Users Online: 3040 Home Print this page Email this page Small font sizeDefault font sizeIncrease font size


Home About us Editorial board Search Ahead of print Current issue Archives Submit article Instructions Subscribe Contacts Login 

 Table of Contents  
Year : 2022  |  Volume : 66  |  Issue : 4  |  Page : 451-457  

Social isolation, social support, and psychological distress among the elderly during the COVID-19 pandemic: A cross-sectional study from central India

1 Assistant Professor, All India Institute of Medical Sciences, Nagpur, Maharashtra, India
2 Assistant Professor, Mahatma Gandhi Fuji Guruji Social Work Studies Centre, Wardha, Maharashtra, India
3 Professor, Department of Community Medicine, All India Institute of Medical Sciences, Nagpur, Maharashtra, India

Date of Submission04-Apr-2022
Date of Decision23-Jul-2022
Date of Acceptance23-Oct-2022
Date of Web Publication31-Dec-2022

Correspondence Address:
Pradeep Deshmukh
Department of Community Medicine, All India Institute of Medical Sciences, Nagpur - 441 108, Maharashtra
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijph.ijph_482_22

Rights and Permissions

Background: In the present COVID-19 pandemic, social distancing measures have been advised to protect elderly from infection which might have led to poor mental health state. Objective: A cross-sectional study was carried out to assess the magnitude of social isolation, social support, and psychological distress among the elderly during the COVID-19 pandemic in Central India. Methods: The estimated sample size was 1535. The sample was equally distributed among rural, semiurban, and urban strata of districts. Social isolation was measured using Lubben's Social Network Scale-Revised, and psychological distress was assessed using Kessler K10 Psychological Distress Scale. Other parameters such as a history of COVID-19 illness and COVID-19 vaccination were assessed. Results: The prevalence of social isolation was higher at 23.6% during the COVID-19 pandemic compared to before the pandemic period (15.0%). The majority perceived a high level of social support during the pandemic (55.3%) and 39.9% received moderate support. Overall, 18.4% of the respondents had psychological distress. Out of them, 56.2% had mild distress, 20.1% had moderate distress, and 23.7% had severe distress. Significant predictors of psychological distress were female gender, lower socioeconomic status, history of COVID-19 disease among the participants, social isolation, and lack of social support. Conclusion: Social isolation and lack of social support were significant predictors of psychological distress among the elderly during the pandemic.

Keywords: COVID-19, Kessler-10, Lubben's Social Network Scale, mental health, Multidimensional Scale of Perceived Social Support, pandemic, psychological distress, social connectedness, social isolation, social support

How to cite this article:
Sujiv A, Kalaiselvi S, Tiwari MK, Deshmukh P. Social isolation, social support, and psychological distress among the elderly during the COVID-19 pandemic: A cross-sectional study from central India. Indian J Public Health 2022;66:451-7

How to cite this URL:
Sujiv A, Kalaiselvi S, Tiwari MK, Deshmukh P. Social isolation, social support, and psychological distress among the elderly during the COVID-19 pandemic: A cross-sectional study from central India. Indian J Public Health [serial online] 2022 [cited 2023 Apr 1];66:451-7. Available from:

   Introduction Top

The COVID-19 pandemic has set an unprecedented situation in global health. As of 18th March 2022, there were six million deaths globally and 516,510 deaths in India.[1] The case fatality rate among the elderly was as high as 19.2%.[2] Risk of death increased 62 times for those in the age group 65 years and above.[3] The risk of all-cause mortality during the COVID-19 pandemic was 1.55 times higher in the 60–69 age group compared to that of 20–29 age group. The Ministry of Health and Family Welfare had issued guidelines to prevent infection among the elderly by adopting social distancing measures.[4] There was a recommendation for ensuring social connections through telephone or video calling. Following this advisory, many of the elderly would likely have adopted social isolation measures or imposed by their relatives. The elderly are already at a high risk of social isolation[5],[6] and depression. A population-based survey (BKPAI survey) reported social isolation during the prepandemic period to be 19.3% and 23.4% psychological distress among the elderly in India.[7],[8]

Social distancing measures adopted by family members may increase the level of social isolation during the pandemic period. A study in the US reported a high prevalence of social isolation (54%) among the elderly living in community centers.[9] A study in the UK reported worsening of mental health during the pandemic.[10] However, there is limited evidence from India on the effect of the COVID-19 pandemic on social isolation and mental distress in this high-risk group.

