This study presents a general framework for single-administration reliability methods, such as Cronbach's alpha, Guttman's lambda-2, and method MS. This general framework was used to derive a new approach to estimating test-score reliability by means of the unrestricted latent class model. This new approach is the latent class reliability coefficient (LCRC). Unlike other single-administration reliability methods, LCRC places few restrictions on the item scores. A simulation study showed that if data are multidimensional or if double monotonicity does not hold, then LCRC is less biased relative to the true reliability than Cronbach's alpha, Guttman's lambda-2, method MS, and the split-half reliability coefficient.Test-score reliability, denoted r XX 0 , is one of the most reported statistics in social and behavioral science research. This study adopts the definition proposed by Lord and Novick (1968, p. 61). Let X be the test score, which is defined as the sum of the J item scores X j ðj ¼ 1; . . . ; J Þ, so that X ¼ P J j¼1 X j . In the population, test score X has expectation m X and variance s 2 X . Let T be the unobservable true score (Lord & Novick, 1968, chaps. 2 and 3), defined as a testee's expectation of X across his or her propensity distribution of independent test repetitions. In the population, T has expectation m T and variance s 2 T . Test-score reliability is defined as the product-moment correlation between two sets of independent test scores from two different but interchangeable tests known as parallel tests (which replace two independent repetitions), and equals the ratio of true score and test score variances,Article