The Serial Position Effect – Arizona Forensic Services, LLC

Snap Shot

The question: Does where an item falls in a sequence, whether a word in a list, a moment in an event, a photograph in a lineup, or a piece of evidence at trial, affect how well it is remembered or how much weight it receives?

What the research shows: In list learning, the first and last items are generally recalled better than the middle ones (primacy and recency), and the two advantages rest partly on different processes. In lineups, position can affect willingness to choose more than the ability to recognize, and in mock trials the order of openings and evidence can shift judgments in either direction.

What it does not show: The research has not established that witnesses generally remember the middle of a real event poorly, and it cannot show that a particular gap, detail, identification, or verdict was produced by position. Trial order effects are inconsistent in direction and depend on the task.

The law: Rule 702 and Houser govern expert testimony, and Arizona permits general memory testimony (Chapple, Nordstrom). Lineup position bears on suggestiveness under Mil. R. Evid. 321 and a Dessureault hearing; the order of evidence is controlled by the court under Rule 611(a).

Issues for each side: Prosecutors can explain uneven memory for a sequence as ordinary and should guard against position effects in lineups by randomizing and recording suspect position; defense counsel can examine where a suspect appeared and how a sequence was elicited, without treating position as proof that an identification or a memory is wrong.

Memory for a series of items is not even. In the classic laboratory task, the first few items and the last few are recalled better than those in the middle, so that recall plotted by position forms a bowed or U-shaped curve. The advantage for early items is the primacy effect; the advantage for late items is the recency effect. Together they make up the serial position effect, one of the oldest and most consistently replicated findings in memory research.

The effect reaches court in three ways. Witnessed events unfold in sequence, and lawyers sometimes ask whether gaps in the middle of an account are to be expected. Lineups, especially sequential lineups, present faces in order, and the position of the suspect may affect what a witness does. And trials themselves are sequences: opening statements, witnesses, exhibits, and closing arguments arrive in an order, and research on judgment has asked whether what comes first or last carries disproportionate weight.

This paper describes the classic findings and their explanations, what is known about serial position outside word lists, position effects in lineups, order effects in trial judgments, and the limits of that evidence. It then summarizes the federal, military, and Arizona law that the topic touches.

The Classic Finding

Murdock (1962) presented lists of unrelated words of varying lengths and asked participants to recall them in any order. Across list lengths, recall was highest for the last several items, high for the first few, and lowest and fairly flat across the middle. Glanzer and Cunitz (1966) then found that primacy and recency respond to different manipulations. When participants counted for about 30 seconds before recalling, the recency advantage disappeared while the primacy advantage remained. When items were presented more slowly, recall of early and middle items improved but recall of the final items did not. The authors took these dissociations as evidence that recency and primacy reflect different storage processes.

Serial position effects are not limited to unrelated words. Deese and Kaufman (1957) found position effects both with unorganized word lists and with verbal material that approximated connected text, although the shape of the curve depended on how the material was organized. That qualification matters for the courtroom: meaningful material, such as a story or an event, is remembered partly through its structure, and structure can change which parts are recalled best.

Why the Beginning and the End Are Favored

The traditional account draws on the distinction between a limited short-term store and a durable long-term store (Atkinson & Shiffrin, 1968). On this view, the first items in a list are rehearsed more often, because there is little else to rehearse when they arrive, and extra rehearsal transfers them to long-term memory. Rundus (1971) supported this by asking participants to rehearse aloud: early items were rehearsed more often than later ones, and recall tracked the number of rehearsals across the early part of the list. The last items, by contrast, are thought to be recalled well because they remain available in short-term or working memory when the test begins, which is why a brief filled delay eliminates recency but not primacy (Glanzer & Cunitz, 1966).

Later research showed that this two-store account is incomplete. Bjork and Whitten (1974) found recency effects in long-term memory when each item was followed by a distracting task, so that no item could have been held in a short-term buffer at the test. Such long-term recency led to accounts in which the ends of a sequence are favored because they are more distinctive in time: an item’s distance from the moment of recall, relative to its neighbors, makes the first and last items easier to single out (Brown et al., 2007). A recent study that tested the same items immediately and later found recency effects in both working memory and long-term memory but primacy effects only in long-term memory, consistent with the view that the two systems contribute to the curve in partly different ways (Forsberg et al., 2025). Researchers still debate the relative contributions of rehearsal, temporal distinctiveness, and retrieval processes, but the existence of the effect is not in dispute.

