Why do some things “seem like they just happened yesterday?”


The Telescoping Effect

, explained.

What is Telescoping Effect?

The telescoping effect refers to inaccurate perceptions regarding time, where people see recent events as more remote than they are (backward telescoping), and remote events as more recent (forward telescoping). This mental error in memory can occur whenever we make temporal assumptions regarding past events.

Where it occurs

It seems every year, on September 11, people remark how 9/11 seems like it wasn’t that long ago, and are surprised to hear the media highlight the number of years that have actually passed since the tragedy. Conversely, a few months into the COVID-19 pandemic and one might feel a lot more time has passed than it has. Instances of forward telescoping however, such as the case with 9/11, are more common than backward telescoping.1

These misjudgments in time stem from our tendency to assess remembered events by how long ago it feels they occurred rather than a deliberate calculation. Although it’s easier to spot these memory mix-ups in other people, they’re not always easy to detect in ourselves.

Individual effects

Although these memory lapses seem rather innocuous, the ramifications of the telescoping effect can be significant. Consider a casual investor who may mistime the market because of misperceptions of when certain events actually took place. This person might think back to an interview they watched on Bloomberg, where a guest was talking about a promising stock that’s undervalued. It feels like just last week they watched this interview, and they decide to buy the stock. It turns out however, that the interview was actually three months ago and much of the hype has already been priced into the stock.


Systemic effects

Systemic telescoping can greatly affect market research. Many surveys that are used to make key decisions in business, politics, and science, rely on survey data that often ask respondents something like: “In the past six months, how often have you?…” Under the scenario where a number of respondents succumbed to the telescoping effect in their recollections, organizations may be making decisions or inputting forecasts based on inaccurate data.

While it may seem that the telescoping effect may just add “noise” to a given data set, research has suggested that on average, respondents are misestimating time intervals. A study from the late-90’s found consumers to be quite inaccurate in recalling the period when they had purchased a computer.2 An overall forward telescoping effect was found, where respondents believed they had bought a computer more recently than they had.

Why it happens

One theory behind the telescoping effect is the accessibility principle, where time perceptions regarding certain events depend on how accessible information is for that event.3 The more that is known and easily accessed in immediate memory, the more recent it seems. 9/11 for example, is a very salient memory for many people, as they can often vividly recall what they were doing at the time and how they felt. This level of accessibility results in forward telescoping by creating a feeling that the event was fairly recent. On the other hand, after an eventful weekend, we might say on Monday that Friday “feels like forever ago,” with such backward telescoping stemming from a more congested short-term memory where all the things that happened on the weekend blur recollection of Friday, making it less accessible.

With forward telescoping being the predominant form of telescoping, the accessibility principle seems like a logical explanation and one that runs parallel to other cognitive errors, such as the availability heuristic, where information that is more easily accessed in memory and is thus more salient, affects our perception of that information.

It’s important to keep in mind however, that there is little consensus surrounding the mechanisms behind the telescoping effect, with some suggesting that the bias is not necessarily due to a fundamental cognitive error, such as the accessibility principle, but by a combination of factors.4

Why it is important

Decisions where knowing the elapsed time is a key factor can be subjected to bias from the telescoping effect. Mitigating the reliance on inaccurate assessments of time will strengthen decision-making and add clarity to the subject at hand. Furthermore, while the telescoping effect highlights our own potential risks when recalling when events had occurred, it is also a critical element to consider in data collection that relies on self-report responses subject to perceptions of time.

How to avoid it

When making predictions of the future based on events of the past, it’s important to actually look at the numbers. For example, if an R&D manager believes their team should explore new features to match a competitor who “has been launching a lot of new features recently,” it would help to reference the data on exactly when these features were launched and base decisions going forward on concrete information rather than intuition.

As a market researcher, when designing a survey that is attempting to probe a respondent’s recollection of a purchase, for example, it might be worthwhile to suggest referencing their email or credit card statement to increase the likelihood of getting accurate data from the respondent. Fortunately, due to modern technology, most people have this information at their fingertips.

How it all started

In 1868, long before cognitive biases were uncovered, the German physiologist Karl von Vierordt published Der Zeitsinn nach Versuchen (The Experimental Study of the Time Sense), a book reporting a number of experiments on the psychology of time perception. From this 19th century piece of scientific literature emerged Vierordt’s Law: That people tend to underestimate the length of long time intervals while overestimating the length of short ones.

