Wells, Memon, & Penrod, 2006), suggesting that memory for the perpetrator is expressed more efficiently in the sequential lineup. Past research had suggested that the sequential lineup is superior to the simultaneous lineup because it leads to a reduced number of incorrect identifications without affecting the number of correct identifications (e.g. In contrast to the more traditional simultaneous lineup, in which all items are presented to the eyewitness at the same time, items in the sequential lineup are presented one at a time. The sequential lineup has been proposed as one such procedure (Lindsay & Wells, 1985). We also provide supplemental materials for fitting a signal detection model to simultaneous lineup data.Ī major goal of eyewitness research is to develop procedures that maximize correct identifications and minimize incorrect identifications by eyewitnesses. We show that the reason our results differ from some that have been published previously is due to the way in which eyewitness performance is measured in those studies where they are susceptible to distortion by structural features of the procedures. Our results revealed little to no simultaneous advantage in underlying discriminability, although the effect may be smaller than our study could detect, and a substantial shift in response bias in that eyewitnesses given sequential lineups require more evidence to identify an item. We developed a set of formal models based on signal detection theory and applied them to comparative data drawn from historic and contemporary studies in order to compare underlying memory performance between simultaneous and sequential lineups. In addition, to the degree that this supports theories such as DFDT, these can be used to develop improved lineup procedures that maximize performance. If the sequential lineup is inferior, this has important implications for procedural fairness in those jurisdictions that currently rely on it. This is consistent with diagnostic feature detection theory (DFDT), which attributes this difference to the greater ability of witnesses presented with a simultaneous lineup to compare different items and to isolate features that are uniquely shared by the perpetrator and the target item. Contrary to prior consensus, recent research employing signal detection measures has reported that simultaneous lineups may be superior to sequential lineups. Sequential lineups are currently used by police jurisdictions in the USA, Canada and the United Kingdom. We discuss the implications of these results for the diagnostic feature detection theory and other kinds of sequential lineups used in current jurisdictions. We found that although responses tended to be more conservative for sequential lineups there was little or no difference in underlying discriminability between the two procedures. We fit the models to the corpus of studies originally described by Palmer and Brewer (2012, Law and Human Behavior, 36(3), 247–255), to data from a new experiment and to eight recent studies comparing simultaneous and sequential lineups. In this study we developed models of simultaneous and sequential lineup presentations and used these to compare these procedures in terms of underlying discriminability and response bias, thereby testing a key prediction of diagnostic feature detection theory, that underlying discriminability should be greater for simultaneous than for stopping-rule sequential lineups. We argue that resolution of this debate requires the development and application of appropriate measurement models. Debate regarding the best way to test and measure eyewitness memory has dominated the eyewitness literature for more than 30 years.