| Social | Self-reporting data, questionnaires and interviews |
| Cognitive | Field and lab experiments, case studies of brain damaged patients |
| Biological | Correlations, brain scanning, twin and adoption studies |
| Learning | Observations, content analysis, animal experiments |
| Clinical | Longitudinal, cross-sectional, cross-cultural, meta-analyses, case studies, interviews |
| Child | Observations, questionnaires and interviews, cross-cultural |
Lab experiment: Milgram, Burger, Baddeley, Sebastian and Hernandez Gil
Case experiment: Watson and Rayner
Field study: Rosenhan
Animal lab experiment: Pavlov, Skinner
Review of secondary data: Carlsson et al
Structured/controlled observation: Ainsworth, Bandura et al
Interview: Vallentine et al
Interview/self-report: Capafons et al
Questionnaire/self-report: Williams et al
Twin study: Gottesman and Shields, Brengden et al
Adoption study: Heston
Longitudinal study: Li et al
Meta-analysis: van Ijzendoorn and Kroonenberg
PET scan: Raine et al
Case study: Lavarenne et al, Genie, Czech twins