Direction of cause in relationship research

Step 1 Warm-up recall

From M2.L4: name the three routes by which an association can arise other than “A causes B”.

Your answer

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Step 2 Learning goal

By the end of this lesson you can:

• describe reverse causation and a third factor in relationship research (Foundation);
• say what evidence would support each route (Core);
• write a careful sentence about social ties and health (Core).

Step 3 A familiar example

Someone who is ill may go out less, so fewer ties could follow poor health. But someone with few ties may also look after their health less. Both can be true.

Step 4 Clear explanation

Large reviews such as the two in this module pool observational studies. In such data, the same association can arise three ways:

• Ties influence health (for example through support, or through encouragement to look after oneself).
• Health influences ties (reverse causation): illness or low mood can reduce contact.
• A third factor, such as income or neighbourhood, affects both.

Whether a study adjusted for people’s initial health is worth checking in the original paper: doing so speaks to the second route but does not remove it. Evidence that would strengthen a causal reading includes tracking people over time, measuring ties before illness appears, and trials that change ties. The 2015 review controlled for confounds, which is the third route; controls are only as good as the factors measured.

A careful sentence: “Across many studies, stronger social ties were associated with higher odds of survival; the studies cannot by themselves show how much of that is due to the ties.”

Step 5 Worked example (4 marks)

A headline says “Making friends adds years to your life”.

1. The underlying evidence is a pattern across observational studies. (1 mark)
2. Reverse causation: poor health may reduce contact. (1 mark)
3. A third factor may affect both ties and survival. (1 mark)
4. Fair claim: stronger ties are associated with better survival; causal size is uncertain. (1 mark)

Step 6 Learner practice (instant-marked)

Step 7 Recap

• The same association can arise through effect of ties, reverse causation or a third factor.
• Controls reduce but do not remove these routes.
• Trials that change ties give the strongest causal test.

Step 8 Exit ticket (ungraded)

Write one careful sentence about social ties and health suitable for a newspaper.

Your answer

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Step 9 Go further (Extension)

Look for a trial of a social-connection programme that followed health outcomes. Note its design and size.