naa a22 4500 510777171 CHVBK 20180411083234.0 cr unu---uuuuu 180411e20131201xx s 000 0 eng 10.3758/s13428-013-0320-7 doi (NATIONALLICENCE)springer-10.3758/s13428-013-0320-7 Shieh G. Department of Management Science, National Chiao Tung University, 1001 Ta Hsueh Road, 30050, Hsinchu, Taiwan aut Confidence intervals and sample size calculations for the standardized mean difference effect size between two normal populations under heteroscedasticity [Elektronische Daten] [G. Shieh] The use of effect sizes and associated confidence intervals in all empirical research has been strongly emphasized by journal publication guidelines. To help advance theory and practice in the social sciences, this article describes an improved procedure for constructing confidence intervals of the standardized mean difference effect size between two independent normal populations with unknown and possibly unequal variances. The presented approach has advantages over the existing formula in both theoretical justification and computational simplicity. In addition, simulation results show that the suggested one- and two-sided confidence intervals are more accurate in achieving the nominal coverage probability. The proposed estimation method provides a feasible alternative to the most commonly used measure of Cohen's d and the corresponding interval procedure when the assumption of homogeneous variances is not tenable. To further improve the potential applicability of the suggested methodology, the sample size procedures for precise interval estimation of the standardized mean difference are also delineated. The desired precision of a confidence interval is assessed with respect to the control of expected width and to the assurance probability of interval width within a designated value. Supplementary computer programs are developed to aid in the usefulness and implementation of the introduced techniques. Psychonomic Society, Inc., 2013 Behrens-Fisher problem nationallicence Cohen's d nationallicence Confidence interval nationallicence Precision nationallicence Welch's statistic nationallicence Behavior Research Methods Springer US; http://www.springer-ny.com 45/4(2013-12-01), 955-967 45:4<955 2013 45 13428 https://doi.org/10.3758/s13428-013-0320-7 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.3758/s13428-013-0320-7 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Shieh G. Department of Management Science, National Chiao Tung University, 1001 Ta Hsueh Road, 30050, Hsinchu, Taiwan aut NATIONALLICENCE 773 0- Behavior Research Methods Springer US; http://www.springer-ny.com 45/4(2013-12-01), 955-967 45:4<955 2013 45 13428 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer