In one line: In a bidirectional relationship, two things each affect the other, round and round.
Think of stress and sleep. Stress makes it harder to sleep. Poor sleep then makes you more stressed the next day.
Each one feeds the other in a feedback loop. That is a bidirectional relationship.
The stress and sleep loop
Stress rises
A hard week leaves you tense.
Sleep gets worse
The tension makes it harder to fall asleep and to stay asleep.
Stress rises again
On little sleep, small problems feel bigger, and the loop goes round again.
Stress · Worse sleep · More stress
Remember: Not a line, a loop.
Bidirectional means the arrow points both ways.
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Key idea: When two things are found together, a study often cannot tell which one affects which.
A study finds that low mood and staying away from friends go together.
It is tempting to pick a direction. But low mood makes people withdraw, and withdrawing makes mood worse. Neither is simply "the cause".
Not being able to tell the direction from the data is called bidirectional ambiguity.
Reverse causation
- The arrow points the other way
- B leads to A, not A to B
- Still one direction
Bidirectional
- The arrow points both ways
- A leads to B and B leads to A
- A loop, not a line
How do researchers find out? They measure the same people more than once. If low mood in January comes before withdrawal in March, and withdrawal in March comes before lower mood in May, both directions are at work.
Exam tip: Do not stop at "we cannot tell the direction".
Say how each direction could work in the study you are given.
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Key idea: Behaviour rarely has one cause. Several things usually work together.
Two students both sleep badly before an exam. One does fine. The other, who is also very anxious, does poorly.
Lack of sleep did not decide the result alone. What it did depended on the other factor.
Influence
- One thing affects another
- Each factor adds its own share
- Poor sleep lowers scores a little
Interaction
- What one factor does depends on another
- Together they do more than each alone
- Poor sleep matters most for anxious students
Explaining a behaviour by one simple cause is called a reductionist explanation. It is easier to test, but it can leave out much of the story.
Watch out: "The cause of" is nearly always too strong.
Write "one cause of" or "a factor in", and say what else is involved.
How this is asked: Causality is one of the four concepts in the 15-mark question on a study you are given.
When a study links two things that could feed each other, show the loop.
The pattern
- Say that the study measured two things at one point in time.
- Explain the direction the researchers claim.
- Explain how the other direction could work.
- Say that both may be true: a loop.
- Add a second concept, then conclude.
The trap: "the direction is unclear" and nothing more: That is only the start.
Give a believable story for each direction, using the variables in the study.
Discuss the following study with reference to two or more of the following concepts: bias, causality, measurement and/or responsibility.
Researchers gave a questionnaire to 900 teenagers aged 13 to 16 in three schools. It asked how often they had been bullied online in the past year and included ten statements about self-esteem, each rated from 1 to 5. Teenagers who reported more online bullying had lower self-esteem scores. The researchers concluded that online bullying lowers self-esteem.
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