Finally ... at the age of 50 (!) ... I was able to write my first PHP program.
Based on the results of logistic regression model (the intercept and the program impact estimate -- all expressed in logit), this program allows a user to calculate an odds ratio statistic and a standardized effect size (Cox index). The algorithm can be found in What Works Clearinghouse's standard document:
I replied on the following materials:
Udemy, Reece Kenny's Create a REAL Social Network like Facebook in PHP + MySQL. Honestly I didn't complete this course, but I learned how to run PHP and MySQL on my PC by installing XAMPP and running files from the XAMPP's subfolder (C:\xampp\htdocs). I also would have never figured out how to look at results by opening the file from localhost (e.g., http://localhost/calc.php).
Michiko's code. I first copied her simple calculator example and modified it to make my program.