Define and frame
Calculate the three within-person post-minus-pre differences and their mean.
Scenario: Suppose three people have pre/post scores of 60/63, 70/76 and 80/82. These are not independent groups.
Use the fictional dataset if the question refers to it. Always show your reasoning; an exact number without context is not enough. The four written tasks are teacher-assessed. The self-check below is formative and does not affect the 20-mark assignment.
Written problem set
Calculate or apply
Explain why a paired t-test is appropriate and how it differs from a two-independent-group comparison.
Evaluate the design
Explain why Welch's test is useful when comparing independent A and B groups with potentially unequal variances.
Interpret and communicate
Give two reasons a pre/post increase does not prove the method caused improvement.
Standard scoring guide
Each written task is worth 5 points: correct key idea (2), justified application or computation (2), and a clear statement with limits (1). This original rubric is not official UCL assessment.
Formative self-check · 4 questions
Choose one answer for each item, then check the feedback. Answers and explanations are available on this public study page; the separate written-task instructor key is private.