Serial Position Beyond Word Lists

The effect appears with material people learned over years rather than minutes. When students were asked to recall the U.S. presidents, recall was highest for the first few and the most recent presidents and lower for those in between, with a notable exception: Abraham Lincoln, in the middle of the sequence, was recalled very well (Roediger & Crowder, 1976). The exception illustrates a point developed in the companion paper on the isolation effect: a distinctive or significant item can be remembered well wherever it falls.

Direct research on serial position in memory for witnessed events is limited, and the extension from lists to events should be made with care. A crime or an accident is not a list of equivalent items. Its middle often contains the most important and emotionally significant action, which may receive more attention than its beginning or end, and people use their knowledge of how such events usually unfold to organize what they recall. The serial position effect therefore supports a modest proposition: uneven memory across a sequence is an ordinary feature of memory and is not, by itself, a sign of fabrication or general unreliability. It does not support a prediction that a particular witness will remember the start and finish of an event better than its middle, or that a particular gap reflects position rather than attention, stress, delay, or other factors.

Position Effects in Lineups

In a sequential lineup, the witness views one person at a time and decides about each before seeing the next. Because the witness cannot compare the whole set at once, the position of the suspect may matter. Carlson et al. (2008) found that the diagnostic value of suspect identifications in sequential lineups increased as the suspect was placed later in the sequence, and that the advantage of sequential over simultaneous lineups appeared only when an innocent suspect stood out from the fillers. Using ROC analysis, which separates the ability to distinguish guilty from innocent suspects from the willingness to choose, Meisters et al. (2018) found that witnesses in sequential lineups applied a strict standard at the earliest positions and a more lenient one at later positions, while no position effects appeared in simultaneous lineups.

The most recent large study points in a somewhat different direction. In two experiments with more than 2,500 participants each, culprits and innocent suspects were assigned at random to every position in six-person simultaneous and sequential photo lineups. Position did not affect witnesses’ ability to detect whether the culprit was present in either format, but in both formats the person in the first position was more likely to be chosen through guessing, and the authors concluded that the findings support the practice of not placing the suspect first (Mayer et al., 2024). Taken together, these studies suggest that position effects in lineups operate at least in part on response tendencies, such as caution or guessing, and that the size and form of the effect depend on lineup format and procedure. Whether simultaneous or sequential lineups are preferable overall is addressed in the companion paper on lineup construction.

Order Effects in Trials: Openings, Evidence, and Closings

Research on how people form judgments from a series of arguments has found both primacy and recency, depending on the task. A model of belief updating proposed that recency tends to occur when people evaluate each piece of evidence as it arrives and the series is short, while primacy becomes more likely with longer series and when judgments are made only at the end (Hogarth & Einhorn, 1992). These are effects on judgment and persuasion rather than on memory, but they bear on the same question of whether order matters.

Several mock-trial studies have tested order directly. In one, the amount of preview offered in the prosecution’s and the defense’s opening statements interacted: an extensive defense opening increased not-guilty verdicts only when the prosecution’s opening was brief, and mid-trial measures indicated that jurors formed an early leaning that they tended to keep, which the authors interpreted as opening statements providing a framework for later evidence (Pyszczynski & Wrightsman, 1981). Mock jurors have also been found more persuaded when a side’s evidence was presented in the chronological order of a story rather than in the order of the witnesses who supplied it (Pennington & Hastie, 1988). Costabile and Klein (2005) reported recency effects in mock-juror judgments, with evidence presented later in a trial exerting more influence. In sentencing experiments with legal professionals, the defense’s recommendation, made after the prosecutor’s, was itself pulled toward the prosecutor’s demand, so that speaking last did not neutralize the influence of the earlier figure (Englich et al., 2005).

