A Flexible Method for Diagnostic Accuracy with Biomarker Measurement Error.

Diagnostic biomarkers are often measured with errors due to imperfect lab conditions or analytic variability of the assay. The ability of a diagnostic biomarker to discriminate between cases and controls is often measured by the area under the receiver operating characteristic curve (AUC), sensitivity, specificity, among others. Ignoring measurement error can cause biased estimation of a diagnostic accuracy measure, which results in misleading interpretation of the efficacy of a diagnostic biomarker. Existing assays available are either research grade or clinical grade. Research assays are cost effective, often multiplex, but they may be associated with moderate measurement errors leading to poorer diagnostic performance. In comparison, clinical assays may provide better diagnostic ability, but with higher cost since they are usually developed by industry. Correction for attenuation methods are often valid when biomarkers are from a normal distribution, but may be biased with skewed biomarkers. In this paper, we develop a flexible method based on skew-normal biomarker distributions to correct for bias in estimating diagnostic performance measures including AUC, sensitivity, and specificity. Finite sample performance of the proposed method is examined via extensive simulation studies. The methods are applied to a pancreatic cancer biomarker study.

Item-Score Reliability in Empirical-Data Sets and Its Relationship With Other Item Indices.

Reliability is usually estimated for a total score, but it can also be estimated for item scores. Item-score reliability can be useful to assess the repeatability of an individual item score in a group. Three methods to estimate item-score reliability are discussed, known as method MS, method λ 6 , and method CA. The item-score reliability methods are compared with four well-known and widely accepted item indices, which are the item-rest correlation, the item-factor loading, the item scalability, and the item discrimination. Realistic values for item-score reliability in empirical-data sets are monitored to obtain an impression of the values to be expected in other empirical-data sets. The relation between the three item-score reliability methods and the four well-known item indices are investigated. Tentatively, a minimum value for the item-score reliability methods to be used in item analysis is recommended.

Methods for Estimating Item-Score Reliability.

Reliability is usually estimated for a test score, but it can also be estimated for item scores. Item-score reliability can be useful to assess the item's contribution to the test score's reliability, for identifying unreliable scores in aberrant item-score patterns in person-fit analysis, and for selecting the most reliable item from a test to use as a single-item measure. Four methods were discussed for estimating item-score reliability: the Molenaar-Sijtsma method (method MS), Guttman's method λ6 , the latent class reliability coefficient (method LCRC), and the correction for attenuation (method CA). A simulation study was used to compare the methods with respect to median bias, variability (interquartile range [IQR]), and percentage of outliers. The simulation study consisted of six conditions: standard, polytomous items, unequal α parameters, two-dimensional data, long test, and small sample size. Methods MS and CA were the most accurate. Method LCRC showed almost unbiased results, but large variability. Method λ6 consistently underestimated item-score reliabilty, but showed a smaller IQR than the other methods.

Item-Score Reliability as a Selection Tool in Test Construction.

This study investigates the usefulness of item-score reliability as a criterion for item selection in test construction. Methods MS, λ6, and CA were investigated as item-assessment methods in item selection and compared to the corrected item-total correlation, which was used as a benchmark. An ideal ordering to add items to the test (bottom-up procedure) or omit items from the test (top-down procedure) was defined based on the population test-score reliability. The orderings the four item-assessment methods produced in samples were compared to the ideal ordering, and the degree of resemblance was expressed by means of Kendall's τ. To investigate the concordance of the orderings across 1,000 replicated samples, Kendall's W was computed for each item-assessment method. The results showed that for both the bottom-up and the top-down procedures, item-assessment method CA and the corrected item-total correlation most closely resembled the ideal ordering. Generally, all item assessment methods resembled the ideal ordering better, and concordance of the orderings was greater, for larger sample sizes, and greater variance of the item discrimination parameters.

