Incidence and persistence of psychological distress during the COVID-19 pandemic among individuals with and without disability

Objectives We investigated the incidence (becoming distressed at the follow-up) and persistence (distressed at the baseline and the follow-up) of psychological distress among individuals with and without disability in the period from early 2017 (before the COVID-19 pandemic) to late 2020 (the second wave of the pandemic). Methods We analyzed the population-based FinHealth 2017 survey and its follow-up conducted in 2020 (number of individuals who participated in both surveys: n = 4881; age = 18+). Logistic regressions were applied to investigate differences in the incidence and persistence of psychological distress between people with and without disability. We also investigated whether age, quality of life at the baseline, and perceived increase in loneliness during the COVID-19 pandemic moderated the association between disability and the incidence of distress. Results The incidence of psychological distress was higher (OR = 3.01, 95% CI:2.09–4.35) for people with disability (18.9%) than among those without (7.4%), being highest (31.5%) among the youngest participants with disability, aged 18 to 39. People with disability who had a poor quality of life at the baseline were particularly prone to become distressed during the follow-up. People who reported perceived increase in loneliness during the pandemic were prone to become distressed at the follow-up regardless of their disability status. The persistence of distress was more common (OR = 6.00, 95% CI:3.53–10.12) among people with disability (65.7%) than among those without (24.9%). Conclusion The COVID-19 pandemic had more negative mental health effects on people with disability, especially adults with disability who were young and had a low quality of life before the pandemic.


Introduction
Psychological distress tends to have a detrimental effect on health and represents an increased mortality risk [1]. The COVID-19 pandemic has increased psychological distress and related symptoms (anxiety, depression, and stress) among the general population [2][3][4][5][6][7][8]. However, there is limited evidence on the incidence (psychological distressed during but not before the pandemic) and the persistence of psychological distress (during and before the pandemic) [9][10][11]. An international follow-up study indicated that on average about one in ten began to experience psychological distress symptoms during the pandemic [9]. The incidence of depressive disorder was higher during the pandemic than before among older people [10].
Less information is available on changes in psychological distress among people with disability during the pandemic compared to the time before it. Some cross-sectional studies have indicated that during the COVID-19 pandemic psychological distress and symptoms were more common among people with disability than among those without [12][13][14][15][16][17][18], but there were significant differences in mental health between people with and without disability even before the pandemic [19][20][21][22]. Nevertheless, during the pandemic, many factors exacerbating psychological distress-for example, loneliness, social exclusion, inadequate health and social services, serious illness from COVID-19, hospitalization, and a poor financial situation-worsened more among people with disability than among those without [17,18,[23][24][25][26]. There is also some evidence that people with disability reported increased stress more often during the pandemic than those without [27], while one study found that disability was not significantly associated with increased anxiety or depression during the pandemic [28]. Although these studies suggested that the incidence and persistence of psychological distress during the pandemic may be higher among people with disability than among those without, the evidence on this is limited.
There is evidence that certain adverse factors predict incidents of psychological distress. A follow-up study found that preceding low level of life satisfaction predicted subsequent psychological distress symptoms in the general population [29]. Another longitudinal study indicated that a poor quality of life-including satisfaction with health, ability to perform daily living tasks, personal relationships, living arrangements, and having enough energy-predicted symptoms of psychological distress, but an inverse connection of these variables was not observed [30]. Although a lower quality of life is related to higher psychological distress and its symptoms among the general population [29][30][31][32][33][34], there is limited research conducted on people with disability. People with disability have reported a lower quality of life more often than those without [35,36]. Therefore, it is important to investigate whether a low quality of life at the baseline among people with disability may increase their risk of becoming psychologically distressed by the time of the follow-up. Previous studies have reported that the pandemic increased loneliness for people with disability more often than among those without [18,23,28], while a high level of loneliness was a key contributor to psychological distress among the general population during the pandemic [37][38][39]. Therefore, perceived increase in loneliness among people with disability during this period may also increase their risk of becoming psychologically distressed by the time of the follow-up.
Although cross-sectional studies suggest that the association between disability and psychological distress may have varied across age groups before the pandemic, the findings are inconsistent [18,19]. One study found that older people with disability were more likely to experience psychological distress symptoms [19], while another found that psychological distress was more prevalent among younger people with disability [18]. However, the situation may be different during the COVID-19 pandemic. Previous studies have indicated that psychological distress increased particularly among the younger age group (≤40 years) during the COVID-19 pandemic [3,8,40,41], but the evidence regarding people with disability is limited. Thus, it is important to investigate whether the effects of disability on the incidence of psychological distress during the pandemic vary between age groups.
Based on the above, we investigated differences in the incidence and persistence of psychological distress between individuals with and without disability from the time before the COVID-19 pandemic (2017) until the second wave (2020). We also investigated whether the association between disability and the incidence of psychological distress varied between age groups, quality of life level at the baseline, and perceived increase in COVID-19-related loneliness-that is, the interaction effect of these potential moderators and a disability on the incidence of psychological distress. Investigating the incidence of psychological distress over three years and factors moderating it may provide information to support people with disability regarding their psychological distress.

