Simultaneous v. Sequential Lineups: What Do We Really Know?

Ebbe B. Ebbesen and Heather D. Flowe

University of California, San Diego[1]

Abstract

Both conceptual and meta-analyses of the effects of simultaneous and sequential lineup testing procedures on false alarm and hit rates suggest that recent interest in moving to sequential lineups might be premature. A simple criterion-shift model based on signal detection theory accounted for the results from the meta-analysis raising concern that the previously accepted relative vs. absolute decision strategy view and the claim that hit rates will be unaffected by a change in procedure may both be incorrect. Monte-Carlo simulation results raise the possibility that serial position might play a much larger and more complicated role in performance on sequential lineups than has been considered. Considerably more research is needed before the sequential procedure is adopted.

INTRODUCTION

Recently, the National Institute of Justice collected a group of detectives, prosecutors, defense attorneys, and psychologists together to write guidelines for various agencies in the criminal justice system. The effort resulted in a report (Eyewitness evidence: A guide for law enforcement, 1999) that provided procedures for improving the collection and documentation of eyewitness testimony and identification, especially recommendations for conducting lineups. In particular, the guidelines suggest that sequential lineups produce more reliable identifications than simultaneous lineups. In simultaneous lineups, investigators present all of the potential choices together in time. In sequential lineups, the choices are presented one at a time in sequence. Studies comparing the two procedures have generally concluded that the rate of false alarms is lower for sequential than simultaneous lineups while the rate of hits is no different. Although the guidelines stop short of explicitly recommending one lineup procedure over another (due to a lack of consensus on the issue), police agencies could change their practice based on the guideline’s assertion that sequential lineups produce higher accuracy rates. For example, New Jersey, the first state in the US to incorporate the guidelines into police officer training, urges its officers to conduct sequential lineups when possible (http://www.state.nj.us/lps/dcj/agguide/photoid.pdf).

Adopting one lineup procedure over another obviously could have a significant impact on criminal case outcomes (Levi, 1998). As such, it is important to evaluate the decision strategy models and empirical evidence that have been advanced to account for the differential accuracy rates observed between the two lineup procedures. The assumed advantage of the sequential procedure is based on three things: 1) models of the purportedly different decision strategies that arise from the two test procedures (Lindsay & Wells, 1985), 2) evidence from laboratory research that seems consistent with the proposed model of how witnesses choose from simultaneous lineups (Lindsay, Lea, Nosworthy, & Fulford, 1991; Wells, 1993; Wells et al., 1998), and 3) laboratory research comparing accuracy rates across the two lineup procedures (Cutler & Penrod, 1988; Levi, 1998; Lindsay, Lea, & Fulford, 1991; Lindsay, Lea, Nosworthy et al., 1991; Lindsay & Wells, 1985; Lindsay, 1999; Lindsay, Pozzulo, Craig, & Lee, 1997; Parker & Ryan, 1993; Sporer, 1994).

In this article, we review the empirical evidence and conceptually analyze the decision models that have been developed to account for the differential accuracy rates observed in simultaneous and sequential lineup studies. Signal detection theory and Monte-Carlo simulations of eyewitness decision-making in the two lineup procedures aid our analysis. We also present a meta-analysis of the accuracy rates obtained in the past 25 years of published lineup identification research. Overall, the analyses suggest that an alternative view, a criterion-shift model based on signal detection theory, better accounts for apparent differences in identification accuracy across the two procedures. This account raises as yet unresolved issues that require considerably more research before we fully understand eyewitness performance in lineups. We conclude that it seems premature to recommend the universal adoption of the sequential over the simultaneous lineup procedure at this time.

Research and theory on relative decision model

A widely accepted explanation for the differences between simultaneous and sequential lineups is that eyewitnesses use a relative decision strategy when examining a simultaneous lineup and an absolute decision strategy when looking at a sequentially presented one (Lindsay, Lea, Nosworthy et al., 1991; Lindsay & Wells, 1985; Lindsay, 1999; Lindsay et al., 1997; Sporer, 1994; Wells et al., 1998).[2] The logic is that when multiple faces are presented simultaneously, witnesses will compare all of the choices to each other looking for the most familiar person in the display. When the most familiar face is selected, they will choose that person as the culprit. In contrast, when faces are presented one at a time sequentially, an absolute "identity" judgment is made because the opportunity to compare across the alternatives is considerably reduced. Witnesses are presumably forced to base their decision on how well each person’s appearance matches (or is inconsistent with) information stored in memory about the culprit. Consequently, the most familiar person will be chosen only if that person sufficiently matches the contents of memory.[3] If no one matches memory to a sufficient extent, the witness rejects the entire lineup.

