How to do psychological research

Null hypothesis (H₀)

A statement asserting no effect or relationship exists between variables.

Alternative hypothesis (H₁)

A statement suggesting an effect or relationship exists between variables.

Falsifiable

Capable of being proven false through evidence or experimentation.

One-tailed/directional hypothesis

Predicts the direction of the effect or relationship between variables.

Two-tailed/non-directional hypothesis

Predicts an effect or relationship without specifying its direction.

Scientific theory

A well-supported explanation of phenomena based on evidence and observation.

Qualitative

Non-numeric data focusing on descriptions, themes, or patterns.

Quantitative

Numeric data emphasizing measurement and statistical analysis.

Experimental design

A method for testing hypotheses by manipulating variables to observe outcomes.

Observational design

A method of studying behavior without direct intervention or manipulation.

Experiment vs. Study

An experiment manipulates variables to test causation, while a study may simply observe relationships.

Cause-and-effect relationship

A connection where one variable directly influences another.

Independent variable (IV)

The variable manipulated to assess its effect on the dependent variable.

Dependent variable (DV)

The variable measured to determine the effect of the independent variable.

Control variable

A variable held constant to prevent it from influencing results.

Variability

The extent to which data points differ from each other or the mean.

Counterbalancing

A method to control for order effects by varying the sequence of conditions.

Order effects

Changes in participants’ behavior due to the order of conditions.

Experimenter bias

Unintentional influence of the experimenter on results.

Participant bias

Participants’ behavior changes due to their awareness of being studied.

Hawthorne effect

Improved performance due to participants knowing they are observed.

Experimental group

The group exposed to the independent variable.

Control group

The group not exposed to the independent variable, serving as a baseline.

Placebo effect

A change in behavior due to participants’ expectations, not the treatment.

Single-blind

Participants are unaware of the condition they are in.

Double-blind

Both participants and researchers are unaware of the assigned conditions.

Confounds/extraneous variables

Variables other than the IV that may influence the DV.

Correlation

A statistical measure of the relationship between two variables.

Positive correlation

Both variables increase or decrease together.

Negative correlation

One variable increases as the other decreases.

Sample

A subset of individuals from the population being studied.

Population

The entire group of interest in a study.

Representative sample

A sample reflecting the characteristics of the population.

Random sampling

Selecting participants so each individual has an equal chance of inclusion.

Convenience/opportunity sampling

Selecting participants based on availability or accessibility.

Reliability

The consistency of a measurement or test.

Validity

The extent to which a test measures what it claims to measure.