Research Review: Zechmeister & Shaughnessy (1980)

Here’s the title of the research article:

When you know that you know and when you think that you know but you don’t.

Great title. Much more colorful than most academic research articles. The thing for us to realize is that the "you" in the title of this classic research study is OUR LEARNERS. Sometimes our learners can become overly optimistic about their ability to remember. Oh no. If we believe—even a little bit—the adult-learning-theory mantra that our learners always know best (an incorrect assumption by the way), then we might be setting our learners up for failure.

The research these folks did was designed to look at the spacing effect, the finding that widely-spaced repetitions are more effective than narrowly-spaced repetitions. As the authors say, the spacing effect "has been obtained in a wide variety of memory paradigms, suggesting that it reflects the operation of a fundamental property of the memory system."

Here’s What They Did

They had people study lists of words some of which were repeated. They repeated some of the words immediately and some of them after 3 to 5 other words. Notice that the spacings we’re talking about here are rather small. For some of the words, they asked the subjects to rate how likely they would be to remember the words if asked about them later.

Here’s What They Found

  1. Learners were pretty good at estimating which words they would be able to recall. The one’s they rated most likely to recall, they recalled 66% of the time on a later test. The one’s they rated least likely to recall, they recalled only 35% of the time.
  2. Learners recalled words they were asked to rate better than words they were not asked to rate. Rated words were recalled 52% of the time, non-rated words were recalled 40% of the time. This shows that extra processing, especially meaningful processing, improves learning results. Learners had an extra six seconds per word to do the rating.
  3. Learners recalled repeated items better than items that were not repeated. This is the repetition effect. Non-repeated items were recalled 39% of the time. Repeated items were recalled 49% of the time.
  4. Perhaps what is most intriguing about the data is that narrowly-spaced repetitions gave learners greater confidence (that they would be able to recall a particular word) than widely-spaced repetitions, BUT they actually recalled narrowly-spaced repetitions less highly than the widely-spaced repetitions. Narrowly-spaced repetitions were recalled at a rate of 49% compared with widely-space repetitions, which were recalled at a rate of 62%.

Zeichmeister_shaughnessy_1980_1 Is This Study Relevant to Me?

This is the generalizability question. Although the research had learners study words in a free-recall experimental design, instead of using complex knowledge in a more ecologically valid cued-recall design (real-world memory retrieval is almost always cued recall), there is no reason to think that the research results aren’t widely applicable. The spacing effect is one of the most replicated phenomenon in learning research. Widely-spaced repetitions minimize forgetting, whereas immediate repetitions cannot. And because the spacing effect is such a fundamental learning mechanism, the college-student-as-subject problem is not relevant.

Zeichmeister_shaughnessy_1980_lines_3 Practical Recommendations

  1. Repeat key learning points.
  2. Use spaced repetitions when logistically possible. Even these short spacings made a big difference in the learning results.
  3. Consider prompting your learners to do additional processing of key learning points, especially if that processing is meaningful.
  4. Challenge your learners (within reason) by showing them that their memory is fallible, and that forgetting is likely if they avoid additional learning time.


Zechmeister, E. B., & Shaughnessy, J. J. (1980). When you know that you know and when you think that you know but you don’t. Bulletin of the Psychonomic Society, 15(1), 41-44.