Before Cairo Wakes

Reading it again is the most comfortable way to forget it

A father sits with his son the night before an exam. The boy reads the chapter, then reads it again, then a third time. He closes the book and says, calmly, that he knows it. Two weeks later almost nothing is left. The father assumes his son did not really work. But he did work. He worked for four hours, and he used the worst method available.

Almost everyone does this. Read it again. Highlight it. Read the highlighted parts again. It feels like the material is going in. That feeling is the problem.

The idea, and where it comes from

It is called the testing effect, or retrieval practice. The plain version is this. Pulling something out of your memory does more to fix it there than putting it in again.

Arthur Gates found a version of it in 1917 and it was largely forgotten for most of a century. The modern proof came in 2006, when Henry Roediger and Jeffrey Karpicke of Washington University in St Louis published two experiments in the journal Psychological Science. Their results are unusually clean, so it is worth going through the actual numbers rather than the slogan.

What they did, and what happened

In the first experiment 120 students read short science passages, about 260 words each. Every passage was broken into 30 units of meaning so recall could be scored properly. Then the students either read the passage a second time, or sat a blank sheet test and wrote down everything they could remember, with no feedback and no correct answers shown.

Five minutes later, the rereaders won. They recalled 81 percent against 75 percent for the tested group. If the exam had been that afternoon, rereading was the right choice.

Two days later it had flipped. Tested 68 percent, rereaders 54 percent. One week later, tested 56 percent, rereaders 42 percent.

The second experiment is the one that should change how you study anything. 180 students. One group read the passage four times and never tested. A second read it three times and tested once. A third read it once and tested three times.

The researchers counted how many times each group actually got through the text. The heavy readers went through it 14.2 times. The testing group went through it 3.4 times, roughly a quarter as much exposure.

One week later the group that had read it four times as often remembered 40 percent. The group that barely read it and kept testing remembered 61 percent.

Measured as forgetting rather than recall, the gap is starker. The heavy readers lost 52 percent of what they had known. The heavy testers lost 14 percent.

Why it is true

Reading again gives you the material. Recalling it makes you build the road back to the material. Those are two different jobs, and only one of them is the job you will actually need later.

Think about when you need the knowledge. In an exam, in a meeting, in a conversation with a doctor, nobody hands you the page. You have to produce the thing from nothing. Rereading practises recognising. Testing practises producing. You get better at the thing you practise, and recognising is the easier one, which is exactly why it feels better.

The psychologist Robert Bjork calls this family of methods desirable difficulties. Conditions that make learning slower and less pleasant now, and stronger later. Spacing your study out is another one. Mixing topics instead of doing one at a time is another.

The part that should worry you

Roediger and Karpicke also asked the students to predict, on a scale of one to seven, how well they thought they would remember the passage in a week.

The group that read four times and never tested rated itself 4.8. The two testing groups rated themselves 4.2 and 4.0.

So the group that performed worst was the group that was most confident. Rereading does not produce knowledge. It produces the feeling of knowledge, which is a different product, and your brain cannot tell them apart from the inside.

That is the surprising bit, and it is bigger than studying. You cannot trust the feeling of fluency anywhere. Watching a video of someone cooking, reading a business book, listening to a lecture, nodding through a training session. All of it feels like competence arriving and almost none of it is.

Where it is weak, honestly

These were short passages, read by American undergraduates, in a laboratory, over one week. That is not a full term of medical school and the authors say plainly that the limits of the effect are not yet mapped.

There is also a real condition attached. Testing works when you can already recall a decent share of the material. In these experiments the students recalled around 70 percent on the first test. If you try to retrieve something you have barely read, nothing comes back and you have wasted the hour. Self testing replaces the second reading, not the first one.

And it is one input among many. A tired child who did not sleep will not be rescued by better technique.

Where it shows up in your life

Money. You read an article about investing and feel informed. Close it and write, from memory, what you would actually do with 10,000 pounds and why. Most people cannot finish that paragraph, and finding that out is worth more than the article was.

Your children. Stop asking "did you understand?" A child will always say yes, and he believes it. Ask "close the book and tell me what it said." That single change turns study time into the method that works, and it costs nothing.

Your health. After a doctor explains a treatment, say it back in your own words before you leave the room. You will find the gap while you can still fix it, instead of at home at eleven at night.

The same rule applies to any long meeting at work. Before you open your notes, write the three things the other side actually wants. What you cannot produce from memory is what you did not really hear.

Three things to try

1. Tonight, ask your child to close the book and tell you the chapter. Not read it. Tell it. Then let him check what he missed.
2. Next time you finish a book or a long article, write five lines from memory before you look at anything. Do it again in a week.
3. Notice when learning feels comfortable, and treat that as a warning rather than a reward.