Laboratory studies suggest that the use of the sequential procedure can lower the rate at which innocent suspects are chosen from culprit absent lineups. Additionally, these studies seem to find that the rate at which the actual culprit is chosen when present in the lineup does not differ between simultaneous and sequential lineups. As described, this outcome protects the innocent without reducing the odds that the guilty will go free—clearly a desirable outcome.

Empirical Evidence for Relative Judgment in Simultaneous Lineups

Some might argue that sufficient experimental evidence already exists to support the claim that eyewitnesses use a relative judgment strategy in simultaneous lineups and an absolute one in sequential lineups. In fact, New Jersey Attorney General John Farmer, in his guidelines calling for the use of sequential lineups, reported that scientific studies have “proven that witnesses have a tendency to compare one member of a lineup to another, making relative judgments about which individual looks most like the perpetrator” (http://www.state.nj.us/lps/dcj/agguide/photoid.pdf). Despite the Attorney General’s claim, the main concern of research examining different lineup procedures has been whether the two lineup procedures produce different accuracy rates and not the precise nature of the differences in decision strategy in the two procedures. Moreover, no experiment to date has been designed to test the idea that eyewitnesses use an absolute judgment strategy when confronted with a sequential lineup. In this section, research findings that are usually cited as evidence for relative judgment in simultaneous lineups (Wells et al., 1998) are reviewed. These include research involving the removal without replacement procedure, lineup admonishment, self-report data on judgment strategy, the dual lineup procedure, and lineup member to perpetrator similarity. Throughout, we argue that the research, hardly any of which was originally designed to test the parameters of the relative judgment model, is far from conclusive, in part because it fails to eliminate the alternative explanation that witnesses employ absolute comparisons in both simultaneous and sequential lineups.

Throughout this paper, we assume that identification (or recognition) is inherently a comparison task. That is, unless witnesses are just guessing, they would be expected to compare the items presented to them with some representation of information that they have in memory, even if that information is familiarity-based. The details of what is compared and exactly how the comparison is accomplished need not be made specific to understand that such comparisons might result in a wide range of values. Some items would yield very good matches and some very poor matches depending on what is in memory and the nature of the items that are presented to the witnesses. If this view is correct, witnesses would have to decide whether the degree of match was sufficient to claim identity. That is, a witness would have to set a criterion for deciding whether presented faces were sufficiently identical to the contents of his or her memory of the culprit before claiming that the face and the memory are the same. We argue that the possibility that witnesses might set “absolute” degree-of-match criteria in both sequential and simultaneous lineups forms the basis for an alternative explanation of findings that have been taken as support for the relative decision model.

Removal without replacement.

The “removal without replacement” procedure (Wells, 1993) has been cited as the best evidence that eyewitnesses use a relative judgment strategy when confronted with a simultaneous lineup (Wells et al., 1998). The removal without replacement procedure involves two parts. After viewing a staged crime in the laboratory, eyewitnesses are shown a culprit-present simultaneous lineup. Both the distribution of choices over all available alternatives in the lineup and the no choice rate for this group are recorded. In the second part, another group of eyewitnesses undergoes similar experimental procedures, except that the target’s picture has been removed from the lineup and not replaced with any other photograph. According to Wells (1993), if a relative judgment strategy is being used, the eyewitnesses viewing the target-removed lineup will be inclined to select the most familiar face from the remaining set of foils instead of correctly rejecting the lineup. This prediction assumes that the choices of the target in the target present lineup were based on the fact that the target was the most familiar of all of the presented alternatives. On the other hand, if witnesses were using an absolute judgment strategy in such lineups, then when viewing the target-removed lineup, they should correctly reject the lineup because the culprit is not there. As shown in Figure 1, Wells (1993) found that the subjects were more likely to pick a foil and less likely to reject the lineup after the target had been removed.

Figure 1. Foil and target choice rates from Wells (1993) study of the effects of removing and not replacing a target in simultaneous lineups.