Data and design
The data came from the FinHealth 2017 survey [42] and its threeyear follow-up [43], conducted by the Finnish Institute for Health and Welfare. The sampling scheme consisted of two-stage, stratified cluster sampling [42]. In the first stage, a sample including 50 health center districts was selected. The second stage involved sampling individuals from those districts from the National Population Register. At the baseline, a questionnaire was sent to a sample of 10,305 Finnish people representing the population aged 18 and over, who were also invited to a health examination. The response rate was 69% (N = 7050; 18+). The follow-up was carried out during the second wave of the COVID-19 epidemic in Finland, at the end of 2020 and the beginning of 2021. During this phase, questionnaires were sent to all members of the 2017 sample who were still alive and living in Finland and had not refused further contact or withdrawn their consent (N = 9580; age 21+). The response rate was 56% (N = 5400). At the baseline and the follow-up, it was possible to answer the questionnaires electronically or in a paper form [42]. In addition, those who had not responded were contacted by phone. The number of persons participating in both surveys was 4881.
Weighting was used in the analyses to restore the population representativeness of the data. The calculation was based on the inverse probability weighting method [44,45] using register-based data for the whole sample for age, sex, marital status, education, geographic area, and native language. The FinHealth 2017 survey and the follow-up were approved by the Ethics Committee at the Hospital District of Helsinki and Uusimaa (reference 37/13/03/00/2016 and HUS/2391/2020).

Disability
Disability was assessed using the Global Activity Limitation Indicator (GALI), which has previously been validated against other disability measures in several European countries [46,47]. The GALI consists of two questions: (a) "Are you limited because of a health problem in activities people usually do? And (b) "Have you been limited for at least the past six months?" The response options for question (a) were "severely limited" (1), "limited but not severely" (2), and "not limited at all" (3); and for question (b), the response options were "yes" and "no." Those who responded being "severely limited" or "limited but not severely" for at least the previous six months were categorized as having disability. In this study, we focused on those who had long-lasting disability, i.e., those having disability in both 2017 and 2020 (n = 1157). Those who did not have disability in either 2017 or 2020 were categorized as having no disability (n = 2455). Those who had disability only in 2017 (n = 528) or 2020 (n = 575) were excluded from the analysis as their disability was considered a short-term limitation.

Outcome variables
Psychological distress was assessed using the Mental Health Inventory-5 (MHI-5) [48]. This indicator is based on five questions:  2), "a good bit of the time" (3), "some of the time" (4), "a little of the time" (5), and "none of the time" (6). The scores for questions (c) and (e) were converted into the reverse order, and the points were added (summary score 5-30). The scale was changed to 0-100 by subtracting five from the summary score and then multiplying the result by four (i. e., [summary score-5] × 4), following the standard used in other studies [48,49]. Lower scores indicating higher psychological distress. The internal consistency (Cronbach's alpha) was good for the MHI-5 data from both 2017 (0.84) and 2020 (0.86). People were defined as having clinically significant psychological distress if their MHI-5 score was 60 or below [49].

Demographic covariates and moderators
We used the following demographic covariates: age (18-39, 40-69, and ≥ 70 years), sex (female and male), living alone (yes and no), working status (employment, unemployment, retired, and others [e.g., student, unpaid internship, family leave]), and education level (low [elementary school/lower secondary school], medium [vocational school/upper secondary school/high school], and high [non-university higher education/bachelor's degree/master's degree]). These demographic covariates were measured at the baseline in 2017. The control variables were selected based on previous studies that indicated these variables to be associated with psychological distress [2,3,15,40,41,50]. We chose the age groups 18-39, 40-69, and ≥ 70 years old to represent young, middle-aged, and older adults, respectively. Further, one meta-analysis showed that people under the age of 40 are at a high risk of psychological distress during the pandemic [3], while another meta-analysis indicated that adults aged 70 years and older are particularly at risk for COVID-19 infection, severe disease, and death [51], which may increase their distress. Thus, these age groups are also important to distinguish.
Age, quality of life at the baseline, and perceived increase in loneliness during the COVID-19 pandemic were considered as potential moderators of the relationship between disability and becoming psychologically distressed between 2017 and 2020 (i.e., the incidence of psychological distress). The quality of life was measured using the EUROHIS-QOL 8-item index [52,53]. This indicator is based on eight items: "(a) How would you rate your quality of life?" (response options: "very poor," "poor," "neither poor nor good," "good," and "very good"); "(b) How satisfied are you with your health? (c) your ability to perform your daily living activities, (d) yourself, (e) your personal relationships, and (f) the conditions of your living place?" (response options: "very dissatisfied," "fairly dissatisfied," "neither satisfied nor dissatisfied," "fairly satisfied," and "very satisfied"); "(g) How completely, in the last two weeks, were you able to do the following: have enough energy for everyday life, and (h) have enough money to meet your needs?" (response options: "not at all," "a little," "moderately," "mostly," and "completely"). All responses were scored 1-5 points and the average of the points was calculated, with higher scores indicating better quality of life. The internal consistency (Cronbach's alpha) was strong for the EUROHIS-QOL 8-item index for data from 2017 (0.86). A three-category variable of the EUROHIS-QOL 8-item index was created to represent low [0,3], medium (range]3, 4]) and high quality of life (range]4, 5]) [54].
Perceived increase in loneliness during the COVID-19 pandemic was identified based on question in the follow-up about the perceived effects of the pandemic and its restrictions on feeling lonely. The response options were "yes, increased"; "yes, decreased"; "no effect"; and "not applicable." We report herein the negative effects, that is, perceived increase in loneliness.

