Two nationwide studies examine endoscopist performance and colorectal cancer after colonoscopy. Surveillance screening colonoscopy is based on characteristics of removed adenomas but not the endoscopists. In this issue Gastroenterology, Wieszczy et al examined endoscopists (CRC) risk in a Polish cohort. A total 173,288 colonoscopies were performed between 2000 2011 followed up until 2017. Of 26...

Binary covering arrays of strength t are 0–1 matrices having the property that for each t columns and each of the possible 2 sequences of t 0’s and 1’s, there exists a row having that sequence in that set of t columns. Covering arrays are an important tool in certain applications, for example, in software testing. In these applications, the number of columns of the matrix is dictated by the app...

In a recent paper by this author, constructions of linear binary covering codes are considered. In this work, constructions and techniques of the earlier paper are developed and modified for q-ary linear nonbinary covering codes, q 2 3, and new constructions are proposed. The described constructions design an infinite family of codes with covering radius R based on a starting code of the same c...

The minimum number of rows in covering arrays (equivalently, surjective codes) and radius-covering arrays (equivalently, surjective codes with a radius) has been determined precisely only in special cases. In this paper, explicit constructions for numerous best known covering arrays (upper bounds) are found by a combination of combinatorial and computational methods. For radius-covering arrays,...

A covering array CA(N ; t, k, v) is an N × k array such that every N × t sub-array contains all t-tuples from v symbols at least once, where t is the strength of the array. Covering arrays are used to generate software test suites to cover all t-sets of component interactions. The particular case when t = 2 (pairwise coverage) has been extensively studied, both to develop combinatorial construc...

Covering models have found many applications in a wide variety of real-world problems; nevertheless, some assumptions of covering models are not realistic enough. Accordingly, a general approach would not be able to answer the needs of encountering varied aspects of real-world considerations. Assumptions like the unavailability of servers, uncertainty, and evaluating more factors at the same ti...