Both commands only work for lower case variable names.
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This is ambiguous: To which commands to you refer to? Using your data (which has upper case letters) works with -omega- and with -omega2-. -
Dear Dirk: as you may notice the responses from Joseph and Brian, it seems that -omega- and -omega2- do not work if one has variable names starting with a capital letter. After I renamed the variables, I no longer saw the Stata error message.Originally posted by Dirk Enzmann View PostComment
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Hello! Sorry for busting out this old thread, but does anyone know if this version of -omega2- command could calculate the omega coefficient between two items? I replicated the code successfully with three items (many thanks to Dr. Enzmann for the code!) but when it comes to two items, an error message popped up saying that "convergence not achieved". I'm assuming this is because the code is based on the -sem- function, but would there be any alternatives for omega between two items? Thanks in advance!Comment
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A factor model with only two items is underidentified -- you would need to constrain the two loadings to be equal in order to identify it, hence the program will not work with only two items.Comment
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Thank you, Dr. Enzmann, for your response! That's exactly what I thought, but since I also saw journal articles examining 2-item dimensions with omega coefficients (using, for example, the -psych- package in R, as mentioned in this article), I was wondering if it is possible to find a Stata equivalent. Anyway, thanks again for your answer!Originally posted by Dirk Enzmann View PostComment
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Does -omega- and -omega2- be deleted from SSC?
Code:. ssc describe omega ssc describe: "omega" not found at SSC, type search omega (To find all packages at SSC that start with o, type ssc describe o) r(601); . ssc describe omega2 ssc describe: "omega2" not found at SSC, type search omega2 (To find all packages at SSC that start with o, type ssc describe o) r(601); . ssc describe omegacoef ------------------------------------------------------------------------------------------------ package omegacoef from http://fmwww.bc.edu/repec/bocode/o ------------------------------------------------------------------------------------------------ TITLE 'OMEGACOEF': module to calculate the omega reliability coefficient DESCRIPTION/AUTHOR(S) -omegacoef- calculates McDonald’s omega to estimate scale reliability. Omega has many desirable statistical properties that make it preferable to the widely used Cronbach’s alpha. KW: omega KW: alpha KW: reliability KW: psychometrics Requires: Stata version 12 Distribution-Date: 20210909 Author: Brian Shaw, Indiana University Support: email [email protected] INSTALLATION FILES (type net install omegacoef) omegacoef.ado omegacoef.sthlp ------------------------------------------------------------------------------------------------ (type ssc install omegacoef to install)Comment
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Not all community contributed programs are found at SSC. While I do not find any -omega- command, running -search omega- leads to a pointer to -omega2- on the UCLA statistics website. Run -search omega- and scroll down to find:
Click on the link (which will be blue in the Viewer) to get to a page from which you can install it.Code:omega2 from https://stats.oarc.ucla.edu/stat/stata/ado/analysis omega2. Program to compute omega squared after an ANOVA / Philip B. Ender / Statistical Computing and Consulting / UCLA Office of Academic Computing / [email protected] / STATA ado and hlp files in the package / distribution-date: 20071120Comment
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You can also use the command shown below to get a list of all user-written Stata packages by the UCLA ATS folks.
Here is the output. In the Stata output window, the package names will have hyperlinks, of course.Code:. // Get list of user-written packages from UCLA . net from https://stats.oarc.ucla.edu/stat/stata/ado/analysis
Code:---------------------------------------------------------------------------------------------------------------------------------------- https://stats.oarc.ucla.edu/stat/stata/ado/analysis/ Welcome to UCLA Academic Technology Services Stata programs. ---------------------------------------------------------------------------------------------------------------------------------------- These programs include tools for data analysis. These include programs from the Stata Technical Bulletin, courtesy of, and copyright, Stata Corporation. For more information about these programs, see our web page at http://www.ats.ucla.edu/stat/stata/ DIRECTORIES you could -net cd- to: .. Back to Main Directory PACKAGES you could -net describe-: ^ANOVA Tools^ anovalator main effects, two-way interactions, pairwise comparisons, linear contrasts (V11) ctems Cornfield-Tukey expected mean squares cellgr Cell histograms for factorial anova anovacontrast Computes contrasts in anova parcord2 Parallel coordinate plots effectsize Computes effect size after anova factorialsim Power and robustness simulation for two-way factorial anova designs fhcomp Fisher-Hayter pairwise comparisons fpower Anova power analysis fstar F* test for test of equal means nonadd Tukey test for nonadditivity omega2 