What\u27s a Testlet and Why Do We Need Them?

In 1987, Wainer and Kiely proposed a name for a packet of test items that are administered together; they called such an aggregation a testlet. Testlets had been in existence for a long time prior to 1987, albeit without this euphonious appellation. They had typically been used to boost testing efficiency in situations that examined an individual\u27s ability to understand some sort of stimulus, for example, a reading passage, an information graph, a musical passage, or a table of numbers. In such situations, a substantial amount of examinee time is spent in processing the stimulus, and it was found to be wasteful of that effort to ask just one question about it. Consequently, large stimuli were typically paired with a set of questions. Experience helped to guide the number of questions that were used to form the testlet. It is easy to understand that if, for example, we were to ask some questions about a 250-word reading passage, we would find that as we wrote questions, it would get increasingly difficult to ask about something new. Thus, we would find that eventually the law of diminishing returns would set in and a new question would not be generating enough independent information about the examinee\u27s ability to justify asking it. In more technical language, we might say that the within-testlet dependence among items limits the information that is available from that 250-word passage

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements