Funding for this research was provided by:
Division of Social and Economic Sciences (1521855, 1521855)
Division of Social and Economic Sciences (1521855)
Division of Mathematical Sciences (1621853, 1621853)
Article History
Received: 19 April 2018
Accepted: 11 July 2019
First Online: 13 August 2019
Change Date: 13 September 2019
Change Type: Correction
Change Details: The original version of this article unfortunately contained a mistake in its pdf version. Due to a formatting problem, the ‘tilde’ which is supposed to stay on top of ‘x’ or ‘y’ is in the middle, overlapping the variables. The online version of this article does not have this problem.
Compliance with ethical standards
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: The opinions expressed herein are those of the authors alone and do not reflect the opinion of the NSF.