2.1 Data Source
This study has primarily utilized the Longitudinal Aging Study in India (LASI) Wave-1 data, which analyses the health, demographic and socio-economic nuances of the phenomenon of population ageing systematically. The survey was carried out in 30 states and six union territories of the country and has a sample size of 72,250 adults aged 45 years and above and their spouses irrespective of their age. A multi-stage stratified area-probability cluster sampling design with sub-districts/tehsils as primary sampling units (PSU) and village/urban wards as secondary sampling units (SSU) was used to collect the data. The detailed information about sampling design, fieldwork, data collection tools and processing etc. are available elsewhere24,25. The current study analysed information from older adults age 60 and above.
The study did not require any ethical approval as publicly available secondary data source from a longitudinal study was utilised. LASI wave-1 has adhered to all the standard procedures and approved protocols, including informed consent to collect data from the participants.
2.2 Variable Description
2.2.1 Outcome Variable
Undiagnosed depression
Older adults (60+) are defined as having depressive symptoms if they secure a score of four or more on a 0-10 score based CES-D scale. A score of three or more on a 0-7 CIDI-SF scale is defined as probable major depression among the older adults. Those individuals who fulfil both these criteria simultaneously are defined as the older adults who are measured depressed on both the scales of measurement. An older adult is defined as undiagnosed for depression on CIDI-SF or combined scale (CIDI-SF & CES-D) if he/she/they are measured as having depression on the respective scale and answered “no” to the question on self-reporting of ever diagnosed depression, where they have ever been told by a health professional as depressed. The estimation based on combined scale shows severe cases of undiagnosed depression.
2.2.2 Predictor variables
The study extracted data on certain background characteristics, such as urban-rural residence, sex (male, female), marital status (currently married, widowed, divorced/separated/deserted/others), living arrangement (living alone, living with spouse and/or others, living with spouse and children, living with children and others, and living with others), religion (Hindu, Muslim, Others), Caste/Tribe (Scheduled Castes, Scheduled Tribes, Other Backward Class, Others), educational attainment (no schooling, less than 5-years completed, 5-9 years completed, more than 10 years completed), work status (currently working, worked in the past but currently not working, never worked), monthly per capita expenditure (MPCE) quintile (poorest, poorer, middle, richer, richest), and geographic region of residence (North, Central, East, North-East, West and South India).
Other predictor variables, such as health insurance coverage, any other diagnosed neurological/psychiatric issues except depression, any physical disability, family history of Alzheimer’s/Parkinson’s disease/psychotic disorder, self-rated health (good/moderate/poor) and life satisfaction (low, medium, high), were also included in the statistical analysis.
2.3 Data analysis
The study analysed the prevalence of undiagnosed depression among older adults with respect to multiple socio-economic, demographic, residence-related, and other predictors using cross-tabulation analysis. Two multivariable logistic regression models, one for the CIDI-SF and second for the combined scale, were estimated to delineate the factors associated with the outcome of interest. We carried out all analyses by utilising the survey weights given in LASI Wave 1 to ensure the nationally representative nature of the sample. All the analyses were done using STATA 15.0 (Stata Corp., College Station, USA) software.