Because many psychological constructs (like "happiness" or "intelligence") cannot be observed directly, researchers must create an operational definition. This is a specific, measurable description of how a variable will be quantified in a particular study. For example, "aggression" might be operationally defined as "the number of times a participant hits a punching bag in five minutes."
Achieving high-quality results requires balancing three types of validity:
- Construct Validity: Does the test actually measure the concept it claims to measure?
- Internal Validity: Can we confidently say that the change in the dependent variable was caused by the independent variable, rather than an outside factor?
- External Validity: Can the results be generalized to other people, settings, or times?
Research Designs and Methodologies
Researchers choose their design based on their ability to control the environment and the nature of their research question.
Nonexperimental and Correlational Designs
When researchers want to see if two variables are related without manipulating them, they use correlational designs. A correlation can be positive (both variables increase together), negative (one increases while the other decreases), zero (no relationship), or curvilinear (the relationship changes direction, like an inverted U).
Note: Correlation does not equal causation!
Experimental and Quasi-experimental Methods
The experimental method is the gold standard for determining causation. In a true experiment, researchers use random assignment to place participants into groups, ensuring that any differences between groups are due to the manipulation of the independent variable (the cause) rather than pre-existing differences. The effect is then measured on the dependent variable.
When random assignment is impossible—such as when studying a pre-existing group like "smokers" or conducting research in a natural setting—researchers use quasi-experimental designs.
Survey Research
Survey research is a common way to collect data from large groups via mail, the internet, or interviews. Researchers use open-ended questions (allowing for free response) or close-ended questions (providing fixed options). A common tool in surveys is the Likert scale, which asks participants to rate their level of agreement (e.g., from "Strongly Disagree" to "Strongly Agree").
Sampling: Who is in the Study?
To ensure results are representative of a larger population, researchers must use careful sampling techniques.
- Probability Sampling: Every member of the population has a known, non-zero chance of being selected. This includes simple random sampling, stratified sampling (ensuring subgroups are represented), and cluster sampling. These methods allow for much better generalization.
- Nonprobability Sampling: Selection is not random, which can lead to bias. Examples include haphazard sampling, quota sampling, and snowball sampling (where participants recruit other participants).
Ethics in Research
Ethical guidelines are not just suggestions; they are strictly enforced to prevent the historical abuses seen in studies like the Tuskegee Syphilis Study. Modern ethics are guided by the Nuremberg Code and the Belmont Report, and overseen by an Institutional Review Board (IRB).
Researchers must follow APA guidelines, which emphasize principles such as beneficence/nonmaleficence (doing good and avoiding harm), integrity, justice, and respect for people's rights and dignity.
Key Ethical Requirements
- Informed Consent: Participants must be told enough about the study to decide whether they want to participate.
- Deception: Sometimes, researchers must use deception (omission or commission) to prevent participants from changing their behavior. If deception is used, researchers must conduct a debriefing immediately after the study to explain the true purpose.
- Confidentiality: Protecting the privacy of participants' data is paramount.
- Cost-Benefit Analysis: Researchers must ensure that the potential scientific benefits of a study outweigh any physical or psychological risks to participants.
