### Archive

Posts Tagged ‘power’

## Just released from Stata Press: An Introduction to Stata for Health Researchers, Fifth Edition

Stata Press is pleased to announce the release of An Introduction to Stata for Health Researchers, Fifth Edition, by Svend Juul and Morten Frydenberg. This book debuted at #1 on Kindle’s new release list for Probability & Statistics and debuted on the top ten list on Kindle’s new release list for Mathematics. Read more…

## Calculating power using Monte Carlo simulations, part 5: Structural equation models

In our last four posts in this series, we showed you how to calculate power for a t test using Monte Carlo simulations, how to integrate your simulations into Stata’s power command, and how to do this for linear and logistic regression models and multilevel models. In today’s post, I’m going to show you how to estimate power for structural equation models (SEM) using simulations.

Our goal is to write a program that will calculate power for a given SEM at different sample sizes. We’ll follow the same general procedure as the previous two posts, but the way we’ll go about simulating data is a bit different. Rather than individually simulating each variable for our specified model, we’ll be simulating all our variables simultaneously from a given covariance matrix. Means for each of the variables can also be used to simulate the data if your SEM has a mean structure, such as in group analysis or growth curve analysis. Read more…

Categories: Statistics Tags:

## Calculating power using Monte Carlo simulations, part 4: Multilevel/longitudinal models

In my last three posts, I showed you how to calculate power for a t test using Monte Carlo simulations, how to integrate your simulations into Stata’s power command, and how to do this for linear and logistic regression models. In today’s post, I’m going to show you how to estimate power for multilevel/longitudinal models using simulations. You may want to review my earlier post titled “How to simulate multilevel/longitudinal data” before you read this post. Read more…

Categories: Statistics Tags:

## Calculating power using Monte Carlo simulations, part 3: Linear and logistic regression

In my last two posts, I showed you how to calculate power for a t test using Monte Carlo simulations and how to integrate your simulations into Stata’s power command. In today’s post, I’m going to show you how to do these tasks for linear and logistic regression models. The strategy and overall structure of the programs for linear and logistic regression are similar to the t test examples. The parts that will change are the simulation of the data and the models used to test the null hypothesis. Read more…

Categories: Statistics Tags:

## Calculating power using Monte Carlo simulations, part 2: Running your simulation using power

In my last post, I showed you how to calculate power for a t test using Monte Carlo simulations. In this post, I will show you how to integrate your simulations into Stata’s power command so that you can easily create custom tables and graphs for a range of parameter values. Read more…

Categories: Statistics Tags:

## Calculating power using Monte Carlo simulations, part 1: The basics

Power and sample-size calculations are an important part of planning a scientific study. You can use Stata’s power commands to calculate power and sample-size requirements for dozens of commonly used statistical tests. But there are no simple formulas for more complex models such as multilevel/longitudinal models and structural equation models (SEMs). Monte Carlo simulations are one way to calculate power and sample-size requirements for complex models, and Stata provides all the tools you need to do this. You can even integrate your simulations into Stata’s power commands so that you can easily create custom tables and graphs for a range of parameter values. Read more…

Categories: Statistics Tags:

## Stata 13 ships June 24

There’s a new release of Stata. You can order it now, it starts shipping on June 24, and you can find out about it at www.stata.com/stata13/.

Well, we sure haven’t made that sound exciting when, in fact, Stata 13 is a big — we mean really BIG — release, and we really do want to tell you about it.

Rather than summarizing, however, we’ll send you to the website, which in addition to the standard marketing materials, has technical sheets, demonstrations, and even videos of the new features.

And all 11,000 pages of the manuals are now online.