The relative decision strategy model assumes that witnesses examine all of the choices in a simultaneous lineup and then choose the most familiar alternative. Were this the strategy, witnesses would always choose someone from simultaneous lineups because, except in the rare case of a tie, one alternative should always be the most familiar (regardless of how unfamiliar that alternative might be). Not only is the correct rejection rate for both groups in the Wells study higher than one might expect if all subjects were using a relative decision strategy, we know that witnesses frequently fail to choose someone from simultaneous lineups (even when the culprit is present) both in the real world (Behrman & Davey, 1999; Tollerstrup, Turtle, & Yuille, 1994) and in laboratory simulation studies (Lindsay, Lea, & Fulford, 1991; Lindsay & Wells, 1985; Lindsay et al., 1997; Pozzulo & Lindsay, 1999; Sporer, 1994; Yarmey & Morris, 1998). For example, in our meta-analysis (reported later in this paper), adult witnesses tested in 114 experiments with simultaneous target present lineups failed to pick anyone an average of 51.7% of the time. In 84 experiments employing target absent simultaneous lineups, the average correct rejection rate was 49.9%. In addition, about a third of the witnesses who viewed the target-removed lineup in the Wells (1993) study refused to pick the most familiar person when they rejected the entire lineup. In short, a refinement of the relative decision-strategy idea that witnesses always pick the most familiar person is therefore necessary to explain the fact that about half (taking all of the studies together) of all adult witnesses in published experiments fail to choose the most familiar alternative when the target is absent.

One possibility originally proposed by Lindsay & Wells (1985) and recently discussed by Gonzalez, Ellsworth, & Pembroke (1993) in the context of comparing single-suspect "showup" procedures to simultaneous lineups is the view that witnesses employ a combination of a relative and an absolute strategy in a simultaneous lineup.[4] Namely, they might look at all of the choices, pick the most familiar, and then compare this most familiar-looking person to the same kind of absolute similarity standard that is assumed to be used in showups and in sequential lineups.[5] That is, they might decide whether the most familiar person’s looks matched those of the recalled culprit to a sufficient degree. If the match exceeds the absolute standard, then the witness would select that person as the culprit.

Once one allows for the possibility that witnesses confronted with a simultaneous lineup might do more than always select the most familiar option, it is possible to refine the relative decision model proposed to explain Wells’ (1993) findings. In particular, it seems reasonable that more than one face will exceed the absolute criterion set by witnesses for some witness-lineup combinations. If so, witnesses would have to choose among the subset of presented faces that were familiar enough to exceed their criteria. Presumably, they would choose the face that exceeded the standard the most. If witnesses used this strategy in simultaneous lineups, they would be expected to behave as they did in Wells’ (1993) removal without replacement study. After all, removing the target would mean that the one face most likely to exceed the standard was no longer available. However, one or more of the remaining faces, although less familiar than the target, might still be above the criterion set by witnesses. As a result, when presented with the remaining foils, some proportion of the witnesses would be expected to select one of them. How many witnesses would select one of the remaining foils would depend on the rate, over witnesses, at which one or more of the remaining foils exceeded whatever standard the witnesses set. Lower standards and greater perceived similarity between memory of the culprit and each of the foils would mean more witnesses from the second group would choose one of the remaining foils.

If one accepts the notion that witnesses might employ a criterion in simultaneous lineups, then what is different between simultaneous and sequential lineups? Faces are selected in both cases only if they exceed some absolute standard or “match criterion”. One possible answer is that witnesses employ an absolute standard in both lineup procedures but they set the standard lower in simultaneous than sequential lineups. A lower standard in simultaneous lineups could explain why witnesses make more false alarms in target absent simultaneous than sequential lineups. On the other hand, this differential criterion view also predicts that witnesses should make more correct choices in simultaneous compared to the sequential procedure when the target is present. That is, a lower criterion would increase the rate at which witnesses chose both innocent "look-alikes" in blank lineups and the actual culprits in target present lineups because faces that were less than perfectly matched to memory representations would be more likely to exceed the lower criterion. Another way of stating this prediction is that witnesses should be more likely to make a choice with lower than higher decision standards. These predictions seem inconsistent with conclusions from individual studies that typically report that the simultaneous/sequential difference is in false alarm rates, but not in hit rates (Lindsay & Wells, 1985; Sporer, 1993). As a result, at first look, the idea that differentially strict absolute criteria are used in both types of lineups seems inconsistent with current findings.[6] We will return to this issue in subsequent sections in which we provide a signal detection analysis of lineup decisions and the results from a meta-analysis of the lineup literature.

Effect of admonishment.