Data analyses
Among persons included in the analysis, there were some missing data on the outcome, demographics covariates and moderators (MHI-5: 7.9%; living alone: 0.6%, working status: 0.3%, education level: 0.2%; loneliness variable: 3.2%, and EUROHIS-QOL 8-item index: 13.6%). However, weighting was used in the analyses considering nonparticipation. The calculation of weights was based on the inverse probability weighing method, which is shown to remove the bias caused by nonresponse [44].
All data analyses were conducted using Stata Version 16. We used the survey analysis procedures of the Stata software to analyze complex survey data by considering the sample design [55]. First, we conducted frequency analyses to examine the prevalence of disability and the sociodemographic characteristics by the disability status. We also reported the prevalence of psychological distress and quality of life at the baseline, as well as perceived increase in loneliness during the pandemic, among people with and without disability. Regarding these frequency analyses presented above, we also presented the raw prevalence in which sample design is not considered.
We went on to analyze the changes in psychological distress between 2017 and 2020 among people with and without disability. Incident cases were those whose status changed from not psychologically distressed at the baseline to being psychologically distressed at the follow-up. Persistent cases were those individuals who were psychologically distressed both at the baseline and at the follow-up. Logistic regression models were applied to compare people with disability to those without in terms of the incidence or persistence of psychological distress when the demographic covariates were not (unadjusted model) or were controlled for (adjusted model). The adjusted persistence/incidence of psychological distress refers to the proportion of persisting/new cases with psychological distress, controlling for the influence of the demographic variables included in the analysis, while the unadjusted persistence/incidence refers to the crude proportion without controlling for demographics. In other words, the adjusted persistence/incidence does not depend on the effects of demographics-age, sex, living alone, working status, and education level-while the unadjusted persistence/ incidence may depend on these effects. The adjusted prevalence of the persistence or incidence of psychological distress for people with and without disability was estimated using the margins command [56].
We also analyzed the interaction effect between the age and disability, quality of life at the baseline and disability, and perceived increase in loneliness during the pandemic and disability on the incidence of psychological distress when the demographic covariates were controlled for. We report the odds ratio (OR) as a measure of association. Table 1 presents the prevalence of the disability and demographic data measured at the baseline. Approximately 27% of the persons included in the analysis reported disability in both years. As Table 1 shows, at the baseline people with disability reported psychological distress (21%) and a lower quality of life (17%) more often (p < .001) than those without (8% and 5%, respectively). People with disability (35%) also more often (p < .001) reported perceived increase in loneliness during the pandemic than those without (22%). Table 1 also presents the raw prevalence of disability and demographic characteristics in which sample design is not taken into account. Table 2 shows the changes in psychological distress between 2017 and 2020 for people with and without disability. As previously defined, the incidence of psychological distress refers to the probability of becoming psychologically distressed at the follow-up in 2020 among persons who were not psychologically distressed at the baseline in 2017. The incidence of psychological distress was significantly higher among people with disability (19%) than among those without (7%) when demographic covariates were controlled for in the adjusted model (Table 2). Thus, there was a significant difference in the adjusted incidence of psychological distress, in which the effects of demographics-age, sex, living alone, working status, and education level-were taken into account. The unadjusted results were quite similar to the adjusted results ( Table 2), indicating that the demographics did not have much effect on the results.

Incidence and persistence of psychological distress
The persistence of psychological distress refers to the probability of staying psychologically distressed at the follow-up in 2020 among persons who were psychologically distressed at the baseline in 2017. The persistence of psychological distress was significantly higher for people with disability (66%) than among those without (25%) when demographic covariates were controlled for (Table 2). Thus, there was a significant difference in the adjusted persistence of psychological distress when the effects of demographics were taken into account. The unadjusted results were quite similar to the adjusted results, indicating that the demographics did not have much influence on the results.

Moderators of the relationship between disability and the incidence of distress
The effects of disability (p < .001), age (p = .01), and the interaction effect between the age and disability (p = .01) for the incidence of psychological distress were all significant. The effect of age indicated that the incidence of psychological distress was higher among youngest people aged 18 to 39 (15%) in comparison to those aged 40 to 69 (7%) or those aged 70+ (7%; Table 3). The interaction analysis indicated that the incidence of psychological distress (32%) was highest among younger people with disability, aged 18 to 39 ( Table 4). The difference in the incidence of psychological distress between people with and without disability was also high among the oldest people aged 70+ (OR = 4.22). Notably, other demographic covariates except age were not significant moderators for this relationship.
The effects of disability (p = .003), quality of life at the baseline (p < .001), and the interaction effect between quality of life at the baseline and disability (p = .01) for the incidence of psychological distress were all significant. The effect of the quality of the life indicated that the incidence of psychological distress was lower for people with a high quality of the life at the baseline (5%) in comparison to those with a low (21%) or medium quality of the life (16%, Table 3). The interaction analysis indicated that the difference in the incidence of psychological distress between people with (38%) and without (16%) disability was significant only among those with a poor quality of life at the baseline ( Table 4).
The effects of disability (p < .001) and perceived increase in Weighted = sample design was taken into account in the analysis; unweighted = sample design was not taken into account in the analysis. a No disability in either 2017 or 2020. b Disability in both 2017 and 2020. c Measured at the baseline.

