Spot graph-scale and base-rate limits in Psychology HL data

Psychology HL Paper 3 source booklet: The HL extension is motivation within human relationships. Source A graph reports task follow-through score for certificate reward focus (40) and community-purpose focus (54) from 132 participants using club sign-up and attendance records matched to message condition. Source B reports the qualitative theme "students described stronger commitment when tasks were linked to named community needs" from 14 participants using small focus groups after three meetings. Source C says attendance sheets show more completed tasks after purpose-focused planning. The claim is: "purpose-based motivation improves sustained service behaviour." Paper 3 Question 1 asks students to explain one issue that limits interpretation of the graph. Select the HL extension focus, source issue, data conclusion, and synthesis limit. Then answer this in your own words: what should the student write next to make this Psychology HL Paper 3 response stronger for the exact sources? AI will analyse your source interpretation, data reasoning, extension knowledge, research-method judgement, synthesis, and expression.