A second source of evidence that relative judgments are made in simultaneous lineups is the effect that biased lineup instructions have on identification decisions (Wells et al., 1998). Eyewitnesses who are admonished that the culprit “may or may not be present” prior to viewing a target absent lineup are less apt to make false identifications than eyewitnesses who are not given such a suggestion. In a recent meta-analysis, Steblay (1997) found admonishing witnesses that the culprit might not be in the lineup increases the rate at which target absent lineups are rejected while having “minimal” effect on the rate at which the culprit is correctly identified. That is, admonishment to use a stricter criterion only seems to affect errors made to target absent lineups. One interpretation of this outcome is that admonishment discourages eyewitnesses from making relative judgments (Wells, et al. 1998). Presumably, if witnesses are led to believe that the culprit is in the lineup, they compare lineup choices and select the most familiar alternative. Witnesses who do not possess such a belief avoid making familiarity judgments and instead compare each lineup member to their actual memories of the culprit.

Though this is a plausible account, multiple alternative hypotheses could explain why admonishment affects false alarm rates in simultaneous lineups other than the fact that witnesses use a relative decision strategy. For example, witnesses who are admonished might false alarm less often because admonishment forces them to think more carefully about the culprit’s features. That is, admonished witnesses might extract or analyze information from faces differently than those who are not admonished. As a result, they could extract information that is more diagnostic of the culprit’s actual appearance. Alternatively, and more reasonably, admonishment might affect how witnesses respond to a match between what is in memory and the perceived characteristics of the face. In particular, admonished witnesses might require a more perfect match before they say one of the faces is the culprit. Believing more strongly that the culprit is in the lineup, witnesses who were not admonished might select foils that only matched the contents of their memories to a slight degree. They simply set a lower criterion that allows them to conclude that less well-matched foils are close enough in appearance to their memory of the perpetrator’s looks. Still a different possibility is that admonished witnesses might be more likely to look for features that are inconsistent with their recollections of the culprit’s looks. Regardless, the claim that admonishment influences people’s willingness to make relative judgments requires more critical testing to determine where and how admonishment exerts its effect in the decision process. Furthermore, exactly how admonishment would discourage relative judgment is not clear because the precise mechanisms involved in the relative judgment idea have received little theoretical treatment.

Self-reports of decision process.

In addition to the experimental research, self-report data has been used to investigate lineup judgment strategies (Lindsay, Lea, Nosworthy et al., 1991; Lindsay & Bellinger, 1999). Subjects tend to agree that they use a relative strategy when viewing a simultaneous lineup and an absolute strategy when viewing a sequential lineup. Furthermore, these studies find that people tend to be more accurate if they report using an absolute strategy rather than a relative one. Some subjects, however, have been known to report using an absolute strategy even though the experimenter observed them comparing the lineup pictures to one another (Lindsay, 1999). Equally important, self-reports of mental process might be driven by differences between the two procedures in a way that the actual decision processes are not. For example, subjects might be more likely to report that they compare pictures in a simultaneous lineup because they can shift their visual gaze from one picture to another but can not do so in a sequential lineup. Gaze shifting might have little to do with whether subjects are using an absolute similarity standard, however. Because people respond affirmatively in laboratory experiments that they used a given mental strategy does not preclude the possibility that they compared each picture to their memories and compared the result to a criterion regardless of method of presentation.

Dual lineup procedure.

Another research finding used to support the contention that relative judgment is used to select someone from simultaneous lineups is the effect that the dual lineup procedure has on accuracy rates. In the dual lineup procedure, eyewitnesses are first shown a blank lineup before they are presented with the actual lineup test. Wells (1984) found that participants who rejected the blank lineup, compared to those who picked someone out, were less likely to false alarm on a subsequently presented target absent lineup. Hit rates, however, did not differ depending on whether the participant chose someone from the blank lineup. Wells and his colleagues (1998) argued that blank lineups might be used to screen out witnesses who are prone to making relative judgments. More evidence is needed, however, to demonstrate that the witnesses who false alarmed were making relative comparisons. Other than the fact that they false alarmed, we have no other evidence to indicate that those witnesses used a relative judgment process.

More importantly, the dual lineup results are also consistent with a criterion-based account. Subjects who choose someone in the blank lineup might have lower criteria (e.g., accept less of a match between their recollections of the culprit’s looks and the appearance of the faces in the lineup) compared to other subjects. Thus, the dual lineup procedure might be screening out subjects who have lower criteria, not necessarily those who are inclined to make relative judgments. This competing explanation has not been empirically examined. Though not the central issue here, one also begins to wonder whether these results indicate that the tendency for relative judgment is a matter of individual differences in judgment, and not especially a problem inherent to simultaneous lineups.

