In one line: In a bidirectional relationship, each variable is both a cause and an effect of the other.
Some children are often aggressive, and some are rejected by their classmates. The two go together.
Classmates avoid a child who hits out. Being left out then makes that child angrier and more likely to hit out again. Each variable drives the other: a bidirectional relationship, kept going by a feedback loop.
The aggression and rejection loop
A child is aggressive
He pushes and shouts when a game does not go his way.
Classmates reject him
They stop choosing him, so he has fewer chances to practise getting on with others.
He becomes more aggressive
Feeling left out and having fewer skills, he hits out more, and the loop continues.
Aggression · Rejection · More aggression
Remember: In a loop, asking "which is the cause?" has no single answer.
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Key idea: A correlation is silent about direction. Either variable could come first, or both.
When a study cannot tell which of two related variables affects the other, this is bidirectional ambiguity. It is a limit of the design, not a finding about the world.
Bidirectional ambiguity
- We cannot tell the direction
- A weakness of a one-off correlation
- Removed by a better design
A bidirectional relationship
- Both directions are real
- A feature of the behaviour itself
- Shown by evidence for each direction
To move from the first to the second, researchers follow the same people over time. If aggression at age six predicts rejection at seven, and rejection at seven predicts more aggression at eight, both directions have evidence.
An experiment can also test one direction at a time, where that is ethical.
Exam tip: Keep the two phrases apart.
"The study has bidirectional ambiguity" is a criticism. "The relationship may be bidirectional" is an explanation.
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Key idea: Human behaviour is complex. A cause usually works through, and together with, other variables.
Not every child who is rejected becomes more aggressive. Whether that happens depends on the child's temperament, on how parents respond, and on whether there is one good friend.
Influence
- A variable has its own effect
- Effects simply add up
- Rejection raises aggression somewhat
Interaction
- The effect of one variable depends on another
- Together they differ from the sum
- Rejection raises aggression mainly in children with a quick temper
An account that reduces a behaviour to one simple cause is reductionist. It is easier to test, which is its strength, and it leaves out interactions, which is its weakness.
People also have agency: they choose friends, places and habits. That is one reason arrows so often run both ways.
Watch out: Complexity is not an excuse to say nothing.
Name the other variables, and say how they would change the effect.
How this is asked: In the 15-mark question on an unseen study, causality is one of the four concepts offered.
A one-off survey that links a behaviour with a state of mind is where direction matters most.
The pattern
- Identify the design and the direction the researchers claim.
- Give the mechanism for the opposite direction.
- Argue that the relationship may be bidirectional, and what would show it.
- Add other variables that the effect could depend on.
- Apply a second concept, then judge the conclusion and any recommendation.
The trap: two separate lists: A paragraph on causality and a paragraph on bias, side by side, is not yet a discussion.
Show how one concept changes what can be said about the other.
Discuss the following study with reference to two or more of the following concepts: bias, causality, measurement and/or responsibility.
Researchers surveyed 600 adults aged 40 to 60. Each adult reported how many minutes of exercise they take in a typical week and completed a questionnaire that screens for symptoms of depression. Adults who exercised less had more symptoms of depression. The researchers concluded that a lack of exercise causes depression and recommended that doctors prescribe exercise.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.