Hence, the present study was carried out to study the magnitude of social isolation, social support, and psychological distress among the elderly population of Central India. The determinants of psychological distress during the pandemic were evaluated.

   Materials and Methods Top

Study setting

The cross-sectional study was carried out in the Nagpur and Wardha districts of Maharashtra in Central India. The districts were purposively selected to include one relatively high burden (Nagpur) and relatively low burden area (Wardha) in terms of COVID-19.

Study participants

The inclusion criterion for study participation was individuals aged 60 years and above living in the selected study area for the past 3 months. The exclusion criteria were participants who could not be contacted after two visits to the household, individuals who are hospitalized/bedridden, and those suffering from severe hearing loss.

Sample size

Assuming the prevalence of social isolation among the elderly to be 20%,[7] a Type I error of 5%, and a relative precision of 10%, the sample size was estimated to be 1535.[11]


The sample size was distributed equally between the two districts. Each district was stratified into urban, semiurban, and rural strata. The sample size was divided equally among the three strata. From each stratum, one ward or village with high burden of cases was selected.

In the selected ward or village, households were sampled using the random walk method till the sample size is achieved. From each household, one participant was included in the study. If there were more than one eligible participant in the household, the selection was done using the Kish method.[12] During the data collection period, i.e., May–October 2021, a total of 1780 households were contacted of which 1535 consented to participate (response rate of 86%).

Study tools

A pretested semistructured questionnaire was used to collect the data. The questionnaire included sociodemographic profile of the study participants, past or present exposure to COVID-19 infection, history of COVID-19 infection, COVID-19 vaccination, adherence to social isolation and other protective measures, enrollment in social security schemes, and enrollment in a health insurance plan. Socioeconomic status (SES) was assessed using modified Prasad classification updated for 2021. The International Standard Classification of Education 2011 and the International Standard Classification of Occupations were used, respectively, to classify the education and occupation of study participants.[13],[14]

Social isolation among the elderly was assessed using Lubben's Social Network Scale (LSNS). The participants were interviewed for social connections before and during the pandemic.[15],[16] Perceived social support was measured using the Multidimensional Scale of Perceived Social Support (MSPSS).[17] Psychological distress was measured using Kessler (K10) scale.[18]

Study variables

The primary outcome variable was psychological distress. The independent variables were age, gender, SES, exposure to COVID-19, infection with COVID-19, adherence to social isolation measures, adherence to other protective measures, availing old-age pension, LSNS-R score, and MSPSS score.

Data collection

The approval of the Institute Ethics Committee was obtained (AIIMS NGP/IEC/Pharmac/2021/232); data were collected through house-to-house visits after obtaining written informed consent. The second visit was made if the respondent was not available at the time of the first visit.

Data analysis

The quantitative variables were summarized as median (interquartile range [IQR]) and categorical variables as proportions. For SES, the upper and upper-middle classes were merged as “upper class” and others were reclassified as “lower class” for assessing the association. Education level was recategorized as no formal education and completed at least primary education.

For the LSNS scale, those with a total score of 19 or below were categorized as those with perceived social isolation. For the MSPSS scale, a score of <3 was categorized as low support, a score of 3–5 was categorized as moderate support, and those with more than 5 were categorized as high social support.

A K10 cutoff score of 20 recommended for older adults was used to define the presence of psychological distress.[19] The association of sociodemographic variables, social isolation, and social support with the primary outcome variable was assessed using the Chi-square test.

The variables with the significant association in univariate analysis (P < 0.05) were included in multivariate analysis. Binomial regression with the log-link function was used to evaluate independent predictors for psychological distress. The effect estimates were presented as prevalence ratio (95% confidence interval [CI]).