The direction of trial order effects is therefore not fixed. Primacy has been found for opening frames and initial anchors, recency for late-arriving evidence in some designs, and story structure appears to matter as much as position. Most of these studies used written or videotaped summaries, short trials, and student or community participants who did not deliberate, and none can say which way order affected a particular verdict.

Limits of the Evidence

The classic serial position findings come from laboratory lists of unrelated words studied by university students over seconds or minutes. They are robust within that setting, but the effect sizes and shapes do not transfer directly to an extended, meaningful, emotionally significant event, for which there is little direct research. Lineup position studies are large and well controlled but mostly online experiments with brief videos and no consequences; they disagree to some extent about the form of the effect, and field data on suspect position are scarce. Mock-trial order studies are older, often small, and inconsistent in direction. Group findings describe average tendencies under particular conditions; they cannot establish that a particular witness’s gap, a particular identification, or a particular verdict was produced by position.

Questions to Ask About This Research

When an expert cites the bowed curve of list recall (Murdock, 1962; Glanzer & Cunitz, 1966) to explain gaps in a witness’s account, counsel should ask what the studies measured, namely recall of unrelated words in lists, and what evidence shows that the pattern holds for a real, extended event whose middle may have contained the most important action. When lineup position research is cited, counsel should ask which outcome is described: Mayer et al. (2024) found that the first position increased guessing-based choices without affecting detection of the culprit, Meisters et al. (2018) found criterion shifts across sequential positions, and Carlson et al. (2008) found that diagnosticity rose with later positions, so counsel should ask whether this lineup was simultaneous or sequential, where the suspect appeared, whether position was randomized and recorded, and whether a stopping rule was used. When trial order research is offered, counsel should ask whether the cited studies found primacy or recency, what kind of participants and trial materials were used, and whether jurors deliberated. These questions are explained in “Reading Research Claims: A Guide for Attorneys” on this site.

The Serial Position Effect and the Law

Federal and Military Standards

Expert testimony about memory is governed by Federal Rule of Evidence 702, as amended December 1, 2023, under which the proponent must show the court that it is more likely than not that the rule’s requirements are met, including that the opinion reflects a reliable application of reliable methods to the case. Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) made the trial judge a gatekeeper, and Kumho Tire Co. v. Carmichael (1999) extended that obligation to all expert testimony, including testimony based on technical or other specialized knowledge. In courts-martial, Military Rule of Evidence 702 tracks the federal rule, the 2023 federal amendment took effect in the military rule in 2025 through Military Rule of Evidence 1102 (Joint Service Committee on Military Justice, 2025), and practitioners should confirm current text; military judges apply the six factors of United States v. Houser (1993). Military Rule of Evidence 321 makes an identification inadmissible on timely objection if it resulted from an identification process so suggestive as to create a substantial likelihood of misidentification. The rule does not address lineup format or suspect position, but where the suspect was placed is one of the circumstances a party may raise in arguing whether a procedure was suggestive. The order of trial is committed to the court: under Federal and Military Rule of Evidence 611(a), the judge exercises reasonable control over the mode and order of examining witnesses and presenting evidence so as to make those procedures effective for determining the truth.

Arizona

Arizona Rule of Evidence 702 adopted the federal formulation and the Daubert standard effective January 1, 2012, and was amended effective January 1, 2024, to conform to the 2023 federal amendment (Ariz. Sup. Ct. Order R-23-0004). State v. Chapple (1983) is Arizona’s leading case on expert testimony about eyewitness memory; excluding such testimony was an abuse of discretion on its facts, while admission otherwise remains within the trial court’s discretion, and State v. Nordstrom (2001) approved limiting an expert to general factors without opinions on the accuracy of a particular witness. Experts may not opine on whether a particular witness is truthful (State v. Lindsey, 1986, 149 Ariz. at 475). A defendant who challenges a pretrial identification procedure may request a hearing under State v. Dessureault (1969), at which the manner in which a lineup was assembled and shown, including the suspect’s position, can be examined, and Arizona’s identification instruction directs jurors to consider the witness’s opportunity to view, degree of attention, the accuracy of any prior description, certainty at the pretrial identification, the time between the crime and that identification, and any other factor affecting reliability (RAJI (Criminal) Standard Criminal 45). Arizona Rule of Evidence 611(a) likewise gives the court control over the order of presenting evidence.

