William Trochim https://www.socialresearchmethods.net/kb/intreval.php http://www.socialresearchmethods.net/kb/intreval.php http://www.socialresearchmethods.net/kb/intreval.php http://www.socialresearchmethods.net/kb/intreval.php http://www.socialresearchmethods.net/kb/intreval.php Introduction to Evaluation