHMS V 1.0

Researchers found five studies assessing SHMS V 1.0 psychometric properties; the structural validity showed a high correlation between an item and dimensional scores (0.656 to 0.878). The correlation between each dimension and sub-scale scores was strong (0.586 to 0.868) ^[39][42]. Researchers found that the reliability of the SHMS V 1.0 was 0.917. The first study’s Cronbach α coefficient was 0.92, and the split-half coefficient was 0.83 ^[28][31]. A recent study in Tianjin found that the test–retest and overall Cronbach’s coefficients were 0.67 and 0.92, respectively. In addition, the correlation between the SHMS v1.0 and SF-36 was 0.78 (p < 0.01) ^[37][40].

4. Multidimensional Sub-Health Questionnaire of Adolescents (MSQA)

4.1. Description of the MSQA

TheOur systematic search found the MSQA, an adolescent assessment tool, as the third SHS instrument. Chinese researchers developed a self-reported questionnaire to assess teenage psychological problems ^[30][33]. The MSQA assesses uncomfortable symptoms experienced by respondents in the past three months, and includes 71 items divided into six symptom dimensions: lack of physical energy (11 items), physiological dysfunction (11 items), weakened immunity (10 items), emotional symptoms (17 items), behavioral symptoms (9 items), and social adaptation problems (13 items) ^[40][43]. Each item has six answer categories: none or last <1 week, 1 week, 2 weeks, 1 month, 2 months, and 3 months ^[40][43]. Emotional and behavioral symptoms are measured using 17 and 9 items, respectively. There are 13 items that measure social adaptation issues (e.g., “always disliked school”) ^[28][31].

4.2. Scoring System for the MSQA

The MSQA measures emotional, behavioral, and social symptoms ^[28][31]. Summing item scores yields the final scores. Summing the 39 item scores yields psychological symptoms. The MSQA National Norm Development ^[30][33] sets the psychological symptom cut-off at the 90th percentile for all adolescents. Emotional, behavioral, social adaptability, and psychological symptoms have cut-off values of 3, 1, 4, and 8, respectively ^[28][31]. The MSQA also evaluates psychophysiological functioning. The MSQA has 39 questions on three dimensions based on symptoms experienced in the past three months: 17 for emotional symptoms (e.g., “Do you always feel nervous?”), 9 for behavioral symptoms (e.g., “Do you always have the impulse to damage something?”), and 13 for social adaptation problems (e.g., “Were you always not suited to school life?”) ^[41][42][44,45]. All questions include six response alternatives based on symptom duration: none, last <1 week, last 1–2 weeks, last 1 month, last 2 months, last 3 months ^[28][31]. The symptom duration “last 0–1 week” was converted into “1” (positive items) and “none or last <1 week” into “0” (negative items) ^[41][42][43][44,45,46]. Psychopathological symptoms required eight or more “1” scores ^[42][45].

4.3. Reliability and Validity Indicators of the MSQA

ResWearchers found four studies assessing the psychometric properties of the MSQA. The test–retest reliability was around 0.87 in three studies. Moreover, the Cronbach alpha coefficient and split-half reliability were around 0.96 and 0.94, respectively ^{[30][40][41][42][44]}[33,43,44,45,47]. The total scale of Cronbach’s α for physiological, psychological, and social components demonstrated good reliability at 0.91, 0.85, and 0.85, respectively ^[33][36].

5. Sub-Health Self-Rating Scale (SSS)

5.1. Description of the SSS

The search retrieved the Sub-Health Self-Rating Scale (SSS), which Chinese researchers developed to assess the SHS of university students ^[31][34]. It determines the SHS of individuals by assessing three dimensions of health (physiological, psychological, and social). A total of 58 items comprises the scale, and scoring is conducted on ten labelled factors (F1 to F10). The physiological dimension symptoms include six factors: sleep, fatigue, skin, pain, digestive, and urine, which are labelled F5, F7, F9, F3, F4, and F10, respectively. The social encompass dimension symptoms comprise two factors: F6 and F8, capability and self-respect factor, and social relationship factor, respectively. The psychological dimension symptoms contain two factors: F2—passive feeling factor, and F1—positive feeling factor ^[39][42].

5.2. Scoring System for SSS Measures

The SSS is scored by adding the raw scores on items or sub-scales ^[39][42]. Each item contains five answer categories for symptom severity (never = 5, occasionally = 4, sometimes = 3, constantly = 2, and always = 1). Before adding the scores, the 16 symptoms are inversely converted. The converted score is the raw score minus the lowest possible sub-scale or total scale score, divided by the highest possible score minus the lowest. The T score measures test score variability as (X + −X)/S, where X is the raw score, −X is the overall mean score, and S is the population standard deviation ^[39][42].

5.3. Reliability and Validity Indicators of the SSS

The SSS’s psychometric qualities were assessed using the Cronbach α coefficient of 0.942 ^[39][42]. The reliability for each physiological, psychological, and social dimension was reliable: 0.915, 0.856, and 0.850, respectively ^[39][42]. The Bartlett test of sphericity showed validity (2 = 7778.7; p = 0.000), and the Kaiser–Meyer–Olkin (KMO) score of sample adequacy was 0.94. To sum up, the systere are matic review of articles on SHS measurement tools demonstrated some evidence about the psychometric properties of instruments; most of them were based upon studies from China. Among the reliability indicators, three parameters were commonly reported: (1) the internal consistency measured by Cronbach’s α value ranged between 0.71 and 0.96; (2) the test–retest reliability ranged from 0.64 to 0.98; and (3) the split-half reliability coefficient values ranged between 0.64 and 0.98, and between 0.83 and 0.96, respectively. All three indicators of reliability revealed acceptable levels of evidence about the reliability of these measures. The indicators of the validity of tools were determined through (1) construct validity, (2) convergent validity, and (3) divergent validity, and it was accomplished for three subjective measures, namely the SHSQ-25, MSQA, and SSS. For the validity coefficient values in the case of SHSQ-25 > 0.71, SHMS-1.0 ranged from 0.64 to 0.87, and SSS ranged from 0.74 to 0.96, and can be considered as acceptable.