Is the number meaningful?

Step 1 Warm-up recall

From M1.L2: how do you turn WHO-5 ratings into a 0 to 100 score? Write the rule in one line.

The rule

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Step 2 Learning goal

By the end of this lesson you can:

• define reliability and validity, and give one way to check each (Foundation);
• name four threats to self-reported well-being and one safeguard for each (Core);
• judge whether a stated claim is justified by the measure behind it (Core).

Step 3 A familiar example

A bathroom scale reads 2 kg too heavy every morning. It is perfectly consistent, and it is wrong. A second scale gives readings that jump around but average the true weight. The first is reliable and not valid. The second is closer to valid and not reliable. Scores on a well-being scale can fail in either way.

Step 4 Clear explanation

Reliability is consistency. Internal consistency asks whether the items of a scale agree with one another, often summarised by Cronbach’s alpha. Test-retest reliability asks whether the same person gets a similar score twice, a short time apart. A value of 0.70 or above is often treated as acceptable for alpha. That is a convention, not a law.

Validity is whether the scale measures what it claims to. Convergent validity: scores relate to measures of related ideas, and to how other people who know the person rate them. Discriminant validity: they do not simply repeat unrelated ideas. Reviews of life-satisfaction measures generally find moderate, not perfect, agreement with other people’s ratings.

Reliability is necessary but not sufficient for validity. A scale can be consistent and still miss the idea.

Four threats to self-report:

Step 5 Worked example (4 marks)

A company surveys all staff on the last Friday before the year-end break, using one unnamed question, “Are you happy?”, and reports “90% of staff are happy”. Name four problems and one fix for each.

1. Timing: the mood of the day inflates answers. Fix: ask at several ordinary times. (1 mark)
2. One unvalidated item: nothing shows it is reliable or valid. Fix: use a published scale such as the SWLS. (1 mark)
3. Unclear account: “happy” could mean feeling or judgement. Fix: state which account the question asks about. (1 mark)
4. Social desirability if answers are not anonymous. Fix: anonymous responses. (1 mark)

Step 6 Learner practice (instant-marked)

Step 7 Recap

• Reliability is consistency. Validity is measuring the intended idea.
• Reliability is necessary but not sufficient for validity.
• Four threats: context, social desirability, uneven scale use, question order.
• Each threat has a safeguard. None removes it entirely.

Step 8 Exit ticket (ungraded)

Think of a well-being survey you have answered. Which threat was most likely to affect your answers?

Your answer

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Step 9 Go further (Extension)

Look up the four personal well-being questions asked in UK Office for National Statistics surveys (life satisfaction, worthwhile, happy yesterday, anxious yesterday). For each, say which of the three accounts from M1.L1 it mainly speaks to, and name one threat from this lesson that could affect the answers.