Multiple-group IRT models in Stata
IRT models explore the relationship between a latent (unobserved) trait and items that measure aspects of the trait. This often arises in standardized testing where the trait of interest is ability, such as mathematical ability. A set of items (test questions) is designed, and the responses measure this unobserved trait. Researchers in education, psychology, and health frequently fit IRT models.
Stata’s irt commands fit 1-, 2-, and 3-parameter logistic models. They also fit graded response, nominal response, partial credit, and rating scale models, and any combination of them. And after fitting a model, irtgraph graphs item-characteristic curves, test characteristic curves, item information functions, and test information functions.
New in Stata 16, the irt commands allow comparisons across groups. Take any of the existing irt commands, add a group(varname) option, and fit the corresponding multiple-group model. For instance, type
. irt 2pl item1-item10, group(female)
and fit a two-group 2PL model.
Group-specific means and variances of the latent trait will be estimated. Group-specific difficulty and discrimination parameters can also be estimated for one or more items. With constraints, you can specify exactly which parameters are allowed to vary and which parameters are constrained to be equal across groups.
You can even use likelihood-ratio tests to compare models with and without constraints to perform an IRT model-based test of differential item functioning.
Stata 16 has a new suite of commands for performing meta-analysis. This suite lets you explore and combine the results from different studies. For instance, if you have collected results from 20 studies about the effect of a particular drug on blood pressure, you can summarize these studies and estimate the overall effect using meta-analysis.
The new meta suite is broad, but what sets it apart is its simplicity.
You can type, for instance,
. meta set effectsize stderr
to declare precomputed effect sizes or use meta esize to compute effects from summary data. With this, you can perform random-effects, fixed-effects, or common-effect meta-analysis.
To estimate an overall effect size and its confidence interval, obtain heterogeneity statistics, and more, you simply type
. meta summarize
And visualizing the results is as easy as typing
. meta forestplot
But the meta suite provides much more.
Meta-regression and subgroup analysis allow you to evaluate the heterogeneity of studies. These are available via meta regress and meta forestplot, subgroup() or meta summarize, subgroup().
You can investigate potential publication bias. Check visually for funnel-plot asymmetry using meta funnelplot; formally test for funnel-plot asymmetry using meta bias; and assess publication bias using the trim-and-fill method with meta trimfill.
You can even perform cumulative meta-analysis with meta summarize, cumulative().
All the meta-analysis features are documented in the new Meta-analysis Reference Manual.
Stata 数据管理统计绘图软件
快速,简单并易于使用
点击式的界面和强大,直观的命令语言让Stata使用起来快速,精确并易于使用。
所有的分析结果都可以被复制和存档，并用来出版和审查。不管您什么时候写的内容，版本控制系统确保统计程序可
继续生成同样的结果。
统计功能介绍
Stata使得大量的统计工具用于指尖
● 基本表格和总结
● 案例对照分析
● ARIMA
● ANOVA 和MANOVA
● 线性回归
● 时间序列平滑
● 多层模型
● 生存分析
● 动态面板数据回归
● 结构方程建模
● 二进制，计数和审查结果
● ARCH
■ 标准方法，如■ 高级方法，如
● 多重替代法
● 调查数据
● Treatment effects
● 精确统计
● 贝叶斯分析
● ……
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