Internal validity - the theories of the scientific approach to Psychology are based on the findings of psychological experiments that are easily influenced by demand characteristics and investigator effects, so have low internal validity.
Disadvantage because - we can't know whether the change to the dependent variable (DV) was due to manipulation of the independent variable (IV) or other extraneous variables.
- Buss's questionnaire about human mate preferences asked participants personal questions about their ideal life partner, and to rate characteristics like chastity.
- Their answers may have been affected by social desirability bias, making the findings invalid.
External validity - an experimental situation is artificial and can be unlike the real-life situations that are being investigated, so has low external validity.
Disadvantage because - using a scientific approach to controlling an experiment can make the results impossible to generalise to the real-life setting, due to the artificiality created by the control of extraneous variables.
- Mandel points out that Milgram intended to use his findings to understand atrocities in Nazi death camps, but his experimental set-up had little similarity to this (or any other) real-life setting.
- One of the differences between his experiment and Nazi atrocities is that Milgram told his participants that the victim had agreed to take part, and the shocks would cause no lasting damage.
Reductionism - the scientific method requires terms to be reduced by operationalising them to make them measurable. (N.B. This is the case for non-experimental methods too - behavioural categories are produced for observations.)
Disadvantage because - it can over-simplify the complexity of human emotion and behaviour.
- Selye's research into the biological response to stress ignored the psychological response by reducing stress to biological symptoms.
- He also oversimplified the complex psychological processes of humans by generalising his findings from rats to humans.
Individual differences - science takes a nomothetic approach - making generalisations about people and ignoring the differences between individuals.
Disadvantage because - differences between genders, cultures, ages, and other individual differences (including species) are overlooked, when they may be important.
- Most research is carried out on American college students.
- Generalising these findings to the rest of the population disregards the possibility that factors like intelligence, educational background and socio-economic status are relevant variables.
Ethical issues - ethical issues such as informed consent, deception and protection of participants are often raised in psychological research. The key consideration is whether the benefits outweigh the ethical costs.
Disadvantage because - even if the costs are justified, the participants may have been harmed in some way.
- Important knowledge was gained from Milgram's study.
- This does not change the fact that participants were frequently distressed by the procedure and may have suffered some psychological harm.