The Tenth Circuit recently affirmed the United States District Court of New Mexico’s decision striking a plaintiff’s expert’s testimony for failure to test his theory. See Heer v. Costco Wholesale Corp., No. 14-2009, 2014 WL 5462336 (10th Cir., Oct. 29, 2014). In a products liability action involving an allegedly defective metal step stool, the expert witness conducted an examination, which consisted of measuring the step stool and visually observing the step stool. Based on this limited examination, the expert concluded that the injuries were caused by product misuse and opined that a different product design would not have caused the injury. The district court concluded that the expert's opinion was unreliable because he did not test his hypothesis or test any alternative designs that he propose. Additionally, the court concluded that his testimony was not scientific because he simply relied on visual inspections and measurements of the stool and deposition testimony. He conducted no testing nor did he compare the product to any safety standards. Accordingly, the opinions were conclusory and unsubstantiated.