Snap Shot
- The question: When a witness says an event happened at a particular time, or a particular number of times within a period, how accurate is that dating likely to be, and in which direction are errors likely to run?
- What the research shows: People rarely store the date of an event; they reconstruct it, and errors grow with the age of the event. Remote events tend to be dated as more recent than they were (forward telescoping), recent events are sometimes dated as more remote (backward telescoping), and counts within a bounded period tend to be inflated when outside events are pulled in. Dating tied to known dates and temporal landmarks, and dating given with higher confidence, tends to be more accurate.
- What it does not show: Telescoping concerns when an event happened, not whether it happened; a dating error is not, by itself, evidence that the event did not occur or that the witness is untruthful, and the research cannot say whether any particular dating error reflects ordinary memory error. The point at which forward bias gives way to backward bias varies with the time span and method, so no fixed figure applies to a witness.
- The law: Expert testimony is governed by Rule 702, Houser, and in Arizona by Rule 702, Chapple, and Nordstrom. In courts-martial, “on or about” allows proof of a reasonably near date (Hunt; Simmons), and proof outside the pleaded period raises variance and factual sufficiency questions (Teffeau; Kershaw); Arizona permits amendments that correct mistakes of fact or technical defects without changing the offense (Ariz. R. Crim. P. 13.5(b); Freeney).
- Issues for each side: Prosecutors can explain that dating errors are common even in witnesses who are accurate about what happened, although their presence or absence does not by itself show whether a witness is accurate, and should anchor dates to records and landmarks rather than to unaided estimates; defense counsel can test dates and counts against independent evidence without treating a dating error as proof that an event did not occur.
Testimony about an event usually includes testimony about its timing: how long ago it occurred, whether it preceded or followed some other event, and how often it recurred within a period. Charges are framed around dates and date ranges, limitation periods are measured from them, and alibis depend on them. The telescoping effect is a systematic error in these judgments. Placing a distant event closer to the present than it actually was is known as forward telescoping; placing a recent event further in the past than it actually was is known as backward telescoping.
A complainant may place an incident in the wrong school year, or a count of incidents “in the last year” may include earlier ones. Such discrepancies are often argued to show unreliability or fabrication. The research explains why they arise in sincere and otherwise accurate witnesses and identifies the conditions under which dating is more and less trustworthy.
This paper covers how people date past events, why dating errors are systematic, telescoping in surveys and counts, landmarks and repeated events, age differences, the limits of the research, and the law on charging dates and variance. The broader effects of long delays are covered in Delayed Recall.
How People Date Past Events
Memories rarely carry a date. Reviews of research on memory for time conclude that people usually reconstruct when something happened from surrounding information, such as the season, what else was happening in their lives, the school year or job they were in, and their general knowledge of how time is organized (Friedman, 1993). A witness may be accurate about what happened and mistaken about when.
In studies in which people dated personal or public events whose true dates were known from diaries, records, or news archives, errors of months or years were common for older events, and the size of the error grew with the time since the event (Brown et al., 1985; Thompson et al., 1988). Brown et al. (1985) also found that public events about which people knew more were dated as more recent than events about which they knew less, consistent with the idea that people use how easily an event comes to mind as a cue to how recent it was.
The format of the question matters. When participants dated news events, estimates given as calendar dates (“July 2004”) were more accurate than estimates given as elapsed time (“three weeks ago”), and the same study found a small backward telescoping effect for recent news events and a large forward telescoping effect for remote ones (Janssen et al., 2006). Changing how survey and laboratory questions were posed changed the amount of forward telescoping in participants’ answers, which the authors attributed to whether the question prompted people to retrieve information about when the events occurred (Prohaska et al., 1998).
Why Dating Errors Are Systematic
A common intuition is that time is simply compressed in memory, so that everything seems closer than it was. Rubin and Baddeley (1989) proposed a model that does not require any systematic compression. In their account, three ordinary features of memory are enough to produce forward telescoping when people are asked what happened within a defined period: recent events are retained better than older ones; dating errors, though not biased in either direction, grow larger with the age of the event; and events from outside the period can intrude into it, but events that have not yet happened cannot. In their studies, psychologists’ errors in dating colloquia grew steadily with the delay and tended to fall toward the middle of the period asked about, so that older events were pulled forward and recent ones pushed back.
Other mechanisms contribute. In a study of date estimates for 64 news events, removing guesses greatly reduced backward telescoping but left forward telescoping unchanged, suggesting that different biases have different causes (Lee & Brown, 2004). The practical point does not depend on which model is correct: dating errors are common, they grow with time, and for remote events their net direction in most studies is toward the present.
Statements that forward telescoping takes over beyond a fixed interval, such as three years, are not supported by a single established figure. The point at which errors change direction depends on the span of time being asked about and on the events and methods studied. In one study of children dating their own early memories, for example, memories from before about age four were dated as more recent than they were, and later memories were dated as earlier than they were (Wang et al., 2010).