Computes omega squared after an ANOVA qsturng Quantiles of the Studentized Range simanova Simulation for ANOVA simpower Power simulation for ANOVA smecriticalvalue Computes critical values for tests of simple main effects and related tests. sme Computes tests of simple main effects testalterr Computes anova F-ratio using arbitrary numeric error term. tukeyhsd Tukey's HSD pairwise comparisons tkcomp Tukey-Kramer pairwise comparisons tukeykramer Tukey-Kramer pairwise comparisons on lsmeans (emmeans) wtest W test for test of equal means ^Correlation and Regression Tools^ aipe Accuracy in parameter estimation canred Canonical correlation redundancy analysis (V9) collin Collinearity diagnostics fapara Factor analysis parallel analysis facom Communalities after factor analysis hadiplot Potential versus Residul Plot and Hadi influence measure hinflu6 Computes Hadi measure of regression influence lvr2dplot Leverage vs. Residual Squared with Cook's D ml_mediation Mediation with multilevel data partcorr Partial & semipartial correlation pathreg Path analysis using ols regression powerreg Power analysis for linear regression models protab Predicted proportions following logit transformation regeffectsize Computes effects size for variables in regression model regvalidate Postestimation command to perform validation thru resampling regfungible Postimation command to generate fungible regression weights resboot_mediation Mediation analysis with residual bootstrap rregfit R2 and fit indices for robust regression (rreg) rsquare Compute rsquare for all possible regressions sgmediation Sobel-Goodman mediation tests test2 Alternative test after regress wls0 Weighted least squares regression a la Greene ^Logistic, Poisson, Negative Binomial Regression Tools^ binary_mediation Mediation with binary mediator and/or binary response variable ldev Compute deviance after logistic ldfbeta Compute dfBeta in logistic regression logsub Logistic regression subsets nbvargr Graphs observed, poisson, & negative binomial probabilities powerlog Power analysis for logistic regression predcalc Predicted values calculated from linear & logistic regrs. scatlog scatterplot and logistic regression line vibl Visualizing Main Effects and Interactions for Binary Logit Models ^Graphics Tools^ histbox Histogram with boxplot meansdplot Plot means and standard deviations for multiple groups profileplot Profile plot grss Graph slide show graph2tex Convert Stata Graph to .eps file with LaTeX code ^Other Research and Misc Tools^ chi2power Compute power for contigency tables csgof Chi-square goodness of fit test do2htm Convert .do file to .htm file, with graphs included emeans Extended means command, including quadratic means extrans Examine effects of transformations gstudy Generalizability study program gtab Tables using Stata graph window (courtesy Adrian Mander) hilo Display highest and lowest values of variable hplot2 Horizontal plot using ascii characters largest Program to display largest "n" observations pred_eq Creates and tests imputation models (equations) for ice mctest Multiple choice test item analysis ml2mixed Convert from multilevel models to mixed models refgroup Set reference group for coded variables robmean Robust estimates of central tendency rtab Reverse tabulate, yielding percentiles showmarkers Show graph markers varying marker options spagplot Spaghetti Plots smallest Show smallest values stata2mlwin Convert Stata data files to MLwiN files stata2mplus Convert Stata data files to Mplus files stfit Fit statistics for survival models sumsum Compute sums of variables, and sums across variables tablabel Tabulate values for each value label including zero counts tablist Makes tables and crosstabs using list style output tabmiss Make tables of number of missing and non-missing values vartable Show table of means and variances wincorr Winsorized "robust" correlation milrtest Performs a likelihood ratio test on nested models for multiply imputed datasets after -mim-. ----------------------------------------------------------------------------------------------------------------------------------------
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Bruce Weaver
Email: [email protected]
Version: Stata/MP 19.5 (Windows)
Crypticity belongs in crosswords, not code! 🤨Comment
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Thank you very much Clyde Schechter and Bruce Weaver. Why I ask that question? Because both the first poster and her replier referred to the -omega- command in SSC. SEE #5 and #14:
I had a closer look at -omega- from SSC and found that -omega- calculates omega using standardized items, whereas you compared this measure of reliability to alpha using unstandardized items.So if it once was in SSC, why it be deleted? There's some bug in the command that its author withdrew himself? Or any other reasons? For the people who once installed -omega- from SSC, should they retain and use this command that no longer exists?When using -omega- (from SSC) you should take care that all items correlate positively with the total score of the remaining items (see the -omega- options "reverse" or "noreverse").Comment
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I believe omega might have been on ssc prior to a more recent command by the same author, Brian Shaw, was published in Stata Journal. The newer command is omegacoef. I have both installed and can confirm the are more or less identical.
Code:net sj 21-4 st0660
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