Table of Contents
Conduct Monte Carlo based power analysis using the path diagram interface
Once can conduct power analysis using Monte Carlo based method by drawing a path diagram with population parameters. An example is given in the figure below:
Rules to draw the path diagram
Shapes
: Observed variables.
: Latent variables / factors
: Mean / intercept
: Skewness/kurtosis
: Missing data
: One-headed arrows for regression paths/factor loadings
: Double-headed arrows for variances / covariances
Rules
- Click or or to draw the shape directly.
- To draw, first select one of the above three shapes and then click the button on the left panel.
- To draw, first select or , and then click button on the left panel.
- To draw paths between two shapes
- Method 1: Click or , then drag your mouse from the start variable to the end variable while pressing the left button of your mouse.
- Method 2: Click the start variable, then click the arrow path, and then the end variable.
- Adjust the diagram. Click any shape to highlight it, then move it around.
- Copy the diagram. First select the shapes by clicking the shapes while holding the “Ctrl” key on your keyboard. Then, click the
button to paste. - While holing the “Ctrl” key, one can drag a selection window by pressing the right button of the mouse to select multiple shapes.
Rules to specify the population parameters
- A number such as 1, 0.5, and -2, on the path will be used as population parameters to generate data from the model and the path will be estimated as free parameters in Monte Carlo simulation.
- To fix a path in the estimation, use @. For example, @1 will be fixed at 1.
- A path can be provided a name.
- For example, a?0.5 means the parameter values is 0.5, the parameter name is a, and the path needs to be estimated.
- a@0.5 means the parameter values is 0.5, the parameter name is a, and the path will be fixed at 0.5 when estimating the model.
- To specify the skewness and kurtosis for an observed variables, using the path from to . Two numbers separated by “;” are used with first one denoting the skewness and the second one denoting the kurtosis.
- Default parameters
- By default, the unspecified variances will be given the value 1 and the unspecified covariance will be given the value 0.
- The unspecified regression/loading paths will be given a value 0.
- The unspecified mean/intercept will be givens a value 0.
Conduct the power analysis
Required input
- Sample size: an integer number for sample size
- Significance level: 0.05 typically
- MC replications: How many Monte Carlo replications are used to estimate power. 1000 typically.
- Power parameters: Parameters other than specified in the diagram. For example, one can get the power for an indirect effect a*b. To get it, specify ab := a*b. Notice that “:=” is used to define a new parameter. Each line provides one such parameter.
- Notes: put a note for the analysis.
Required input
- To save the current path diagram, click the button
- To open an older path diagram, click the button
- To run the power analysis, click the button
- To see the output of the power analysis, click the button
- To download the path diagram as a SVG figure, click the button
- To draw a new path diagram, click the button