   Results Top

Sociodemographic characteristics of study participants

A total of 1535 participants were included in the study. The median age (range) of the participants was 68 (60–101) years, and the majority of the participants were 'young old' (55%) belonging to the 60–69 years' age group. More than half of them did not complete their primary education (55.8%). The average number of children (IQR) per participant was 3 (2–4), but the median number of children living with them was 1. Before retirement, most of them worked in elementary occupations (65.1%) and 58% belonged to the middle and lower-middle class. Among them, 23.5% received old-age pension benefits [Table 1].
Table 1: Sociodemographic characteristics of study participants assessed for social isolation during the COVID-19 pandemic in Central India, 2021

Click here to view

Social distancing measures

Among the participants, one-fifth of them (20.3%) reported not traveling to other towns/cities during the pandemic. A total of 159 participants (10.3%) reported following at least one social distancing measures on their own without any instructions from family members. All elderly who opt to follow social distancing measures choose to stay in a separate room to avoid contact. Several participants (7.6%) reported that social distancing measures were imposed by the family members. Majority of them restricted their elderly parents to meet visitors at home and imposed that they stay in a separate room (88.8%).

COVID-19 infection among the participants

Among the participants (n = 1535), 9.1% (n = 140) had COVID-19 infection. Of the 140 respondents infected with COVID-19, 50.7% of them were hospitalized (n = 71). During hospitalization, the family members supported their elderly members by ensuring proper nutrition and frequent hospital visits/calls.

Overall, 14.9% of the elderly reported that one or more of the family members had a COVID-19 infection in the past. During the episode of COVID-19 infection, 9.7% of the households with COVID-19 infection imposed physical distancing measures on the elderly in the household.

Social isolation

The prevalence of social isolation was higher at 23.6% (95% CI: 21.5%–25.7%) during the COVID-19 pandemic when compared to before pandemic period (15.0% [95% CI: 13.3%–16.9%]).

The total LSNS score for 12 items was significantly lower during the COVID-19 pandemic when compared to a time before the onset of the COVID-19 pandemic. The same result was observed in both relatives and friends' subscale, but the magnitude was more pronounced in the friends' subscale [Figure 1].
Figure 1: Box and Whisker plot showing LSNS scores among the respondents before and during COVID-19 (n = 1535). LSNS: Lubben's Social Network Scale

Click here to view

Perceived social support

The majority perceived a high level of social support during the pandemic (55.3%), followed by moderate support (39.9%). The contribution of social support from significant other partners was high compared to family or friends. Among the domains, the support received was higher from significant others when compared to other domains.

Psychological distress

Overall, 18.4% (95% CI: 16.6%–20.5%) of the respondents were found to have psychological distress. Among those with psychological distress (n = 283), the majority were classified as mild disorder (56.2%), followed by severe (23.7%) and moderate disorder (20.1%).

Psychological distress and its association with study parameters

Among the variables, gender, education, type of housing, socioeconomic class, and COVID-19 positive history among family members or self were significantly associated with psychological distress [Table 2].
Table 2: Association of sociodemographic variables with psychological distress among elderly during the COVID-19 pandemic in Maharashtra, 2021 (n=1535)

Click here to view

Considering the significance of factor with psychological distress and collinearity, the following parameters were included in the final multivariate model: gender, socioeconomic class, history of COVID-19 among the participants, social isolation during the pandemic, and low social support. All the included parameters were significant predictors of psychological distress in the participants.

Those with moderate social support and those with low social support had 3.3 times and 6 times increased prevalence, respectively, as compared to those with high social support. Positive history of COVID-19 and presence of social isolation during the COVID-19 pandemic were associated with 85% and 83% increased prevalence, respectively. Women and those in lower socioeconomic class were associated with a 29% and 75% increase in the prevalence of psychological distress, respectively [Table 3].
Table 3: Multivariate analysis showing independent predictors of psychological distress among elderly during the COVID-19 pandemic

Click here to view

   Discussion Top

The current study from one of the highly COVID-19-affected Indian states had shown the high social isolation and psychological distress among the elderly. The prevalence of social isolation was higher at 23.6% during the COVID-19 pandemic when compared to before pandemic period 15.0%. Most of the respondents (95.2%) have received moderate-to-high social support during the COVID-19 pandemic. The contribution of social support from significant other partners was high when compared to family or friends. Psychological distress was found among 18.4%. Female gender, low socioeconomic class, history of COVID-19, presence of social isolation, and low perceived social support were important predictors of psychological distress.

Social isolation during COVID-19

The prevalence of social isolation was high during the COVID pandemic compared to prepandemic period. The difference was higher in the friends' subscale compared to the relatives' subscale.