Telescoping in Surveys and Counts
Survey researchers identified the practical consequences of telescoping decades ago. In household interviews about home repair expenditures, respondents who were asked about a recent period without a prior interview to mark its start reported substantially more expenditures for that period than respondents whose earlier interview “bounded” it, a difference attributed largely to expenditures from before the period being reported as falling within it (Neter & Waksberg, 1964). Bounded interviewing became a standard tool for reducing telescoping in surveys, including crime victimization surveys.
Landmarks serve a similar function. In a classic study, asking people about victimization since a memorable public event, rather than within a stated number of months, reduced the number of incidents they reported, consistent with a reduction in forward telescoping (Loftus & Marburger, 1983). Reports of when something began are affected too: in a large national survey, people of the same birth year reported later ages of first smoking the older they were when interviewed, indicating that onset was displaced toward the interview (Johnson & Schultz, 2005).
The forensic parallel is direct: incidents from before a charged period can be drawn into a witness’s count for that period, and a first occasion may be placed later than it was. Neither error implies that the incidents did not occur.
Landmarks, Repeated Events, and Indicators of Accuracy
Dating is generally more accurate when an event can be linked to something with a known date. In two studies in which partners’ diaries or records were used to verify the dates of participants’ personal events, dates were more accurate when the participant used a strategy based on known dates and when the event was directly connected to a temporal landmark, such as a holiday or a move; for both recent events (3 to 11 weeks old) and remote events (3 to 5 years old), higher confidence in a date was associated with greater dating accuracy in those studies (Neusar & Rubínová, 2023; see “Confidence and Accuracy” for confidence in identifications). The finding cuts both ways: a confident date tied to a landmark generally deserves more weight than a bare estimate, and a date tied to nothing deserves less.
Repeated events present a special difficulty. Many cases involve a series of similar incidents, and the occasions in such a series often lack distinctive markers that would allow each one to be dated. In an analysis of six studies of memory for repeated events, details were confused between instances more often for middle instances than for the first and last, and most often between neighboring instances (Rubínová & Kontogianni, 2023). That analysis concerned confusion of details between instances, not dating; the inference that the first and last occasions, and occasions linked to a distinctive circumstance, are therefore more likely to be dated accurately than an occasion in the middle of a series is the author’s, and the analysis did not test it. The companion paper, Episodic Memory, discusses how memory for repeated events bears on charging and findings.
Age and Individual Differences
Dating accuracy varies across the lifespan, though not simply. In studies of the dating of public events, adults aged 35 to 50 dated events more accurately than university students and adults over 60; forward telescoping decreased with age, and in one study adults over 60 tended to date events as more remote than they were (Crawley & Pring, 2000). The direction of error may therefore differ for older witnesses.
Children’s dating of their own memories is also systematically biased. In a study of 344 Chinese and European Canadian children aged 8, 11, and 14, whose parents verified the events and the children’s ages at the time, earlier memories were dated as more recent than they were and later memories as earlier than they were, and the pattern changed with age (Wang et al., 2010). The study concerned events before school entry recalled years later, not recent events or events linked to a grade, a holiday, or a move; for young witnesses, the grade, home, or season to which a child links an event may be more informative than a calendar date.
Limits of the Evidence
Most telescoping research involves news events, diary events, survey questions about purchases and medical visits, or laboratory sessions, usually with adults dating events of modest importance, and it measures accuracy across many events rather than for any single date. Research on children dating their own memories is small. Little research addresses the dating of traumatic events, of events later discussed in investigative interviews, or by witnesses who have discussed dates with others. The size of dating error varies widely across individuals, events, and methods, and no study supplies an error rate that can be applied to one witness’s date. Telescoping research measures where people place events in time; it does not measure whether events occurred.
Questions to Ask About This Research
When Rubin and Baddeley (1989) or Janssen et al. (2006) is cited to show that a witness’s date is likely displaced toward the present, counsel should ask who was studied and what was dated: psychologists dating colloquia and adults dating news events are not witnesses dating a personal incident. When a count of incidents within a charged period is said to be inflated, counsel should ask whether the witness’s account offers a boundary, such as a move or a school year, that would reduce intrusions from outside the period, because bounding and landmarks reduce telescoping (Neter & Waksberg, 1964; Loftus & Marburger, 1983). When Neusar and Rubínová (2023) is cited to support a confident, landmark-linked date, counsel should ask whether the conclusion follows for this witness, since the association between confidence and dating accuracy was measured across many events and participants and does not establish that a particular confident date is correct. When Wang et al. (2010) is cited about a child, counsel should ask whether the events at issue resemble the early childhood memories studied. These questions are explained in “Reading Research Claims: A Guide for Attorneys” on this site.
