# semPower

semPower is an R-package that provides several functions to perform a-priori, post-hoc, and compromise power analyses for structural equation models (SEM).

Install `semPower` via CRAN or as follows:

``````install.packages("devtools")
library("devtools")
install_github("moshagen/semPower")``````

### Manual

``vignette("semPower")``

### Quick Examples

Determine the required sample size to detect misspecifications of a model (involving df = 100 degrees of freedom) corresponding to RMSEA = .05 with a power of 80% on an alpha error of .05:

``````ap <- semPower.aPriori(effect = .05, effect.measure = 'RMSEA', alpha = .05, power = .80, df = 100)
summary(ap)``````

Determine the achieved power with a sample size of N = 1000 to detect misspecifications of a model (involving df = 100 degrees of freedom) corresponding to RMSEA = .05 on an alpha error of .05:

``````ph <- semPower.postHoc(effect = .05, effect.measure = 'RMSEA', alpha = .05, N = 1000, df = 100)
summary(ph)``````

Determine the critical chi-square such that the associated alpha and beta errors are equal, assuming sample size of N = 1000, a model involving df = 100 degrees of freedom, and misspecifications corresponding to RMSEA = .05:

``````cp <- semPower.compromise(effect = .05, effect.measure = 'RMSEA', abratio = 1, N = 1000, df = 100)
summary(cp)``````

Plot power as function of the sample size to detect misspecifications corresponding to RMSEA = .05 (assuming df = 100) on alpha = .05:

``semPower.powerPlot.byN(effect = .05, effect.measure = 'RMSEA', alpha = .05, df = 100, power.min = .05, power.max = .99)``

Plot power as function of the magnitude of effect (measured through the RMSEA assuming df = 100) at N = 500 on alpha = .05:

``semPower.powerPlot.byEffect(effect.measure = 'RMSEA', alpha = .05, N = 500, df = 100, effect.min = .001, effect.max = .10)``

For more details and for a description how to express the magnitude of effect in terms of model parameters, see the manual.

### Citation

If you use `semPower` in publications, please cite the package as follows:

Moshagen, M., & Erdfelder, E. (2016). A new strategy for testing structural equation models.Structural Equation Modeling, 23, 54-60. doi: 10.1080/10705511.2014.950896