How to Remember What You Studied Last Month

Knowing something in the hour after you studied it and knowing it four weeks later are two different things, and the first is a poor guide to the second. This post covers what helps knowledge last, with a plan for the month after you first study a topic.

How to tell whether you will remember it

Psychologists distinguish performance, which is what you can do right now, from learning, the lasting change that can only be measured later. A review by Nicholas Soderstrom and Robert Bjork describes how performance while you study is often an unreliable guide to learning.

Answering correctly straight after studying something is mostly performance. The answer is still at the front of your mind, the wording of the question matches what you just read, and you are in the same place. Those cues will not be there in the exam.

So judge a study block by what you can write down two days later without notes, rather than by how confident you feel at the end of it. The check takes about five minutes.

Come back after a delay

A correct answer after a few days tells you more than one after a few minutes, and it does more for the memory. In experiments by Karpicke and Roediger, delaying the first test so that recall took more effort improved retention on a later test.

How long the delays should be is covered in the forgetting curve. Knowing something while the notes are open is not much evidence that you will know it without them.

Connect facts to the reasons behind them

A fact with one route into it can disappear when that route fails. A fact tied to a reason has more than one, and can often be rebuilt when direct recall fails.

Take the pharmacology rule of thumb that a drug is almost entirely cleared after four to five half-lives. As a bare number, it is easy to forget or mix up. With the reason attached, you can rebuild it. Most drugs are eliminated at a rate proportional to how much is in the body, so each half-life removes half of what is left (StatPearls). After one half-life 50% remains, then 25%, then 12.5%, about 6% after four and about 3% after five.

Three habits help:

• Ask why a fact is true, and follow the answer one step further than feels necessary.
• Compare each idea with the one it is most easily confused with, such as sensitivity and specificity in statistics, and write the difference in one sentence.
• Look for the same principle elsewhere in your courses. Equilibrium, for example, turns up in chemistry, economics and physiology.

Keep a list of your mistakes

Reading the right answer once does not always fix a mistake. In a study by Andrew Butler, Lisa Fazio and Elizabeth Marsh, people answered science questions, were shown the correct answers, and were tested again a week later. When they had forgotten a correction, they sometimes gave the same wrong answer again, and errors they had been confident about were the most likely to come back.

So keep a record and work through it on a delay:

1. Write down the question, your answer, the correct answer, and the page or slide where the correct version is taught.
2. A few days later, cover the correct answer and try to produce it from memory.
3. Keep the mistake on the list until you have got it right on more than one later day.

SymbioLearn keeps this list for you as Mistakes. Each wrong quiz answer is kept under its Concept, beside the right answer and the Source line it came from, and Revisit Mistakes quizzes you on just those points.

Note where each idea came from

A month later, you may remember that a diagram or a worked example explained something, but not what it said. If your notes record where each point came from, finding it again takes a minute. If they do not, it can mean searching a 300-page PDF or scrubbing through a 50-minute video.

So add page numbers, slide numbers or timestamps as you take notes.

Practise in different ways

If you always practise with the same question in the same wording, you may come to depend on that wording. Elizabeth and Robert Bjork list varying the conditions of practice among the difficulties that often improve learning. Practising recall also helps with new questions: in experiments by Andrew Butler, students who had repeatedly tested themselves on passages did better a week later on new questions that asked them to draw inferences from what they had read.

Vary how you come back to a topic:

• Explain it aloud as if to someone in the year below.
• Answer a question worded differently from the ones you wrote.
• Work a problem that uses the idea.
• Draw the diagram or process from memory.

Protect your sleep

Memory keeps being consolidated after you stop studying, and sleep helps. A review by Susanne Diekelmann and Jan Born describes sleep as helping to consolidate newly learned information, depending on what was learned and when the sleep comes. Losing sleep before you study hurts too: in one study, a single night without sleep left people worse at forming new memories the next day.

In practice, do not routinely swap sleep for extra revision hours. There is more on this in what sleep does for studying.

A one-month plan

1. Day 1: learn the topic properly, then close your notes and write down what you can.
2. Day 3 or 4: write it out again from memory, then check.
3. About a week later: explain it aloud without notes.
4. About three weeks later: answer a question you have not seen before, or work a problem that uses the idea.

At every step, anything you get wrong goes on your mistakes list and comes back sooner. Anything you get right easily twice can wait longer.

For example, take price elasticity of demand in economics. On day 1, write the definition and the formula: the percentage change in quantity demanded divided by the percentage change in price. On day 4, add what makes demand more elastic, such as close substitutes. A week later, explain aloud why raising the price of a product with elastic demand lowers revenue. Three weeks later, try a new question: if a 10% rise in bus fares cuts journeys by 4%, what happens to the bus company's revenue? It rises, by about 5.6%, because demand is inelastic (1.10 × 0.96 = 1.056).

What to do today

1. Pick a topic you studied about four weeks ago.
2. Without opening anything, write down what you remember.
3. Check it against your notes, and put what you missed on your mistakes list.
4. Plan your next attempt for a few days from now.

If you would rather have that history kept for you, Concept by Concept across a course, that is what a Module in SymbioLearn does.