Telescoping and the Law
Federal and Military Standards
Expert testimony about dating errors 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 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; under Military Rule of Evidence 1102, the Joint Service Committee’s 2025 compilation reflects the 2023 amendment as part of the military rule (Joint Service Committee on Military Justice, 2025), and practitioners should confirm current text. Military judges also apply the six factors of United States v. Houser (1993).
Dates matter most in pleading and proof. The Discussion accompanying Rule for Courts-Martial 307(c)(3), which is guidance rather than binding rule, advises that the date be stated precisely enough to identify the offense and to let the accused understand what to defend against, that alleging “on or about” a specified day is proper, and that conduct extending over a considerable period may be alleged as occurring from about one date to about another or “on divers occasions” between two dates (2024 edition; practitioners should confirm current text). “On or about” means that the government need not prove the exact date if it proves a reasonably near one (United States v. Hunt, 1993), and the Court of Appeals for the Armed Forces has described the phrase as connoting a range of days to weeks (United States v. Simmons, 2022). When the proof falls outside the pleaded period, the question becomes one of variance, which requires reversal only if the variance is material and substantially prejudices the accused, for example by misleading the accused or exposing the accused to a second prosecution (United States v. Teffeau, 2003). In United States v. Kershaw (2026), a child sexual abuse case in which the conduct was pleaded within a single month but the timeline at trial had to be reconstructed from past residences and personal events, the Air Force Court of Criminal Appeals placed the offense six months to a year earlier and set the finding aside as factually insufficient. A divided (3–2) Court of Appeals for the Armed Forces held that a Court of Criminal Appeals must first ask whether the proven date falls within the “on or about” range and, if it does not, may conduct a variance analysis and test for prejudice even if the members made no exceptions or substitutions, and it remanded for a new factual sufficiency review; in 2025 it had affirmed an Air Force Court of Criminal Appeals finding of factual insufficiency resting on a date discrepancy, holding that it lacked authority to review that determination (United States v. Patterson, 2025). Limitation periods under Article 43, UCMJ, are treated in Delayed Recall, and “divers occasions” charging in Episodic Memory.
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; exclusion of the expert was an abuse of discretion on its facts, and admission otherwise remains within the trial court’s discretion (State v. Nordstrom, 2001). Experts may not opine on whether a particular witness is truthful (State v. Lindsey, 1986, 149 Ariz. at 475). Without the defendant’s consent, a charge may be amended only to correct mistakes of fact or remedy formal or technical defects, not to change the nature of the offense (Ariz. R. Crim. P. 13.5(b)), and a violation of the rule is not structural error; it is reviewed for prejudice, with attention to whether the defendant had actual notice of the charge (State v. Freeney, 2009). For continuous sexual abuse of a child, A.R.S. § 13-1417 requires three or more qualifying acts over a period of three months or more, so the time span of the conduct is itself in issue, and limitation periods under A.R.S. § 13-107 make dates decisive for offenses that are not exempt from them.
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 points prosecutors can legitimately present. People reconstruct dates rather than retrieve them, dating errors grow with time, and misplacing an event by months, or misordering closely spaced incidents, is common even in witnesses who are accurate about what happened; the presence or absence of such errors does not by itself show whether a witness is accurate. The research also indicates when dates are more trustworthy: dates tied to known dates and temporal landmarks, and dates given with higher confidence in those studies, tend to be more accurate, and, in one analysis of repeated events, details of the first and last incidents of a series were less often confused with other incidents than details of middle ones (Rubínová & Kontogianni, 2023), a finding about confusion of details rather than dates. Prosecutors are well positioned to reduce dating error by asking witnesses to link events to landmarks such as a grade, a residence, a deployment, or a holiday, by recording how a date was arrived at, and by drafting date ranges the account and records support.
The research also counsels caution. Because remote events tend to be pulled toward the present and counts within a period tend to be inflated by intrusions from outside it, a charge that depends on a precise date, a precise count, or the timing of the first occasion may rest on the part of an account most prone to error. Confidence in a date that may have been suggested by an interviewer or a charging document does not corroborate it, and school, medical, travel, and duty records are the strongest check on a timeline.
Special Issues for Defense
The research supports several points defense counsel can legitimately present. Dates are reconstructions, errors grow with time, remote events are generally displaced toward the present, and counts for a bounded period can be inflated by events from outside it. Elapsed-time estimates are generally less accurate than dates tied to landmarks, and middle occasions in a series are especially hard to place. Defense counsel are well positioned to examine how each date in an account was arrived at, whether it was suggested or anchored by an interviewer, and whether it can be reconciled with independent records, which bears on alibi, on limitation periods, and on whether the proof matches the pleaded dates.