Special Issues in Legal Practice

The principles described above apply with equal force to every party in a legal proceeding. The science operates the same way regardless of who is asking the questions, and the research summarized here does not by itself favor either side. What differs between the parties is not the science but the vantage point — the particular places where these issues tend to surface, and the particular errors each party is best positioned to guard against. The two summaries below identify those recurring issues. They are offered for orientation, not as litigation strategy; in every case the controlling question is what the evidence in that case will, and will not, support, and the expert’s role is to inform the trier of fact rather than to advocate for either side.

Special Issues for Prosecutors

The research supports several propositions prosecutors can legitimately present. Memory for any sequence is uneven, and stronger recall of some parts than others is an ordinary feature of memory rather than, by itself, a sign of fabrication or general unreliability. Distinctive or significant moments can be remembered well wherever they fall in an event. In lineups, the most recent large study found that position affected guessing more than the ability to detect whether the culprit was present, while earlier studies found position effects on diagnosticity or response criterion in sequential lineups, so the findings depend on lineup format; a lineup in which the suspect’s position was randomized and recorded, and not placed first, is better positioned to withstand a position challenge. Prosecutors are well positioned to ensure that position is documented as part of the lineup record.

The research also counsels caution. The serial position literature does not support telling a factfinder that a witness’s memory for a particular part of an event should be strong or weak because of where it fell, and an expert who describes laboratory list findings as a rule for real events goes beyond the evidence. A suspect placed first, or late in a sequential lineup without a record of why, invites a legitimate question about whether position contributed to the choice. Trial order research does not show that presenting the strongest evidence first or last will reliably produce a particular result, and arguments that rely on it as settled overstate what the studies show.

Special Issues for Defense

The research supports several propositions defense counsel can legitimately present. Where an item falls in a sequence can affect whether it is recalled and how it is judged, and in lineups position can affect a witness’s willingness to choose, particularly the tendency to select the first person shown and the shift in caution across a sequential lineup. Evidence of where the suspect appeared, whether position was randomized, and whether the procedure used a stopping rule is a legitimate basis for examining an identification, and expert testimony that explains these findings in general terms can help the factfinder evaluate it.

The research also counsels caution about the limits that apply to the defense. In the most recent large study position mainly affected guessing rather than detection of the culprit, earlier studies found effects on diagnosticity or criterion, and none of them can show that a particular identification resulted from position. Laboratory list findings do not establish that a witness’s account of the middle of an event is unreliable, and uneven recall does not by itself impeach a witness. Trial order effects run in both directions, so they do not support a general claim that the order of proof disadvantaged the accused, and the same principles apply to the accused’s own account of a sequence of events.

This paper is for educational purposes only and is not legal advice. The author is a psychologist, not an attorney; summaries of law are general and must be verified against current authority or with a licensed attorney.

References

Atkinson, R. C., & Shiffrin, R. M. (1968). Human memory: A proposed system and its control processes. In K. W. Spence & J. T. Spence (Eds.), The psychology of learning and motivation (Vol. 2, pp. 89–195). Academic Press. https://doi.org/10.1016/S0079-7421(08)60422-3

Bjork, R. A., & Whitten, W. B. (1974). Recency-sensitive retrieval processes in long-term free recall. Cognitive Psychology, 6(2), 173–189. https://doi.org/10.1016/0010-0285(74)90009-7

Brown, G. D. A., Neath, I., & Chater, N. (2007). A temporal ratio model of memory. Psychological Review, 114(3), 539–576. https://doi.org/10.1037/0033-295X.114.3.539

Carlson, C. A., Gronlund, S. D., & Clark, S. E. (2008). Lineup composition, suspect position, and the sequential lineup advantage. Journal of Experimental Psychology: Applied, 14(2), 118–128. https://doi.org/10.1037/1076-898X.14.2.118

Costabile, K. A., & Klein, S. B. (2005). Finishing strong: Recency effects in juror judgments. Basic and Applied Social Psychology, 27(1), 47–58. https://doi.org/10.1207/s15324834basp2701_5

