\(\newcommand{\xb}{{\bf x}}

\newcommand{\betab}{\boldsymbol{\beta}}\)Before you use or distribute your estimation command, you should verify that it produces correct results and write a do-file that certifies that it does so. I discuss the processes of verifying and certifying an estimation command, and I present some techniques for writing a do-file that certifies **mypoisson5**, which I discussed in previous posts.

This is the twenty-fifth post in the series **Programming an estimation command in Stata**. I recommend that you start at the beginning. See Programming an estimation command in Stata: A map to posted entries for a map to all the posts in this series.

**Verification versus certification**

Verification is the process of establishing Read more…

This post was written jointly with Yulia Marchenko, Executive Director of Statistics, StataCorp.

As of update 03 Mar 2016, **bayesmh** provides a more convenient way of fitting distributions to the outcome variable. By design, **bayesmh** is a regression command, which models the mean of the outcome distribution as a function of predictors. There are cases when we do not have any predictors and want to model the outcome distribution directly. For example, we may want to fit a Poisson distribution or a binomial distribution to our outcome. This can now be done by specifying one of the four new distributions supported by **bayesmh** in the **likelihood()** option: **dexponential()**, **dbernoulli()**, **dbinomial()**, or **dpoisson()**. Previously, the suboption **noglmtransform** of **bayesmh**‘s option **likelihood()** was used to fit the exponential, binomial, and Poisson distributions to the outcome variable. This suboption continues to work but is now undocumented.

For examples, see *Beta-binomial model*, *Bayesian analysis of change-point problem*, and *Item response theory* under *Remarks and examples* in **[BAYES] bayesmh**.

We have also updated our earlier “Bayesian binary item response theory models using bayesmh” blog entry to use the new **dbernoulli()** specification when fitting 3PL, 4PL, and 5PL IRT models.

I make **predict** work after **mypoisson5** by writing an ado-command that computes the predictions and by having **mypoisson5** store the name of this new ado-command in **e(predict)**. The ado-command that computes predictions using the parameter estimates computed by ado-command **mytest** should be named **mytest_p**, by convention. In the next section, I discuss **mypoisson5_p**, which computes predictions after **mypoisson5**. In section Storing the name of the prediction command in e(predict), I show that storing the name **mypoisson5_p** in **e(predict)** requires only a one-line change to **mypoisson4.ado**, which I discussed in Programming an estimation command in Stata: Adding analytical derivatives to a poisson command using Mata.

This is the twenty-fourth post in the Read more…

**Overview**

I describe how to generate random numbers and discuss some features added in Stata 14. In particular, Stata 14 includes a new default random-number generator (RNG) called the Mersenne Twister (Matsumoto and Nishimura 1998), a new function that generates random integers, the ability to generate random numbers from an interval, and several new functions that generate random variates from nonuniform distributions.

**Random numbers from the uniform distribution**

In the example below, we use **runiform()** to create Read more…

\(\newcommand{\xb}{{\bf x}}

\newcommand{\betab}{\boldsymbol{\beta}}\)Using analytically computed derivatives can greatly reduce the time required to solve a nonlinear estimation problem. I show how to use analytically computed derivatives with **optimize()**, and I discuss **mypoisson4.ado**, which uses these analytically computed derivatives. Only a few lines of **mypoisson4.ado** differ from the code for **mypoisson3.ado**, which I discussed in Programming an estimation command in Stata: Allowing for robust or cluster–robust standard errors in a poisson command using Mata.

This is the twenty-third post in the series **Programming an estimation command in Stata**. I recommend that you start at the beginning. See Programming an estimation command in Stata: A map to posted entries for a map to all the posts in this series.

**Analytically computed derivatives for Poisson**

The contribution of the *i*(th) observation to the log-likelihood function for the Poisson maximum-likelihood estimator is Read more…