Computer assisted telephone interview collected information about twin and family status, height, weight, education, occupation, alcohol, tobacco, caffeine, common illnesses, medications, and gender- and age-specific questions.

For twins aged 65 or older, a module aimed to identify dementia cases was added to the interview.

Information about maternal and birth characteristics were collected in participants' birth records.

SALT participants aged 65 or older were included in HARMONY and administered a screening instrument for dementia as part of the SALT interview. All twins who screened positive, together with their co-twins and a sample of cognitively intact controls, were referred to a clinical phase.

Information about participants' complete medical history, including use of prescription and non-prescription medications, as well as onset and sequence of memory and cognitive symptoms, was collected through medical records review and informant interview. Dementia diagnosis, including differential diagnosis, was then set at a multidisciplinary conference.

Cognitive screening was based on the twin’s performance on the TELE cognitive screening instrument, which incorporates the 10-item mental status questionnaire (MSQ), two other cognitive domains, and questions about health and daily functioning. For individuals who performed poorly on the TELE, an informant was interviewed with the Blessed Dementia Rating Scale (BDRS) about how much the twin’s cognitive status interfered with daily functioning.

Participants underwent a visit by an assessment team composed of a nurse and a physician, which included physical and neurological examination, a neuropsychological assessment; and referral for neuroimaging.

Blood was collected for laboratory tests.

The primary aim to the TwinGene project was to enhance the SALT study with biological specimens. Participants were asked to fill out a questionnaire about common diseases and to contact their local healthcare facility for health checkup. Subjects living in the vicinity of four largers cities were given the option of visiting hospital blood centers, in which case the health checkup was omitted.

Blood samples were also collected during this visit.

The SALTY project focused on the younger part of the SALT study born between 1943 and 1958. The data collection consisted of an extensive self-report paper-questionnaire and an Internet-based investigation that included questionnaires on musical experience, tendency to experience psychological flow and creative achievement, as well as test of cognitive and motor performance.

In addition, saliva was collected for DNA extraction.