The literature review showed different scales used for the assessment of social isolation in the elderly. The prevalence of social isolation was higher in the present study when compared to a nationally representative survey (23.6% vs. 19.3%) during the pre-COVID era.[7] However, the national survey used participation in four different domains of activities to judge social isolation. When comparing studies during the pandemic, social isolation in the present study was lower when compared to that reported among elderly living in US community,[9] i.e., 23.6% versus 40% during the pandemic. This is an expected difference since those living in elderly communities are expected to have higher social isolation than those living with their families. The difference in sociocultural context could be another attributing factor. Family ties in India are probably strong when compared to that of US.

Perceived social support during COVID-19

The perceived social support among the respondents was relatively high during the COVID-19 pandemic. We did not have a pre-COVID data for the study sample. We also could not find similar studies for comparison. However, 95% of them perceived moderate-to-high social support. Hence, we conclude that the perceived social support was high despite high level of social isolation. It is evident that during the pandemic, the significant other partner was a constant source of support when compared to family members or friends.

Psychological distress during the COVID-19 pandemic

In the present study, 18.4% of the respondents were found to have psychological distress. Psychological distress was lower in the present study when compared to that of the BKPAI survey,[8] which reported a prevalence of 23.4% during pre-COVID times in a nationally representative sample. Although the prevalence of psychological distress is expected to be higher because of the pandemic, it is slightly lower. The difference could be attributed to the use of a different scale (GHQ-12 scale) in the BKPAI survey.[8] The survey finding, while they represent the national average, may not truly reflect the local status.

Few studies evaluated psychological distress among the elderly during COVID-19. A study in New Zealand[20] reported a prevalence of 9.03% among the elderly based on an online survey during the first wave of COVID-19. The prevalence is quite low when compared to that of the present study despite using a lower cutoff used in the online survey.[20] However, the present study was conducted following a much severe second wave. Other attributing factors could be sociocultural differences and the mode of data collection.

The prevalence of psychological distress was high in the multicountry study reported by Rahman et al.:[21] 30.9% compared to 18.4% in the present study. One explanation for the result could be a lower k10 cutoff score of 15 used by Rahman et al. when compared to 20 in the present study.

Overall, the level of psychological distress among the elderly was lower than anticipated. This could be due to the interview being conducted following the second wave of the pandemic, when the restrictions were less when compared to the first wave. Other attributing factor could be that the resilience in the elderly is higher when compared to younger generations. In support of this argument, a declining trend of psychological distress was observed with increase in age during the COVID-19 pandemic in studies of Pierce et al.[10] (UK) and that of Rahman et al.[21]

Predictors of psychological distress during COVID-19

In the present study, female gender, socioeconomic class, history of COVID-19 among the participants, social isolation, and social support were significant predictors of psychological distress during COVID-19. Several studies[10],[21] reported the female gender as an independent predictor of psychological distress. Similarly, association with income was also observed.[10] Rahman et al. reported a significant association of psychological distress with a positive history of COVID-19.[21]

Although studies were lacking during the COVID-19 pandemic, the association between social isolation and mental health was observed in other studies during pre-COVID-19 era. Nigudkar et al. reported a significant association between low frequency of contact and depression among the elderly in Mumbai.[22] A longitudinal study by Santini et al. among the elderly in the USA concluded that social disconnectedness increased perceived isolation and which in turn increased the risk of depression.[5] Schwartz et al. reported a bidirectional association between social connectedness and mental health among European elderly using structural equation modeling.[23] Indu et al. in their qualitative study reported similar findings corroborating the association between loneliness and mental health.[24]

Among studies done during the COVID-19 era, Kotwal et al. reported that an increase in loneliness was associated with increased rates of depression and anxiety in the elderly.[9] Nair et al. reported a similar association between social connectedness and mental distress during COVID-19.[25]

The elderly cohort is often associated with life-course events like retirement and the loss of a partner. Both these life-course events are often associated with social isolation and low social support among the elderly. The data in the present study also show that among the different domains of social support, a large contribution is received from significant others.

Grolli et al. in their review reiterated that isolation and fear of COVID-19 could perpetuate a state of chronic stress by deregulation of the hypothalamic–pituitary axis and release of pro-inflammatory cytokines.[26] These pro-inflammatory cytokines could lead to neurodegeneration and depression.


