Sample Size for Estimation of G and Phi Coefficients in Generalizability Theory

WOS: 000319393600013Problem Statement: Reliability, which refers to the degree to which measurement results are free from measurement errors, as well as its estimation, is an important issue in psychometrics. Several methods for estimating reliability have been suggested by various theories in the field of psychometrics. One of these theories is the generalizability theory. In generalizability theory, two distinct reliability coefficients are estimated: the generalizability coefficient (G coefficient) for relative evaluation, and the index of dependability (Phi coefficient) for absolute decisions. Like in all methods of reliability estimation, G and Phi coefficients are estimated based on a data set obtained from a sample as a result of administering the instrument. Therefore, it has been a critical issue to determine what sample size is necessary in order to reliably estimate the population's characteristics. Purpose of Study: The purpose of this study is to determine the adequate sample size required to ensure that the G and Phi coefficients obtained from a sample can estimate the G and Phi coefficients for the population in an unbiased way. Methods: A total of 480691 students who took Form A of the SBS test for the 60, grade in 2008 were considered as the population of the study. Using a bootstrap method, a total of 1200 students were selected from this population, randomly falling into 12 subgroups consisting of different sample sizes (n=30, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000), with each sample size having 100 replications. Since the test battery contained five subtests with distinct contents and numbers of items, and all items were replied to by all participants, a p(square) x t(c) multivariate G theory design was used. G and Phi reliability coefficients were estimated both for the population and each of the 12 distinct samples of different sizes. The relative root mean square error (R-RMSE) index was used as the error index to analyze the consistency of the G and Phi coefficients with the G and Phi parameters estimated for the population. Findings and Results: It was found that the G and Phi coefficients estimated for a sample size of 30 tended to be less than the G and Phi parameters, and the R-RMSE value was greater than.01. When the sample size was 50 or more, R-RMSE values were less than.01. Thus it can be said that G and Phi coefficients are robust estimators of G and Phi parameters. Moreover, it was concluded that where the sample size is 400 or greater, R-RMSE values become stable. It was seen that a sample size of 400 is a more exact and robust estimator of G and Phi parameters, and increasing the sample size over 400 does not make a significant contribution to the unbiased estimation of G and Phi parameters. Conclusions and Recommendations: A sample size of 30 does not provide an adequately unbiased estimation of G and Phi coefficients. It can be recommended that sample sizes of 50 to 300 are adequate for a robust estimation of G and Phi coefficients; however, a more exact and robust estimation requires a sample size of 400. In future research, the sample size for facets using different designs of G theory can be studied

PISA 2015 Reading Test Item Parameters Across Language Groups: A measurement Invariance Study with Binary Variables

Large-scale international assessments, including PISA, might be useful for countries to receive feedback on their education systems. Measurement invariance studies are one of the active research areas for these assessments, especially cross-cultural and linguistic comparability have attracted attention. PISA questions are prepared in the English language, and students from many countries answer the translated form. In this respect, the purpose of our study is to investigate whether there is a measurement invariance problem across native English and non-native English speaker groups in the PISA-2015 reading skills subtest. The study sample included students from Canada, the USA, and the UK as the native speaker group and students from Japan, Thailand, and Turkey as the non-native speaker group. Measurement invariance studies taking into account the binary structure of the data set for these two groups revealed that eight of the twenty-eight items in the PISA-2015 reading skills test had possible limitations in equivalence

Deficit Irrigation Stabilizes Fruit Yield and Alters Leaf Macro and Micronutrient Concentration in Tomato Cultivation in Greenhouses: A Case Study in Turkey

Water is crucial for agriculture and needs to be used effectively due to climate change and drought in the Mediterranean region. For this reason, to adapt to water deficit scenarios, deficit irrigation applications are increasing in importance. The aim of this research was to determine the effect of varying levels of irrigation on growth parameters and concentration of nutrients in tomato plants grown under greenhouse conditions. The irrigation schedule used in this study was designed to include 100% (control), 90%, 80% and 70% of evaporation from the class-A pan. Water deficit was found to cause a stress effect in tomato plants, which was reflected in changes in the physiological function plants, such as flowering and early ripening. In addition, the SPAD values were examined, for which the lowest value of the green color intensity of the leaves was 47.3 (I3) and the highest was 48.7 (I4). However, the results of statistical analyses show that the difference was not significant. We also observed that the height values of tomato plants were the highest in the period of seedling and fruit ripening under full irrigation. Furthermore, analysis of the macronutrient content of tomato leaves showed that the obtained values were below the threshold values recommended for manganese. Based on these and similar studies, we believe that the application of water stress is most effective during the phases in which the plants are least affected. We believe that determining the periods during which tomato or any other crop is be affected by the least water stress will be more accurate for both plant development and economic production

A Preliminary Study to Evaluate the Reproducibility of Factor Analysis Results: The Case of Educational Research Journals in Turkey

In quantitative research, an attempt to reproduce previously reported results requires at least a transparent definition of the population, sampling method, and the analyses procedures used in the prior studies. Focusing on the articles published between 2010 and 2017 by the four prestigious educational research journals in Turkey, this study aimed to investigate the reproducibility of the factor analysis results from a theoretical perspective. A total of 275 articles were subject to descriptive content analysis. Results showed that 77.8% of the studies did not include an explicit definition of the population under interest, and in 50.9% of the studies, the sampling method was either not clear or reported to be convenience sampling. Moreover, information about the missing data or a missing data dealing technique was absent in the 76% of the articles. Approximately, half of the studies were found to have inadequate model fit. Furthermore, in almost all studies, it could not be determined whether the item types (i.e., levels of measurement scales) were taken into consideration during the analyses. In conclusion, the majority of the investigated factor analysis results were evaluated to be non-reproducible in practice

Intraosseous angiolipoma of the frontal bone with a unique location: A clinical and pathological case illustration and review of the literature

Here, we report a case of a 16-year-old female patient was referred with scalp swelling and headache. Her neurological examination was normal and imaging of the skull revealed a well-defined lytic lesion measuring 15 mm x 6 mm to the right of the frontal bone. She was operated on with a prediagnosis of Langerhans cell histiocytosis. A wide excision with negative margins was made and the defect was reconstructed with a titanium plate. Subsequently, the lesion was histopathologically diagnosed as an angiolipoma of the frontal bone. The postoperative period was uneventful and she remained well during 1-year follow-up with no evidence of recurrence. Angiolipomas are rare benign lipomatous lesions located mostly in subcutaneous tissue of the forearm or trunk and frequently occur before puberty or in young adults. They are not common in bones. To the best of our knowledge, this is the first angiolipoma of the frontal bone reported

Predicting aggression in children with ADHD

WOS: 000209640400014PubMed ID: 24860616Objective: The present study uses structural equation modeling of latent traits to examine the extent to which family factors, cognitive factors and perceptions of rejection in mother-child relations differentially correlate with aggression at home and at school. Methods: Data were collected from 476 school-age (7-15 years old) children with a diagnosis of ADHD who had previously shown different types of aggressive behavior, as well as from their parents and teachers. Structural equation modeling was used to examine the differential relationships between maternal rejection, family, cognitive factors and aggression in home and school settings. Results: Family factors influenced aggression reported at home (.68) and at school (.44); maternal rejection seems to be related to aggression at home (.21). Cognitive factors influenced aggression reported at school (.-05) and at home (-.12). Conclusions: Both genetic and environmental factors contribute to the development of aggressive behavior in ADHD. Identifying key risk factors will advance the development of appropriate clinical interventions and prevention strategies and will provide information to guide the targeting of resources to those children at highest risk