Similarity

A final source of evidence taken as support for the relative judgment idea is an experimental outcome in which false alarm rates were influenced by the resemblance of the lineup members to the perpetrator (Wells, Rydell, & Seelau, 1993). In this experiment, the likelihood of participants selecting a foil from a lineup did not depend on whether only one person or all six persons in the lineup resembled the perpetrator. Presumably this is because with relative judgment someone will always be the most familiar alternative regardless of how similar the alternatives are to each other. In addition, the rate at which participants selected an innocent suspect from a target absent lineup was greater when he was the only one matching the description of the perpetrator. When only one alternative matched the perpetrator’s description, he should be the most familiar and therefore the most likely alternative to be chosen. Wells et al. (1998) argued that these findings support the use of a relative judgment strategy in simultaneous lineups.

Although these results do seem consistent with the relative decision model, a criterion model can explain the same pattern of outcomes. The fact that the innocent suspect was chosen more often when he was the only one matching the description of the perpetrator could be explained by the effect that the lineup similarity structure has on the odds that a given picture will exceed one’s criterion. If only one person resembles the culprit, he should be more likely to surpass the criterion than any other foil. Likewise, witnesses should be less likely to pick a given foil who looks like the culprit if he is surrounded by five other persons who also look like the culprit. By chance, one would expect the more foil pictures there are in a lineup resembling the culprit, the more some witnesses would find at least one of foils to be a better match to their memories of the perpetrator than the picture designated as the innocent suspect. As a consequence, they would be more likely to pick another similar looking foil instead of the innocent suspect.

Even if one rejects this criterion explanation for the pattern of results from the Wells, Rydell & Seelau (1993) study, the fact that a recent study by Tunnicliff & Clark (2000) did not replicate this pattern raises additional concerns. Tunnicliff & Clark (2000) found no effect on hit or false alarm rates of selecting foils on the basis of similarity to the suspect or on the basis of a match to the witness’s recalled description. As a result, we are left with the somewhat surprising possibility that the similarity effect reported by Wells, et al. (1993) will not replicate.

Despite some minor uncertainty, the results of empirical studies reviewed in this section seem to indicate that the rate of false alarms can be affected by a variety of experimental manipulations often with no change in hit rates. This pattern, a reduction in false alarms with little or no reduction in hit rates, has been interpreted as evidence for relative judgment processing in simultaneous lineups (Wells et al. 1998). This conclusion, however, would be justified only if an explicit and detailed model were available that described the structure and organization of the decision processes in a simultaneous lineup and other reasonable alternative models had been empirically eliminated. Unfortunately, the evidence for the use of a relative judgment process comes from a post-hoc evaluation of experiments that, in most cases, were not specifically designed to test whether a relative judgment strategy is used in simultaneous lineups. This kind of evaluation is a good place to start; but definitive policy concerning police lineup procedures ought to be based on more.

The relative judgment model reconsidered

Any model of how witnesses make choices from lineups will need to take account of two important empirical facts. The first is that participants in experiments reject simultaneous target absent lineups at a fairly high rate, and the second is the difference in identification performance produced by the simultaneous and sequential procedures.

The fact that witnesses frequently fail to pick anyone from simultaneous lineups suggests that they are doing more than simply picking the most familiar person from the lineup. As a result a process that allows participants to reject all members of a lineup must be an integral part of their decision strategies. Thus, a "two-process" model seems necessary to retain the idea that people use a relative decision process. However, such models can take several forms. For example, in a simultaneous lineup people might covertly select the most familiar face by comparing all familiarity values to each other. Once the most familiar face is selected, they could then compare it to an absolute decision criterion deciding whether it is familiar enough to choose. If the most familiar face exceeds the criterion, they select it. Otherwise they reject the entire lineup. Alternatively, people confronted with a simultaneous lineup could first compare each face to the same absolute criterion. If more than one face exceeds this standard, then the participants might apply a "relative" judgment or simple selection process and pick the one face that exceeds the standard by the greatest amount.[7] If no face exceeds the standard, they could reject the entire lineup. Thus, witnesses might employ a “relative” and then absolute or an absolute and then “relative” process. These different orders (and types) of strategies could produce different patterns of choice outcomes if the familiarity process tended to select a different face than the one that is most likely to be above the absolute criterion. Unfortunately, current conceptual analyses have not specified which (or whether both) of these possibilities is operating in simultaneous lineups.

