Category Archives: Computing and Others

Seasonal adjustment

What is seasonal adjustment?

Seasonal adjustment refers to a statistical technique that tries to quantify and remove the influences of predictable seasonal patterns to reveal nonseasonal changes in data that would otherwise be overshadowed by the seasonal differences. Seasonal adjustments provide a Continue reading Seasonal adjustment

Clustered Standard Errors in R

The easiest way to compute clustered standard errors in R is the modified summary(). I added an additional parameter, called cluster, to the conventional  summary() function. This parameter allows to specify a variable that defines the group / cluster in your data. The summary output will return clustered standard errors. Here is the syntax:

summary(lm.object, cluster=c("variable")) Continue reading Clustered Standard Errors in R

Example data – Clustered Standard Errors

The following R script creates an example dataset to illustrate the application of clustered standard errors. You can download the dataset here.

The script creates a dataset with a specific number of student test results. Individual students are identified via the variable student_id . The variable id_score comprises a student’s test score. In the test, students can score from 1 to 10 with 10 being the highest score possible. Continue reading Example data – Clustered Standard Errors

Robust Standard Errors in STATA

”Robust” standard errors is a technique to obtain unbiased standard errors of OLS coefficients under heteroscedasticity. In contrary to other statistical software, such as R for instance, it is rather simple to calculate robust standard errors in STATA. All you need to is add the option robust to you regression command. That is:

Continue reading Robust Standard Errors in STATA

Robust Standard Errors in R

One can calculate robust standard errors in R in various ways. However, one can easily reach its limit when calculating robust standard errors in R, especially when you are new in R. It always bordered me that you can calculate robust standard errors so easily in STATA, but you needed ten lines of code to compute robust standard errors in R. I decided to solve the problem myself and modified the summary() function in R so that it replicates the simple way of STATA. I added the parameter robust to the summary() function that calculates robust standard errors if one sets the parameter to true. With the new summary() function you can get robust standard errors in your usual summary() output. All you need to do is to set the robust parameter to true:

summary(lm.object, robust=T) Continue reading Robust Standard Errors in R

Robust Standard Errors in R – Function

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

Self-Hosted WordPress Permalink Problems – set AllowOverride all

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

Self-Hosted WordPress Permalink Problems – .htaccess permissions

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

Self-Hosted WordPress Permalink Problems – .htaccess exits

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