Indicações da validade convergente do teste Não-Verbal de Inteligência Son-R 2½-7[A] / Indications of the convergent validaty of the Non-verbal Tes of Intelligence Son-R 2½-7[A]

O objetivo deste estudo foi avaliar a validade convergente do teste não-verbal de inteligência SON-R 2½-7[a] no Brasil. O teste em questão é a versão abreviada do SON-R 2½-7 que foi publicado na Holanda em 1998 e que foi normatizado e validado em vários países de Europa. A versão abreviada foi administrada no Brasil em 120 crianças com idade variando entre 5 e 7 anos junto com as Matrizes Progressivas Coloridas (MPC) do Raven e com a Escala de Maturidade Mental Colúmbia (EMMC). A correlação, corrigida para atenuação, do SON-R 2½-7[a] com estes dois testes foi respectivamente, 0,77, e 0,62. Foi observada uma relação particularmente forte entre o MPC e a escala de execução do SON-R 2½-7[a], e entre o EMMC e a escala de raciocínio do SON-R 2½-7[a]. Os resultados do presente estudo indicam uma boa validade convergente do teste para a faixa de idade investigada.

This study aimed to investigate the convergent validity of the nonverbal test of intelligence SON-R 2½-7[a] in Brazil. This test is the abridged edition of the SON-R 2½-7 nonverbal test of intelligence that was published in 1998 in The Netherlands with normatization and validation studies realized in various European countries. The abridged edition was administered in Brazil to 120 children with ages varying between 5 and 7 years together with Raven’s Colored Progressive Matrices (CPM) and the Columbia Mental Maturity Scale (EMMC). The correlation, corrected for attenuation, of the SON-R 2½-7[a] with these two tests was .77 and .62, respectively. A particularly strong relationship was observed between the CPM and the performance scale of the SON-R 2½-7[a], and between the EMMC and the SON-R reasoning scale. The results of this study indicate a fair convergent validity of the SON-R 2½-7[a] for the investigated age group.

Indicações da validade convergente do teste Não-Verbal de Inteligência Son-R 2½-7[A] / Indications of the convergent validity of the non-verbal test of intelligence Son-R 2½-7[A]

O objetivo deste estudo foi avaliar a validade convergente do teste não-verbal de inteligência SON-R 2½-7[a] no Brasil. O teste em questão é a versão abreviada do SON-R 2½-7 que foi publicado na Holanda em 1998 e que foi normatizado e validado em vários países de Europa. A versão abreviada foi administrada no Brasil em 120 crianças com idade variando entre 5 e 7 anos junto com as Matrizes Progressivas Coloridas (MPC) do Raven e com a Escala de Maturidade Mental Colúmbia (EMMC). A correlação, corrigida para atenuação, do SON-R 2½-7[a] com estes dois testes foi respectivamente, 0,77, e 0,62. Foi observada uma relação particularmente forte entre o MPC e a escala de execução do SON-R 2½-7[a], e entre o EMMC e a escala de raciocínio do SON-R 2½-7[a]. Os resultados do presente estudo indicam uma boa validade convergente do teste para a faixa de idade investigada.(AU)

This study aimed to investigate the convergent validity of the nonverbal test of intelligence SON-R 2½-7[a] in Brazil. This test is the abridged edition of the SON-R 2½-7 nonverbal test of intelligence that was published in 1998 in The Netherlands with normatization and validation studies realized in various European countries. The abridged edition was administered in Brazil to 120 children with ages varying between 5 and 7 years together with Raven's Colored Progressive Matrices (CPM) and the Columbia Mental Maturity Scale (EMMC). The correlation, corrected for attenuation, of the SON-R 2½-7[a] with these two tests was .77 and .62, respectively. A particularly strong relationship was observed between the CPM and the performance scale of the SON-R 2½-7[a], and between the EMMC and the SON-R reasoning scale. The results of this study indicate a fair convergent validity of the SON-R 2½-7[a] for the investigated age group.(AU)

Additive Partial Linear Models with Measurement Errors.

We consider statistical inference for additive partial linear models when the linear covariate is measured with error. We propose attenuation-to-correction and SIMEX estimators of the parameter of interest. It is shown that the first resulting estimator is asymptotically normal and requires no undersmoothing. This is an advantage of our estimator over existing backfitting-based estimators for semiparametric additive models which require undersmoothing of the nonparametric component in order for the estimator of the parametric component be root-n consistent. This feature stems from a decrease of the bias of the resulting estimator which is appropriately derived using a profile procedure. A similar characteristic in semiparametric partially linear models was obtained by Wang et al. (2005). We also discuss the asymptotics of the proposed SIMEX approach. Finite-sample performance of the proposed estimators is assessed by simulation experiments. The proposed methods are applied to a dataset from a semen study.