The study could be subject to recall bias. LSNS was evaluated in a retro-pre form forcing the respondents to recall the events before the pandemic. Since the pre-COVID-19 period is generally perceived to be better, there could be a bias in the responses. The present study used a higher cutoff (20 or more) for the Kessler scale compared to other studies. This could have underestimated the prevalence of psychological distress in the present study. The study could have been subject to acquiescence bias, especially for the Kessler scale and MSPSS.

The sample was purposively selected to include geographical areas severely affected by COVID-19 in each district; the generalizability to less-affected areas may be limited. To limit this bias, a severely affected district and moderately affected district were included.

Strengths and limitations

The strength of the study included a relatively large sample size and stratified samples include urban, periurban, and rural areas. For social isolation among the elderly, a specific validated scale, i.e., LSNS, was used. Similarly, validated scales like the MSPSS and Kessler K10 scale were used to assess the psychological distress, respectively. Data collection was done using Epicollect v5.1, which helped in reducing item nonresponse and helped in checking for errors.

Since the study did not have a pre-COVID data collection point, it could not capture the trend in psychological distress and social support.


The current study has the following implications. First, as infectious disease pandemics are highly vulnerable for social isolation, there has to be a context specific preparedness plan to protect vulnerable like elderly while drafting the national advisories. Second, this study shows a significant socioeconomic gradient in the prevalence of psychological distress. There is an existing spiral of vulnerability in terms of elderly, poor socioeconomic status, and gender dimensions. In addition, the fear of naïve pandemics and unprecedented restrictions in social life also increases the risk of psychological distress. Hence, families with vulnerable like elderly and socio economically disadvantaged should be guided to keep the social ties strong in spite of needs for imposing social distancing measures during pandemic. Third, as the elderly who themselves/families had higher psychological distress, it indicates the health-care providers to emphasize social support measures during post-COVID follow-up visits.

   Conclusion Top

Social isolation increased significantly among the elderly due to the COVID-19 pandemic. This was partly due to self-imposed/family-imposed restrictions. The perceived social support was relatively higher during the pandemic. Social isolation, low social support, and COVID-19 infection were important predictors of psychological distress apart from known factors such as female gender and socioeconomic class.


The study was conducted with financial support from the Indian Council for Social Science Research (ICSSR) under the grant CVID/289/32/2020-21/ICSSR.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