Table 2
The incidence and persistence of psychological distress between 2017 and 2020 among people with and without disability. loneliness during the pandemic (p < .001) were significant on the incidence of psychological distress, but we did not find a significant interaction effect between perceived increase in loneliness and disability (p = .24). The effect of perceived increase in loneliness indicated that the incidence of psychological distress was higher among those who reported perceived increase in loneliness during the pandemic (17%) in comparison to those who did not report it (7%; Table 3). The insignificant interaction effect indicated that people who reported perceived increase in loneliness during the COVID-19 pandemic had an increased risk of becoming psychologically distressed at the follow-up irrespective of their disability status.

Discussion
We found that the incidence of psychological distress over the threeyear period covering the first phases of the COVID-19 pandemic was higher among people with disability than among those without, while age and quality of life at the baseline moderated this effect.
Our study demonstrates that the incidence and persistence of psychological distress during a period including the first 1.5 years of the pandemic was higher among people with disability than among those without. These results extend the previous findings on the general population that mental health problems increased during the pandemic [2][3][4][5][6][7][8][9][10][11]. Our results complement previous findings that people with disability experienced more psychological distress before and during the COVID-19 pandemic than those without [12][13][14][15][16][17][18][19][20][21][22] and reported increased stress more often during the pandemic than those without [27]. Our follow-up study further found that people with disability were more vulnerable to becoming and remaining psychologically distressed than those without disability between the time before the pandemic and its second wave.
Previous studies have indicated that people with disability were more vulnerable to the negative effects of the pandemic (e.g., serious COVID-19, decreased financial situation, and social exclusion) than those without [17,18,[23][24][25][26], and thus they may be particularly vulnerable to becoming psychologically distressed during the pandemic. Our study demonstrates that people with disability who had a low quality of life at the baseline became psychologically distressed by the follow-up. Thus, a high quality of life protected people with disability from developing psychological distress during the pandemic. Our results contribute to previous findings on the general population that aspects of the quality of life are associated with psychological distress and its symptoms [29][30][31][32][33][34]. Notably, the previous evidence indicated that psychological distress may also predict a poor quality of life [57], while some follow-up studies have not found a connection in this direction [30,34]. Additionally, according to cognitive theory [58], a negative assessment of quality of life aspects (e.g. dissatisfaction with life and oneself, perceiving oneself as vulnerable and one's living place as dangerous [53]) can lead to symptoms of psychological distress. The negative experience of the quality-of-life is more common among people with disability than those without [35,36]; hence they may be more vulnerable to becoming distressed. We also found that people who reported perceived increase in loneliness during the COVID-19 pandemic were more prone to becoming psychologically distressed at the followup, irrespective of their disability status. These results complement previous findings that loneliness was associated with psychological distress among the general population during the pandemic [37][38][39]. Those who experienced loneliness during the pandemic may have little social support and may appraise the pandemic situation more negatively, and thus their psychological distress may have increased in stressful crisis situations [59,60].
We found that as many as 32% of younger people with disability, those aged 18 to 39, reported psychological distress during the pandemic, despite not having reported psychological distress before it. This adds to previous studies that show that in the general population young people particularly experienced psychological distress during the COVID-19 pandemic [3,8,40,41]. We found that young people with disability were even more vulnerable to psychological distress during the pandemic than other young people of the same age group. In particular, individuals under 40 may have become psychologically distressed due to closures and changes in education (e.g., remote online courses), the cancellation of social events, the absence of interpersonal communication and social contact, job loss, being sensitive to negative information, and uncertainty related to the COVID-19 pandemic [3,6,15,40,61,62]. This situation can be particularly challenging for people with disability, who may require support with their studies, find distance learning challenging, depend on social relationships, face challenges getting jobs, be sensitive to negative information related to Table 4 The incidence of psychological distress between 2017 and 2020 among people with and without disability stratified by age and quality of life. Adjusted for demographic covariates (sex, age, living alone, and education level, and working status); these covariates did not include age in the age model. OR = odds ratio; CI = confidence interval; ref. = reference group. Sample design was taken into account in the analyses. Adjusted for demographic covariates (sex, age, living alone, education level, and working status); these covariates did not include age in the age model. OR = odds ratio; CI = confidence interval; ref. = reference group. Sample design was taken into account in the analyses.
COVID-19, be more uncertain about COVID-19 because their disability may prevent them accessing information regarding the pandemic, and having to avoid social contacts because underlying health conditions may increase their risk of serious illness from COVID-19 [63][64][65][66][67]. We found that the difference in the incidence of psychological distress between people with and without disability was also high among people aged 70+, although younger people with disability had the highest incidence of psychological distress. Older people may become psychological distressed during the pandemic because they are at a higher risk of more serious illnesses associated with COVID-19 and may be vulnerable to restrictions and social isolation [51,68,69]. These vulnerabilities may be particularly high among older people with disability; therefore, they may be prone to becoming distressed during the pandemic.