While Vierordt’s Law continued to be investigated within the scientific community, it wasn’t until 1964, roughly a century after Vierordt’s pioneering book, that the central idea branched off into what we now refer to as the telescoping effect, following a paper by John Neter and Joseph Waksberg titled, A Study of Response Errors in Expenditures Data from Household Interviews.5

While general memory mix-ups related to Vierordt’s work continue to be explored in a variety of forms, the telescoping effect that first emerged from Neter and Waksberg 1964 paper–as its publication in the Journal of the American Statistical Association might suggest–predominately relates to research methodologies and paradigms, as the telescoping effect has considerable implications in marketing and public health research that rely on respondent estimations of time durations.

Example 1 - How long have you been smoking?

There is a breadth of research in the telescoping realm that explores an effect within the age of onset for the use of recreational substances such as drugs and alcohol. For example, one study found a forward telescoping effect among cigarette, alcohol, and marijuana users.6 The longitudinal data set, collected in “waves” over 8 years, found consistent self-reporting of the age of onset in only a third of marijuana users, with even less consistency among alcohol and cigarette users.

Researchers of such studies argue that the results are important to decision-makers within the public health arena, as efforts at targeting certain youth populations in order to optimize preventative measures often start from self-report data on usage and age of onset, among other factors.

Example 2 - “It seems like only yesterday”

We hear this phrase in a variety of settings: when one is graduating college and thinks back to their first day of class; on an anniversary and a couple recalls their wedding day; during a milestone event for a child and a parent thinks back to when they were a baby.

These moments of reminiscence are unique in that we acknowledge how much time has actually passed, but we still remark how it feels as if that time is shorter than it actually is. As the accessibility principle would suggest, many of these “it seems like only yesterday” moments are in relation to very salient memories, creating a forward telescoping effect as those moments are more accessible in memory.


What it is

The telescoping effect refers to misperceptions regarding time, where people may think events occurred more recently (forward telescoping), or more distantly (backward telescoping) than they actually did.

Why it happens

Although there is no scientific consensus on the bias, some researchers attribute the telescoping effect to the accessibility principle, where perceptions of time in relation to certain events depend on how accessible information is in one’s memory.

Example 1 – How long have you been smoking?

A number of research papers on the telescoping effect have explored the implications of faults in self-reporting related to public health efforts aimed at combating substance abuse. The age of onset for certain substances, which has been shown to be susceptible to the telescoping effect, is an important data point in understanding substance usage.

Example 2 – “It seems like only yesterday”

This nostalgic comment often manifests in a form of forward telescoping, whereby recalling a distant but vivid memory, the moment we’re thinking back on seems more recent than it is.

How to avoid it

On an individual level, if knowing the provenance of an event in memory is an important factor in making a decision, it’s helpful to reference data whenever possible instead of relying on your hunch in regard to when an event occurred.

From a survey design perspective, it may be worthwhile to frame questions in a way that can guide the respondent in providing an accurate response. Blind faith in taking survey responses at face value can neglect the impact of potential cognitive biases such as the telescoping effect.

Related TDL articles

Increasing Trust and Reducing Perception of Waiting Time Through Music

This case study does not directly relate to the telescoping effect, but lies within the realm of time perception and how behavioral science techniques can be used to influence people’s beliefs over how much time has passed.

Time is Money: How Mental Accounting May Influence What we Spend our Time on

If you’re interested in behavioral science ideas around how individuals perceive time, and in other biases and heuristics, like the telescoping effect, that guide our cognition around time, then this piece might be of interest to you!


  1. Lavrakas, P. J. (2008). Encyclopedia of survey research methods (Vols. 1-0). Thousand Oaks, CA: Sage Publications, Inc. doi: 10.4135/9781412963947
  2. Morwitz, V. G. (1997). It seems like only yesterday: The nature and consequences of telescoping errors in marketing research. Journal of Consumer Psychology, 6(1), 1-29.
  3. 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.
  4. Rubin, D. C., & Baddeley, A. D. (1989). Telescoping is not time compression: A model. Memory & Cognition, 17(6), 653-661.
  5. 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.
  6. Shillington, A. M., Woodruff, S. I., Clapp, J. D., Reed, M. B., & Lemus, H. (2012). Self-reported age of onset and telescoping for cigarettes, alcohol, and marijuana: Across eight years of the national longitudinal survey of youth. Journal of child & adolescent substance abuse, 21(4), 333-348.