Recognizing Structural Non-Identifiability: When Experiments Don’t Provide Information about 1 Important Parameters and Misleading Models Can Still Have Great Fit 2 Philip J. Schmidt 1,* , Monica B. Emelko 1 , Mary E. Thompson 2 3 1 Department of Civil & Environmental Engineering, University of Waterloo, 200 University Ave. W, 4 Waterloo, Ontario N2L 3G1, Canada 5 2 Department of Statistics & Actuarial Science, University of Waterloo, 200 University Ave. W, Waterloo, 6 Ontario N2L 3G1, Canada 7 * Address correspondence to Philip Schmidt, University of Waterloo, 200 University Ave. W, Waterloo, 8 Ontario N2L 3G1, Canada; tel. +1(519)8884567 x36745; pj2schmidt@uwaterloo.ca 9 This is the peer reviewed version of the following article: “Recognizing Structural Nonidentifiability: When Experiments Do Not Provide Information About Important Parameters and Misleading Models Can Still Have Great Fit”, which has been published in final form at https://doi.org/10.1111/risa.13386. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited. Supplementary Content is freely available at https://doi.org/10.1111/risa.13386