Limitations and strengths
The main strength of this study is its follow-up setting, which was used to identify the association between disability and psychological distress. In addition, the nationally representative sample was utilized in the study, and weighting-constructed based on the register data-was used in the analyses to consider the sampling design and nonparticipation [42]. Therefore, the results represent the Finnish adult population. Regarding limitations, the response rate was lower in the follow-up, which may weaken the generalizability of the results for the entire population. However, in population surveys, a response rate about 40% is quite common [70,71], and in our data, both at the baseline and at the follow-up, the response rate was slightly higher. Another limitation of the study was that we used a complete case analysis to handle the missing data. However, weighting was used in the analyses to take nonparticipation into account. Weighting is useful in correcting unit nonresponse, and it also corrects the distribution of known background factors in the group of participants to match the distribution in the population [42,44]. Additionally, the study measured the effects of COVID-19 during its second wave, so there was no information on the effects of a prolonged pandemic.
We based our disability metrics on an internationally recognized method, the GALI tool, to identify individuals with disability [46,47]. One limitation of the study is that we used the single-item GALI tool, which refers to general restrictions in health-related activity without specifying the type of disability. We focused on those who had disability both at the baseline and the follow-up to understand psychological distress among individuals with permanent disability. Therefore, the prevalence of disability obtained in our study is not comparable with the prevalence from other surveys defined based on one measurement point. Based on other national surveys using the GALI tool, the prevalence of disability in Finland is over 30% [72,73]. We also used internationallyused instruments to assess people's psychological distress (MHI-5) and quality of the life (EUROHIS-QOL 8-item index). Previous studies have indicated that the convergent validity and internal consistency of the MHI-5 or EUROHIS-QOL 8-item index are good [48,52,74].

Conclusions
This study highlights that individuals with disability more often became psychologically distressed during the COVID-19 pandemic. Furthermore, we found that a low quality of life at the baseline among people with disability increased their vulnerability to becoming psychologically distressed later on. Our results underline the need for targeted support for people with disability. It is important to address the quality of life of people with disability in practical and supportive ways, such as providing help in daily activities and promoting physical and emotional well-being (direct support); enabling adequate physical and social activities, developing environments that meet their functional needs; improving the social acceptance of disability; and helping them to develop more positive self-appraisals [58,[75][76][77][78]. Our findings also highlight that perceived increase in loneliness during the COVID-19 pandemic increased the susceptibility of becoming psychologically distressed among the entire population. Thus, interventions targeting mental and psychological resilience in times of pandemics should also focus on reducing loneliness among people with and without disability.

Declaration of competing interest
The authors have no competing interests to report.