WHO Coronavirus (COVID-19) Dashboard; 2022. Available from: [Last accessed on 2022 Mar 21].  Back to cited text no. 1
Wang L, He W, Yu X, Hu D, Bao M, Liu H, et al. Coronavirus disease 2019 in elderly patients: Characteristics and prognostic factors based on 4-week follow-up. J Infect 2020;80:639-45.  Back to cited text no. 2
Yanez ND, Weiss NS, Romand JA, Treggiari MM. COVID-19 mortality risk for older men and women. BMC Public Health 2020;20:1742.  Back to cited text no. 3
Health Advisory for Elderly Population of India during COVID19. New Delhi; 2020. Available from: Last accessed on 7th November 2022.  Back to cited text no. 4
Santini ZI, Jose PE, York Cornwell E, Koyanagi A, Nielsen L, Hinrichsen C, et al. Social disconnectedness, perceived isolation, and symptoms of depression and anxiety among older Americans (NSHAP): A longitudinal mediation analysis. Lancet Public Health 2020;5:e62-70.  Back to cited text no. 5
Gerst-Emerson K, Jayawardhana J. Loneliness as a public health issue: The impact of loneliness on health care utilization among older adults. Am J Public Health 2015;105:1013-9.  Back to cited text no. 6
Kotian DB, Mathews M, Parsekar SS, Nair S, Binu VS, Subba SH. Factors associated with social isolation among the older people in India. J Geriatr Psychiatry Neurol 2018;31:271-8.  Back to cited text no. 7
Muhammad T, Srivastava S, Sekher TV. Association of self-perceived income status with psychological distress and subjective well-being: A cross-sectional study among older adults in India. BMC Psychol 2021;9:82.  Back to cited text no. 8
Kotwal AA, Holt-Lunstad J, Newmark RL, Cenzer I, Smith AK, Covinsky KE, et al. Social isolation and loneliness among san francisco bay area older adults during the COVID-19 Shelter-in-Place Orders. J Am Geriatr Soc 2021;69:20-9.  Back to cited text no. 9
Pierce M, Hope H, Ford T, Hatch S, Hotopf M, John A, et al. Mental health before and during the COVID-19 pandemic: A longitudinal probability sample survey of the UK population. Lancet Psychiatry 2020;7:883-92.  Back to cited text no. 10
Dean A, Sullivan K, Soe M. OpenEpi: Open Source Epidemiologic Statistics for Public Health, Version 3.01; 2013. Available from: [Last accessed 2022 Mar 23].  Back to cited text no. 11
Kish L. A procedure for objective respondent selection within the household. J Am Stat Assoc 1949;44:380-7.  Back to cited text no. 12
UNESCO. International Standard Classification of Education ISCED 2011.Montreal: UNESCO Institute for Statistics; 2012. p. 64. Available from: [Last accessed on 2021 Feb 19].  Back to cited text no. 13
ISCO – International Standard Classification of Occupations. Available from: [Last accessed on 2019 Nov 04].  Back to cited text no. 14
Lubben JE. Assessing social networks among elderly populations. In: Family & Community Health: The Journal of Health Promotion & Maintenance. Vol. 11. US: Lippincott Williams & Wilkins; 1988. p. 42-52.  Back to cited text no. 15
Lubben J, Blozik E, Gillmann G, Iliffe S, von Renteln Kruse W, Beck JC, et al. Performance of an abbreviated version of the Lubben Social Network Scale among three European community-dwelling older adult populations. Gerontologist 2006;46:503-13.  Back to cited text no. 16
Kaur K, Beri N. Psychometric properties of multidimensional scale of perceived social support (MSPSS): Indian adaptation. Int J Sci Technol Res 2019;8:2796-801.  Back to cited text no. 17
Patel V, Araya R, Chowdhary N, King M, Kirkwood B, Nayak S, et al. Detecting common mental disorders in primary care in India: A comparison of five screening questionnaires. Psychol Med 2008;38:221-8.  Back to cited text no. 18
Vasiliadis HM, Chudzinski V, Gontijo-Guerra S, Préville M. Screening instruments for a population of older adults: The 10-item Kessler psychological distress scale (K10) and the 7-item generalized anxiety disorder scale (GAD-7). Psychiatry Res 2015;228:89-94.  Back to cited text no. 19
Every-Palmer S, Jenkins M, Gendall P, Hoek J, Beaglehole B, Bell C, et al. Psychological distress, anxiety, family violence, suicidality, and wellbeing in New Zealand during the COVID-19 lockdown: A cross-sectional study. PLoS One 2020;15:e0241658.  Back to cited text no. 20
Rahman MA, Islam SM, Tungpunkom P, Sultana F, Alif SM, Banik B, et al. COVID-19: Factors associated with psychological distress, fear, and coping strategies among community members across 17 countries. Global Health 2021;17:117.  Back to cited text no. 21
Nigudkar A, Wandrekar J, Sovani A, Thatte S. Social connectedness in ageing and its correlates: Emotional and cognitive health. Indian J Gerontol 2019;33:20-30.  Back to cited text no. 22
Schwartz E, Litwin H. The reciprocal relationship between social connectedness and mental health among older European adults: A SHARE-Based analysis. J Gerontol B Psychol Sci Soc Sci 2019;74:694-702.  Back to cited text no. 23
Indu P, Remadevi S, Philip S, Mathew T. A qualitative study on the mental health needs of elderly in Kerala, South India. J Geriatr Ment Heal 2021;5:143.  Back to cited text no. 24
Nair T, Appu AV. Social connectedness and psychological distress of elders during COVID-19. Indian J Gerontol 2021;35:200-12.  Back to cited text no. 25
Grolli RE, Mingoti ME, Bertollo AG, Luzardo AR, Quevedo J, Réus GZ, et al. Impact of COVID-19 in the mental health in elderly: Psychological and biological updates. Mol Neurobiol 2021;58:1905-16.  Back to cited text no. 26


  [Figure 1]

  [Table 1], [Table 2], [Table 3]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

  In this article
    Materials and Me...
    Article Figures
    Article Tables

 Article Access Statistics
    PDF Downloaded183    
    Comments [Add]    

Recommend this journal