One source of the lack of specificity in the relative decision strategy model has been whether "familiarity comparisons" might involve different processes and/or memory representations than those used when deciding whether a face exceeds an absolute “identity” decision criterion. For example, familiarity decisions might be based on different memory-evidence than that used to compare each choice with whatever identity information is in memory. Specific features might be more important in judging familiarity (Burton, Bruce, & Hancock, 1999; Hancock, Burton, & Bruce, 1996) but a more "holistic" process (Cottrell, Dailey, Padgett, & Adolphs, 2001; Farah, 1996; Farah, Wilson, Drain, & Tanaka, 1998) might be involved in judging identity (or vice versa). Alternatively, features that did not match the witness’s memory of the culprit might play a greater role in one procedure whereas features that matched the contents of memory might be more important in the other procedure. Were different facial representations, e.g., surface codes and eigenvalues verses relative location of key "premorph" features, (O'Toole, Wenger, & Townsend, 2001) used in familiarity judgments than in identity judgments, different specific faces might rise to the top when familiarity is the initial basis of selection than when identity is the initial basis. As a result, a final decision of the type, "Does this face look enough like the person I saw for me to pick him?" might be made to a different set of faces (across witnesses) if the faces were initially selected for familiarity than if they were selected for comparison to an identity-match criterion. While such reasoning might seem sensible, unless more detail is added (Roe, Busemeyer, & Townsend, 2001), these views cannot explain why false alarm rates and not hit rates seem to change with a change in testing procedure. After all, if familiarity-based choice processes were more likely to cause innocent look-alike examples to rise to the top when the culprit is absent, why would not the same processes cause the culprit to be more likely to rise to the top when he is present? Presumably the same familiarity-based reasons that caused an innocent look-alike to seem most familiar would also cause the culprit to seem most familiar.

Once one accepts the possibility that witnesses who are confronted with a simultaneous lineup might make decisions based on a “dual” strategy, it is only reasonable to wonder whether witnesses confronted with a sequential lineup might not use two strategies as well. For example, although the first face that witnesses see in a sequential lineup cannot be compared to faces that have yet to be seen, it is possible that the second face might be compared, in working memory, to a recalled image of the first face. Similarly, the third face might be compared to recalled images of both the second and the first, and so on. If the second face is less familiar than the first one, the witness might reject it. If it is more familiar, then the witness might compare it to an absolute standard in an attempt to determine identity. Thus, relative familiarity could affect whether later faces are rejected in sequential lineups. However, the comparisons would be between images of faces in working memory with the currently presented face in the sequence.

The effect of serial position on choice rates in sequential lineups

Another issue that is made more obvious by the previous discussion is the differential importance that serial position might play in sequential as opposed to simultaneous lineups despite some reports that the positioning of the target and his replacement have no effect on choice rates in sequential lineups (Lindsay & Wells, 1985; Sporer, 1993). Although it is likely that witnesses (in the U.S.A.) will initially scan photos in a simultaneous array from left to right in a manner consistent with reading habits, they are free to look back at any photo and move their attention around in a rather "free-form" manner. However, with sequentially presented lineups, the probability that a face with a particular absolute "degree of match" to memory for the culprit will be chosen should vary with its serial position in the lineup. In particular, whether a given face that exceeds a selection standard can even be chosen depends on whether another face that exceeds the same decision standard has already been presented in the sequence. If such a face has already been presented, then the witness will not have the opportunity to choose the target’s face. The later the target face appears in the sequence, the greater the number of opportunities that an earlier face will exceed the witness’s "match criterion" and the less the chances that the witness will even be able to pick the target.

We conducted a Monte-Carlo simulation of a six-person sequential lineup to examine more carefully than has been done previously the theoretical implications of the effect of position on the probability that a target face will be chosen in a sequential lineup. The simulation assumed that witnesses were allowed to pick only one face and that the procedure stopped either with the first pick or after all of the faces had been seen without a pick (Lindsay, Lea, & Fulford, 1991). Thus, review of previously rejected faces or multiple picks were not allowed. The simulation also assumed all pictures had a numerical value representing its recognition strength and that all five foils were selected from a unit normal distribution of “strengths” with mean zero and that the target was selected from another unit normal distribution wit