An occupational psychologist conducted a correlational study to investigate whether there is a relationship between daily caffeine intake and self-rated workplace productivity. A sample of 12 office workers completed a self-report diary estimating their average daily caffeine consumption (in milligrams) and answered a work performance questionnaire (yielding a productivity score from 10 to 80, where higher scores represent higher perceived productivity).
| Participant | Daily Caffeine Intake (mg) | Workplace Productivity Score (10–80) | Rank: Daily Caffeine Intake | Rank: Workplace Productivity |
|---|---|---|---|---|
| P01 | 350 | 45 | 9.0 | 5.0 |
| P02 | 400 | 35 | 10.0 | 3.0 |
| P03 | 100 | 75 | 2.0 | 12.0 |
| P04 | 250 | 50 | 7.0 | 6.0 |
| P05 | 200 | 60 | 5.5 | 8.0 |
| P06 | 150 | 65 | 4.0 | 9.0 |
| P07 | 300 | 40 | 8.0 | 4.0 |
| P08 | 500 | 20 | 12.0 | 1.0 |
| P09 | 50 | 70 | 1.0 | 11.0 |
| P10 | 450 | 30 | 11.0 | 2.0 |
| P11 | 200 | 55 | 5.5 | 7.0 |
| P12 | 120 | 68 | 3.0 | 10.0 |
Outline two things that could have affected the validity of the data collected in this study.