AP Psychology: Research Methods & Statistics — Comprehensive Notes

Scientific Thinking & Theory Building

• Critical thinking: the process of actively and skillfully analyzing, evaluating, and synthesizing information to reach an answer or conclusion that can be justified
• Hindsight bias: the tendency to believe, after learning an outcome, that one would have foreseen it (the "I-knew-it-all-along" phenomenon)
• Theory: an explanation using an integrated set of principles that organizes observations and predicts behaviors or events
• Hypothesis: a testable prediction, often implied by a theory
• Peer reviewers: scientific experts who evaluate research manuscripts before publication to ensure quality, accuracy, and significance

Research Methods

• Descriptive Research Methods
  • Case study: an observation technique in which one person is studied in depth in the hope of revealing universal principles
  • Naturalistic observation: observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation
  • Survey: a technique for ascertaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sample of the group
• Experimental Research
  • Experiment: a research method in which an investigator manipulates one or more factors (independent variables) to observe the effect on some behavior or mental process (the dependent variable)
  • Experimental group: the group exposed to the treatment, that is, to one version of the independent variable
  • Control group: the group not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment
• Random assignment
  • Random assignment: assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups
• Code: pAsGwQ

Variables & Controls

• Variable: any factor that can vary in amount or type
• Independent variable: in an experiment, the factor that is manipulated; the variable whose effect is being studied
• Dependent variable: in an experiment, the outcome that is measured; the variable that may change when the independent variable is manipulated
• Confounding variable: in an experiment, a factor other than the factor being studied that might influence a study's results
• Operational definition: a carefully worded statement of the exact procedures (operations) used in a research study

Research Quality & Controls

• Replication: repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding can be reproduced
• Validity: the extent to which a test or experiment measures or predicts what it is supposed to
• Single-blind procedure: an experimental procedure in which research participants are ignorant (blind) about whether they have received the treatment or a placebo
• Double-blind procedure: an experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo
• Placebo effect: experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent
• Experimenter bias: the unconscious tendency for researchers to treat members of the experimental and control groups differently to increase the chance of confirming their hypothesis

Sampling & Population

• Population: all those in a group being studied, from which samples may be drawn
• Random sample: a sample that fairly represents a population because each member has an equal chance of inclusion
• Sampling bias: a flawed sampling process that produces an unrepresentative sample
• Social desirability bias: the tendency of survey respondents to answer questions in a manner that will be viewed favorably by others
• Self-report bias: the tendency for people to inaccurately report their own behaviors, attitudes, or other personal characteristics

Correlational Research

• Correlation: a measure of the extent to which two factors vary together, and thus of how well either factor predicts the other
• Correlation coefficient: a statistical index of the relationship between two things (from -1.00 to +1.00)
• Scatterplot: a graphed cluster of dots, each of which represents the values of two variables
• Illusory correlation: perceiving a relationship where none exists, or perceiving a stronger-than-actual relationship
• Regression toward the mean: the tendency for extreme or unusual scores or events to fall back (regress) toward the average
• Correlation coefficient range: $-1 \, \le\, r \, \le\, 1$

Descriptive Statistics

• Descriptive statistics: numerical data used to measure and describe characteristics of groups
• Mean: the arithmetic average of a distribution
  • $\text{Mean} = \frac{\sum<em>{i=1}^n x</em>i}{n}$
• Median: the middle score in a distribution; half the scores are above it and half are below
  • For odd n: the middle value after ordering
  • For even n: the average of the two middle values: $\text{Median} = \begin{cases} x<em>{\frac{n+1}{2}} & n \text{ odd} \ \frac{x</em>{\frac{n}{2}} + x_{\frac{n}{2}+1}}{2} &amp; n \text{ even} \end{cases}$
• Mode: the most frequently occurring score(s) in a distribution
• Range: difference between the highest and lowest scores
  • $\text{Range} = x<em>{\max} - x</em>{\min}$
• Standard deviation: a measure of how much scores vary around the mean (sample)
  • $\text{SD} = \sqrt{\frac{1}{n-1}\sum<em>{i=1}^n (x</em>i - \bar{x})^2}$
• Histogram: a bar graph depicting a frequency distribution
• Percentile rank: the percentage of scores in a distribution that a specific score is greater than or equal to
• Skewed distribution: scores lacking symmetry around their average value
• Normal curve: a symmetrical, bell-shaped curve describing the distribution of many data types; most scores near the mean, fewer near the extremes

Inferential Statistics & Analysis

• Inferential statistics: numerical data that allow one to generalize—inferring from sample data the probability of something being true of a population
• Statistical significance: a statistical statement of how likely it is that an obtained result occurred by chance
• Effect size: a measure of the strength of the relationship between two variables

Meta-analysis

• Meta-analysis: a statistical procedure for analyzing the results of multiple studies to reach an overall conclusion

Research Ethics & Types

• Quantitative research: research that relies on numerical measurement and statistical analysis
• Qualitative research: research that focuses on qualities and characteristics that cannot be measured numerically
• Informed consent: giving potential participants enough information about a study to enable them to choose whether they wish to participate
• Debriefing: the postexperimental explanation of a study, including its purpose and any deceptions, to its participants

Notes on Theory, Practice, and Context

• The integration of descriptive, correlational, and experimental methods is used to build and test scientific theories
• Ethical considerations include ensuring voluntary participation, minimizing harm, and providing transparency about deception and its necessity
• Real-world relevance: findings inform education, clinical practice, policy, and everyday decision-making
• Limitations and trade-offs: descriptive methods provide depth or breadth but may lack generalizability; experimental methods offer control but may reduce ecological validity
• Relationship to foundational principles: measurement validity, reliability, and the scientific method underpin all analyses and inferences

Quick reference of key terms (glossary)

• Critical thinking, hindsight bias, theory, hypothesis, peer review, descriptive/descriptive statistics, replication, validity, single/double-blind, placebo effect, experimenter bias, population, sample, sampling bias, social desirability bias, self-report bias, correlation, correlation coefficient, scatterplot, illusory correlation, regression toward the mean, mean, median, mode, range, standard deviation, histogram, percentile rank, skewed distribution, normal curve, inferential statistics, statistical significance, effect size, meta-analysis, quantitative vs qualitative research, informed consent, debriefing