The research also counsels caution. Telescoping is an error in placing events in time, not evidence that an event did not occur, and arguments that treat a misdated or misordered incident as a sign of fabrication go beyond the research. A witness who misdates an event may be accurate about what happened, a confident date tied to a landmark is on average more likely to be accurate, and an expert may describe the conditions under which dating errors occur but may not tell the factfinder that a particular witness’s date, or account, is mistaken.
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
Brown, N. R., Rips, L. J., & Shevell, S. K. (1985). The subjective dates of natural events in very-long-term memory. Cognitive Psychology, 17(2), 139–177. https://doi.org/10.1016/0010-0285(85)90006-4
Crawley, S. E., & Pring, L. (2000). When did Mrs Thatcher resign? The effects of ageing on the dating of public events. Memory, 8(2), 111–121. https://doi.org/10.1080/096582100387650
Friedman, W. J. (1993). Memory for the time of past events. Psychological Bulletin, 113(1), 44–66. https://doi.org/10.1037/0033-2909.113.1.44
Janssen, S. M. J., Chessa, A. G., & Murre, J. M. J. (2006). Memory for time: How people date events. Memory & Cognition, 34(1), 138–147. https://doi.org/10.3758/BF03193393
Johnson, E. O., & Schultz, L. (2005). Forward telescoping bias in reported age of onset: An example from cigarette smoking. International Journal of Methods in Psychiatric Research, 14(3), 119–129. https://doi.org/10.1002/mpr.2
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
Lee, P. J., & Brown, N. R. (2004). The role of guessing and boundaries on date estimation biases. Psychonomic Bulletin & Review, 11(4), 748–754. https://doi.org/10.3758/BF03196630
Loftus, E. F., & Marburger, W. (1983). Since the eruption of Mt. St. Helens, has anyone beaten you up? Improving the accuracy of retrospective reports with landmark events. Memory & Cognition, 11(2), 114–120. https://doi.org/10.3758/BF03213465
Neter, J., & Waksberg, J. (1964). A study of response errors in expenditures data from household interviews. Journal of the American Statistical Association, 59(305), 18–55. https://doi.org/10.1080/01621459.1964.10480699
Neusar, A., & Rubínová, E. (2023). When did this happen? Indicators of accuracy for dating recent and remote personal events. Journal of Applied Research in Memory and Cognition, 12(2), 290–304. https://doi.org/10.1037/mac0000065
Prohaska, V., Brown, N. R., & Belli, R. F. (1998). Forward telescoping: The question matters. Memory, 6(4), 455–465. https://doi.org/10.1080/741942604
Rubin, D. C., & Baddeley, A. D. (1989). Telescoping is not time compression: A model of the dating of autobiographical events. Memory & Cognition, 17(6), 653–661. https://doi.org/10.3758/BF03202626
Rubínová, E., & Kontogianni, F. (2023). Sources and destinations of misattributions in recall of instances of repeated events. Memory & Cognition, 51(1), 188–202. https://doi.org/10.3758/s13421-022-01300-7
Thompson, C. P., Skowronski, J. J., & Lee, D. J. (1988). Telescoping in dating naturally occurring events. Memory & Cognition, 16(5), 461–468. https://doi.org/10.3758/BF03214227
Wang, Q., Peterson, C., & Hou, Y. (2010). Children dating childhood memories. Memory, 18(7), 754–762. https://doi.org/10.1080/09658211.2010.508749
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. Freeney, 223 Ariz. 110, 219 P.3d 1039 (2009).
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).
United States v. Hunt, 37 M.J. 344 (C.M.A. 1993).
United States v. Kershaw, No. 25-0177/AF (C.A.A.F. Apr. 30, 2026).
United States v. Patterson, 86 M.J. 24 (C.A.A.F. 2025).
United States v. Simmons, 82 M.J. 134 (C.A.A.F. 2022).
United States v. Teffeau, 58 M.J. 62 (C.A.A.F. 2003).
10 U.S.C. § 843 (Article 43, Uniform Code of Military Justice).
Ariz. Rev. Stat. Ann. § 13-107.
Ariz. Rev. Stat. Ann. § 13-1417.
Fed. R. Evid. 702.
Mil. R. Evid. 702.
Mil. R. Evid. 1102.
R.C.M. 307(c)(3) & Discussion, Manual for Courts-Martial, United States (2024 ed.).
Ariz. R. Evid. 702.
Ariz. R. Crim. P. 13.5.
Ariz. Sup. Ct. Order R-23-0004 (amending Ariz. R. Evid. 702, effective Jan. 1, 2024).
Related topic papers: Delayed Recall · Episodic Memory · Autobiographical Memory · Reconstruction and Recall · Forgetting · Suggestibility of Children’s Memory
Related topics from Arizona Forensic Services: Child Abuse Allegations · Courts-Martial