Estimating major sources of measurement error in individual intelligences scales: Taking our heads out of the sand

Four ubiquitous major sources of measurement error for individual intelligence scales were identified and discussed. It was argued that where these sources cannot be directly investigated, they should be estimated rather than ignored. The typical magnitude of error arising from each of content sampling, time sampling, scoring, and administration was estimated; their composite was found to produce a far larger standard error of measurement than manuals of individual intelligence tests typically report. Implications for practitioners are discussed.