Deese, J., & Kaufman, R. A. (1957). Serial effects in recall of unorganized and sequentially organized verbal material. Journal of Experimental Psychology, 54(3), 180–187. https://doi.org/10.1037/h0040536

Englich, B., Mussweiler, T., & Strack, F. (2005). The last word in court—A hidden disadvantage for the defense. Law and Human Behavior, 29(6), 705–722. https://doi.org/10.1007/s10979-005-8380-7

Forsberg, A., Guitard, D., Greene, N. R., Naveh-Benjamin, M., & Cowan, N. (2025). Differential information transfer and loss between working memory and long-term memory across serial positions. Journal of Experimental Psychology: Learning, Memory, and Cognition, 51(8), 1191–1212. https://doi.org/10.1037/xlm0001437

Glanzer, M., & Cunitz, A. R. (1966). Two storage mechanisms in free recall. Journal of Verbal Learning and Verbal Behavior, 5(4), 351–360. https://doi.org/10.1016/S0022-5371(66)80044-0

Hogarth, R. M., & Einhorn, H. J. (1992). Order effects in belief updating: The belief-adjustment model. Cognitive Psychology, 24(1), 1–55. https://doi.org/10.1016/0010-0285(92)90002-J

Joint Service Committee on Military Justice. (2025). Amendments to the Military Rules of Evidence since 1984 (G. E. Maggs, Ed.; 2025 ed.). https://jsc.defense.gov/Portals/99/MRE%20Amendments%202025.pdf

Mayer, C., Bell, R., Menne, N. M., & Buchner, A. (2024). Lineup position affects guessing-based selection but not culprit-presence detection in simultaneous and sequential lineups. Scientific Reports, 14, Article 27642. https://doi.org/10.1038/s41598-024-78936-9

Meisters, J., Diedenhofen, B., & Musch, J. (2018). Eyewitness identification in simultaneous and sequential lineups: An investigation of position effects using receiver operating characteristics. Memory, 26(9), 1297–1309. https://doi.org/10.1080/09658211.2018.1464581

Murdock, B. B., Jr. (1962). The serial position effect of free recall. Journal of Experimental Psychology, 64(5), 482–488. https://doi.org/10.1037/h0045106

Pennington, N., & Hastie, R. (1988). Explanation-based decision making: Effects of memory structure on judgment. Journal of Experimental Psychology: Learning, Memory, and Cognition, 14(3), 521–533. https://doi.org/10.1037/0278-7393.14.3.521

Pyszczynski, T. A., & Wrightsman, L. S. (1981). The effects of opening statements on mock jurors’ verdicts in a simulated criminal trial. Journal of Applied Social Psychology, 11(4), 301–313. https://doi.org/10.1111/j.1559-1816.1981.tb00826.x

Roediger, H. L., III, & Crowder, R. G. (1976). A serial position effect in recall of United States presidents. Bulletin of the Psychonomic Society, 8(4), 275–278. https://doi.org/10.3758/BF03335138

Rundus, D. (1971). Analysis of rehearsal processes in free recall. Journal of Experimental Psychology, 89(1), 63–77. https://doi.org/10.1037/h0031185

Legal Authorities

Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).

Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999).

State v. Chapple, 135 Ariz. 281, 660 P.2d 1208 (1983).

State v. Dessureault, 104 Ariz. 380, 453 P.2d 951 (1969).

State v. Lindsey, 149 Ariz. 472, 720 P.2d 73 (1986).

State v. Nordstrom, 200 Ariz. 229, 25 P.3d 717 (2001).

United States v. Houser, 36 M.J. 392 (C.M.A. 1993).

Fed. R. Evid. 611.

Fed. R. Evid. 702.

Mil. R. Evid. 321.

Mil. R. Evid. 611.

Mil. R. Evid. 702.

Mil. R. Evid. 1102.

Ariz. R. Evid. 611.

Ariz. R. Evid. 702.

Ariz. Sup. Ct. Order R-23-0004 (amending Ariz. R. Evid. 702, effective Jan. 1, 2024).

Revised Arizona Jury Instructions (Criminal), Standard Criminal 45 (Identification) (6th ed. 2022).

Related topics from Arizona Forensic Services: Courts-Martial