All posts by AV

Computing and Others, Econometrics

Robust Standard Errors in R – Function

9 Comments

One can calculate robust standard errors easily in STATA. However, one can easily reach its limit when calculating robust standard errors in R. Although there exist several possibilities to calculate heteroscedasticity consistent standard errors most of them are not easy to implement, especially for beginners. I modified the summary() function in R so that it replicates the simple way of STATA. You can find the new summary() function below. Furthermore, I uploaded the function to a github.com repository. This makes it easy to load the function into your R session. In order to see how you can import the new summary() function into your R session and how you can use it see this post here. Continue reading Robust Standard Errors in R – Function →

Econometrics

Violation of CLRM – Assumption 4.2: Consequences of Heteroscedasticity

3 Comments

Violating assumption 4.2, i.e. \sigma_{i}^{2} \neq \sigma_{j}^{2} \text{ for } i \neq j leads to heteroscedasticity. Recall, under heteroscedasticity the OLS estimator still delivers unbiased and consistent coefficient estimates, but the estimator will be biased for standard errors. Increasing the number of observations will not solve the problem in this case.

Fortunately, several ways exist to deal with heteroscedasticity: Continue reading Violation of CLRM – Assumption 4.2: Consequences of Heteroscedasticity →

Computing and Others

Self-Hosted WordPress Permalink Problems – set AllowOverride all

1 Comment

WordPress uses .htaccess to manipulate how Apache serves files from its root directory, and subdirectories thereof. Most notably, WP modifies this file to be able to handle pretty permalinks. However, Apache must allow the use of .htaccess files in order for WordPress to use the file. Set the parameter ”AllowOverwrite” of the file ”apache2.conf” file to ”All” in order to tell Apache to allow the use of .htaccess files. Continue reading Self-Hosted WordPress Permalink Problems – set AllowOverride all →

Computing and Others

Self-Hosted WordPress Permalink Problems – .htaccess permissions

2 Comments

In case you .htaccess exists and is placed in the right directory you should check if it has the right permissions and if the right user owns it. The right user should be your linux user handling WordPress. On Debian (it will be similar on other systems, I suppose) you can find the owner and the permission of a file or directory with the command  ls -l /path/to/directory. The output will tell you the permission on the file (”-rw-r–r–” in my case) and who owns the file (”www-data” in my example). The second ”www-data” indicates the group, which is identical than the owner in my case. Continue reading Self-Hosted WordPress Permalink Problems – .htaccess permissions →

Computing and Others

Self-Hosted WordPress Permalink Problems – .htaccess exits

3 Comments

The first thing one should check is if the file .htaccess exists in the root directory of the site (/var/www/html in my case). The root directory of your site should contain a file index.php, in the same folder there should be the file .htaccess. WordPress uses this file to manipulate how Apache serves files from its root directory, and subdirectories thereof. Most notably, WP modifies this file to be able to handle pretty permalinks. Continue reading Self-Hosted WordPress Permalink Problems – .htaccess exits →

Computing and Others

Self-Hosted WordPress Permalink Problems

2 Comments

Permalink problems can be a very annoying. The following post presents a guideline to fix the problem in a systematical way. Specifically, the post refers to the problem that pages, sites and posts of a self-hosted WordPress blog become inaccessible once one changes the permalink settings. Generally, there are various sources that can cause the same problem. Below you find a checklist that one can go through step by step to find the error. Continue reading Self-Hosted WordPress Permalink Problems →