tutor
A PHP Error was encountered
Severity: Warning
Message: Undefined array key "userid"
Filename: views/question.php
Line Number: 212
Backtrace:
File: /home/statpmkj/public_html/application/views/question.php
Line: 212
Function: _error_handler
File: /home/statpmkj/public_html/application/controllers/Questions.php
Line: 416
Function: view
File: /home/statpmkj/public_html/index.php
Line: 315
Function: require_once
Determine whether the study depicts an observational study or an experiment.
Fifty patients with lung cancer are divided into two groups. One group receives an experimental drug to fight cancer comma the other a placebo. After two years, the spread of the cancer is measured.
Does the description correspond to an observational study or an experiment?
