Introduction We describe the development and initial validation of the telephone-administered cognitive test battery (TACT). We developed this battery as an assessment tool for the investigation of the genetic and environ- mental etiology of early cognitive decline in a large nationally representative cohort of 60-year-old twins and their siblings. It may, however, have a wide range of potential applications in gerontological epidemiolo- gy, genetic epidemiology and health-service evaluative research. Our project, ‘Cognitive Health and Aging in Twins and Siblings’ (CHATS), is currently in its pilot phase. Four hundred twin pairs, all born in 1938, were identified through their birth records and were traced and, where consent was given, interviewed. A later substantive study will involve 2000 twin pairs of the same age. We intend to measure cognitive status on three occasions: at baseline, and at two and four-and- a-half years thereafter. Two factors influenced our choice of assessment strategy. Firstly, subjects would be spread across the length and breadth of the United Kingdom. This, coupled with the need for multiple reassessments of cognitive status, would render face-to-face interview- ing unfeasibly expensive and logistically complex. Secondly, the incidence of overt dementia in the 60–65 age range is vanishingly low (Ott, Breteler, Van Harskamp, Stijnen and Hofman, 1998). Measurement of cognitive decline is a feasible alter- native, both as an important outcome in its own right, and because of what it may tell us about future risk of dementia. Cognitive decline is associated with a significant public health burden, as shown by strong associations with dependency (Gill, Richardson and Tinetti, 1995), morbidity (Weiler, Lubben and Chi, 1991; Binder and Robins, 1990) and mortality (Burns, Lewis, Jacoby and Levy, 1990). It is a core component 49 The development and initial validation of a telephone-administered cognitive test battery (TACT) MARTIN J. PRINCE, Department of Old Age Psychiatry, Institute of Psychiatry, London, UK, and Epidemiology Unit, London School of Hygiene and Tropical Medicine, London, UK ALISON M. MACDONALD, PAK C. SHAM, Section of Genetic Epidemiology and Statistics, Department of Psychological Medicine, Institute of Psychiatry, London, UK MARCUS RICHARDS, MRC National Survey of Health and Development, University College, London, UK SEEMA QURAISHI, ISOBEL HORN, Institute of Psychiatry, De Crespigny Park, London, UK ABSTRACT Telephone interviews are increasingly recognized as a convenient assessment tool for epidemiological studies with geographically scattered samples, particularly where repeated assessments are to be made. We have compiled a telephone- administered cognitive test battery (TACT) that aims to be sensitive enough to detect small but important degrees of early decline in cognitive function. The telephone-administered cognitive test battery comprises tests of crystallized intelligence, log- ical memory, visuo-spatial function, verbal fluency, and inductive reasoning. It incorporates a brief telephone assessment of cognitive status, the modified Telephone Interview for Cognitive Status (TICS-m), already validated as a screening test for dementia. We carried out a preliminary pilot study on 98 volunteer twin subjects. The test was generally administered in less than 30 minutes. Most component test scores were normally distributed with no evidence of ceiling or floor effects. We test- ed for the effects of age and education, and estimated test–retest reliability. A second-order factor analysis suggested that TACT measured three dimensions of cognitive function (1) logical memory, (2) crystallized intelligence and (3) the ability to learn and apply rules to abstract material under pressure of time. The last of these dimensions was the most influenced by age. The TACT is a convenient and efficient, yet comprehensive and demanding, measure of cognitive status with wide- ranging applications in gerontological epidemiology, genetic epidemiology and health service evaluative research. Key words: telephone interviews, cognitive function, genetic epidemiology, gerontology International Journal of Methods in Psychiatric Research, Volume 8, Number 1