This multicenter study conducted in several Portuguese institutions aims to compare the screening ability of the several Geriatric Depression Scale (GDS) validated versions for the Portuguese population (GDS-30, GDS-15, GDS-10 and GDS-5), as well as to establish their psychometric properties, using a large sample of elderly people with neurocognitive disorders attending social responses addressed to the elderly. Secondarily, cognitive state will be assessed.

Depression is the most common mental health problem among older people, both in Portugal and around the world. Due to the fast aging of the world population, depression is a significant problem, with an estimated prevalence between 8% and 16%, which is more common in institutionalized elderly. Several studies have shown the negative consequences of depression in the elderly, which has been associated with higher morbidity and mortality rates, increased use of health services and increased costs. In addition, older people's depression is associated with major disability, chronic health problems, higher suicide rates, dementia and a lower quality of life. However, it is often an unrecognized, and therefore untreated, problem.

Under these circumstances, screening people at risk of depression (people with chronic illness, stroke, dementia, institutionalized or attending social responses, etc.) is a strategy with potential to reduce the impact of depression among the elderly.

One of the most commonly used screening scales for depressive symptoms in elderly is the Geriatric Depression Scale (GDS), a widely known and widely used scale designed specifically for older people. For this reason, it does not include questions related to somatic symptoms, as they lack discriminatory value in older people, because they can be attributed to other physical conditions or the aging process. The original version of the scale is composed by 30 items with a dichotomous response (yes/no) assessing motivation, energy, past and future orientation, mood, cognitive complaints, anxiety and irritability. The GDS scale has good psychometric properties and has been evaluated in a wide range of geriatric populations, institutionalized patients, elderly with chronic health problems, people with dementia, etc. In order to achieve better time efficiency in its administration, the original 30-item scale was abbreviated to a 15-item version. Posteriorly, multiple shorter versions of this scale were developed, composed by one, four, five, ten or twelve items.

The GDS scale has been widely translated and validated worldwide. In Portugal, the GDS-30 was adapted and validated by Pocinho, Farate, Dias, Lee and Yesavage. The versions of GDS-15, GDS-10 and GDS-5 were adapted and validated by Apóstolo and colleagues having demonstrated good psychometric properties and, therefore, potential as a screening tool for depressive symptoms in older people.

The aim of this study is to compare the screening ability of the several validated versions for the Portuguese population of the GDS scale (GDS-30, GDS-15, GDS-10 and GDS-5), as well as to establish their psychometric properties, using a large sample of elderly patients attending social responses addressed to the elderly. This study will allow recommendations on which is the most sensitive GDS version for detecting depressive symptoms by comparing them with other depression screening scales.

To achieve this, the results of the several GDS versions will be compared with the application of a gold standard, the Beck-II Depression Inventory [BDI-II].

Regarding the BDI-II, it is important to mention its good psychometric characteristics when used in the elderly population, which were evident in studies that compared the psychometric characteristics of different scales used to assess depression in the elderly. I was concluded that this instrument obtained a test-retest value of 0.93, Cronbach's α ranged from 0.76 to 0.91 in elderly Americans, in a community-dwelling elderly, in Puerto Rican residents, in elderly with heart problems, and in women living in institutions for the elderly. In elderly clinical samples, Cronbach's α ranged from 0.89 to 0.92. BDI is significantly and positively correlated with CES-D (r = 0.69, p <0.001) and with GDS (r = 0.71, p <0.001). The clinical utility of BDI-II is proven and high because of its clinical sensitivity and consistency with the DSM-IV criteria. In addition, it identifies many depressive symptoms and is one of the most commonly used instruments in the elderly without cognitive decline and also in non-clinical samples, as it is brief and easily administered and scored.

On the other hand, in another study where BDI-II was applied to elderly people with cognitive deficits, it was found that this population has symptoms similar to those of young people and adults, supporting the validity of this instrument in this population.

In order to reinforce the assessment of the screening ability of the several GDS versions validated for the Portuguese population, as well as to establish their psychometric properties, a sample (estimated at about 25%) will be defined, in which the GDS will be compared with a gold standard, that will consist of a semi-structured interview guide based on the criteria of the Diagnostic and Statistical Manual of Mental Disorders (5th ed.) for depressive disorders. For this sample, a questionnaire will be answered by the professionals who perform the evaluation, regarding their opinion about which GDS version is more easily understandable by the participants and the participants' preference regarding the different versions of GDS, as a means of assessing which version is more discernible for the participants. All the GDS versions validated for the Portuguese population (GDS-30, GDS-15, GDS-10 and GDS-5) will be administered to these participants.

Inclusion Criteria:

• Having a diagnosis of neurocognitive disorder according to the DSM-5 criteria and based on the MMSE scores.
• To be able to understand and answer the instruments' questions.
• Being 65 years of age or older.
• Being a native Portuguese speaker.
• To attend a social response addressed to the elderly in an institution.

Exclusion Criteria:

• Having severe sensory and physical limitations, severe disconnection from the environment, or presence of severe neuropsychiatric symptoms that make it impossible to administer the assessment battery.

In each participanting institution, users who meet the inclusion criteria will be selected to answer the assessment instruments. Prior to the inclusion in the study, informed consent will be obtained from participants or their caregivers after they have received information about the study. This information will include the purpose of the study, the data processing in accordance with current legislation, the voluntary nature of the participation in the study and the right to withdraw consent at any time without affecting the services received in the institution.