# Binomial confidence intervals: exact vs. approximate

This graph and R code compares the exact vs. normal approximations for 95% binomial confidence intervals for n trials with either one success or 50% success.

# Bar plot with error bars in R

Here’s a simple way to make a bar plot with error bars three ways: standard deviation, standard error of the mean, and a 95% confidence interval. The key step is to precalculate the statistics for ggplot2.

# Calculate RMSE and MAE in R and SAS

Here is code to calculate RMSE and MAE in R and SAS. RMSE (root mean squared error), also called RMSD (root mean squared deviation), and MAE (mean absolute error) are both used to evaluate models. MAE gives equal weight to all errors, while RMSE gives extra weight to large errors.

# 100% stacked bar chart in SAS’s SGPLOT

A 100% stacked bar chart is useful for comparing the relative frequencies of an m x n table where frequencies in m are very different. While this is easy to do in Excel, SAS requires an extra step, which you could call a hack or a trick. First, let’s create an example data set. Say…

# Comparing continuous distributions with R

In R we’ll generate similar continuous distributions for two groups and give a brief overview of statistical tests and visualizations to compare the groups. Though the fake data are normally distributed, we use methods for various kinds of continuous distributions. I put this together while working with data from an odd distribution involving money where…

# Plotting individual growth charts

This R code draws individual growth plots as shown in “Applied Longitudinal Data Analysis: Modeling Change and Event Occurrence” by Judith D. Singer and John B. Willett, an excellent book on multilevel modeling and survival analysis. This code recreates figure 2.5 on page 32 with the caption, “OLS summaries of how individuals change over time.…

# Train neural network in R, predict in SAS

This R code fits an artificial neural network in R and generates Base SAS code, so new records can be scored entirely in Base SAS. This is intended to be a simple, elegant, fast solution. You don’t need SAS Enterprise Miner, IML, or any other special licenses, and R is free. You don’t need PMML.…

# Paired sample t-test in R

Let’s walk through using R and Student’s t-test to compare paired sample data. The book Statistics: The Exploration & Analysis of Data (6th edition, p505) presents the longitudinal study “Bone mass is recovered from lactation to postweaning in adolescent mothers with low calcium intakes”. The total-body bone mineral content (TBBMC) of young mothers was measured…