Behavioral Genetics and Psychological Research Methods

Behavioral Genetics and the Biology of Personality

• Behavioral Genetics Definition:

  • Behavioral genetics is the field of study devoted to determining just how much of an individual's personality is due to inherited traits.

• Foundations in Animal Breeding:

  • Animal breeders have long demonstrated that selective breeding of animals with specific desirable traits yields changes not only in physical characteristics (such as size and fur color) but also in the temperament of the animals (Isabel, 2003; Trut, 1999).

  • Temperament: Consists of the characteristics with which each person is born and is, therefore, determined by biology to a great degree.

  • Inference to Human Personality: If animal temperaments can be modified by manipulating patterns of genetic inheritance, personality characteristics related to temperament in human beings are likewise influenced by heredity.

  • Methodological Contrast: Animal breeders can control mating pairs and environmental raising conditions. Human research cannot ethically or practically exert such control, relying instead on accidental "experiments" of nature and opportunity (studies of twins and adopted individuals).

Twin Studies in Personality Research

• Genetic Sharing Baselines:

  • Monozygotic (Identical) Twins: Originate from a single fertilized egg and share $100\%$ of their genetic material.

  • Dizygotic (Fraternal) Twins: Originate from two separate eggs and share approximately $50\%$ of their genetic material, identical to any standard pair of biological siblings.

• Methodological Logic:

  • Comparing identical twins to fraternal twins—especially twins separated shortly after birth and raised in different environments—isolates genetic influences on personality traits from environmental influences.

• Case Example: The "Jim" Twins:

  • James Arthur Springer and James Edward Lewis (known as the "Jim" twins) were separated shortly after birth and reunited at age $39$. Despite being raised apart, they exhibited extensive similarities in personality, personal habits, and behavioral tendencies.

• Findings from the Minnesota Twin Study:

  • Identical twins are significantly more similar than fraternal twins or unrelated individuals across several traits, even when raised in completely separate environments:

    • Intelligence

    • Leadership abilities

    • Tendency to follow rules

    • Tendency to uphold traditional cultural expectations (Bouchard, 1997; Finkel & McGue, 1997)

    • Nurturance (defined as affectionate care and attention) (Neale et al., 1986)

    • Empathy (defined as the ability to understand the feelings of others) (Neale et al., 1986)

    • Assertiveness (Neale et al., 1986)

    • Aggressiveness (Miles & Carey, 1997)

Adoption Studies and Environmental Influences

• Methodological Logic:

  • Where twin studies evaluate genetically identical individuals raised in different environments, adoption studies evaluate genetically unrelated individuals raised in the same home environment.

  • Comparing adopted children to their adoptive parents/siblings as well as their biological parents isolates shared and nonshared environmental influences from genetic influences.

• Core Findings:

  • Adoption studies confirm twin study data: genetic influences account for a significant portion of personality development regardless of shared or nonshared environments (Hershberger et al., 1995; Loehlin et al., 1985; Loehlin et al., 1998).

  • A clear genetic basis has been demonstrated for specific traits including:

    • Shyness (Plomin et al., 1988)

    • Aggressiveness (Brennan et al., 1997)

Heritability and Current Genetic Findings

• Concept of Heritability:

  • Heritability Definition: The degree to which a specific trait within a population can be attributed to genetic influences, and the extent to which individual genetic variation impacts differences in observed behavior.

  • Population Focus: Heritability measures variations across a population as a whole (e.g., intelligence on the East Coast of America, height in Eastern Asia) rather than individual trait percentages.

• Heritability Rates of the Big Five Personality Traits:

  • The five factors of the Five-Factor Model demonstrate nearly a $50\%$ rate of heritability across multiple cultures (Bouchard, 1994; Herbst et al., 2000; Jang et al., 1996; Loehlin, 1992; Loehlin et al., 1998).

  • In a study of $696$ twin pairs by Kandler et al. (2010):

    • Monozygotic twins exhibited a correlation of approximately $45\%$ ($0.45$) for self-ratings across each of the Big Five domains (Neuroticism, Extraversion, Openness, Agreeableness, Conscientiousness).

    • Dizygotic twins exhibited a correlation of approximately $22\%$ ($0.22$) across the same domains.

• Overall Personality Variance Estimates:

  • Variations in personality traits are estimated to be $25\%$ to $50\%$ inherited (Jang et al., 1998).

  • Environmental influences account for the remaining approximate $50\%$ of variation in personality traits.

  • Genetic techniques are actively used to investigate the relationship between personality and psychopathology (Plomin & Spinath, 2004).

Basic Concepts of Research in Psychology

• Scientific Method Definition:

  • Scientific Method: A method of studying nature based on systematic observation, strict rules of evidence, and critical thinking.

  • Core Critical Questions:

    • What is the evidence?

    • How good is the evidence?

    • What are the alternative explanations for the evidence?

    • What needs to be learned next?

• Empirical Evidence and Inferences:

  • Empirical Evidence: Evidence based on observations of publicly observable phenomena (such as behavior) that can be confirmed by other observers.

  • Psychological Application: Publicly observable behavior is recorded to draw inferences about private mental processes that cannot be directly observed.

• Operational Definitions:

  • Operational Definition: A definition used in science explicitly based on the procedures or operations used to measure a scientific phenomenon, including behavior.

  • Comparative Example (Bus Driver Daydreaming Study):

    • Non-Operational Statement (Statement A): "Sixty percent ($60\%$) of Chicago bus drivers daydream while driving their buses."

    • Operational Statement (Statement B): "Sixty percent ($60\%$) of Chicago bus drivers answered 'yes' to the question 'Do you ever daydream when driving your bus?'"

  • Evaluation Value: Knowing the operation of measurement allows critical evaluation of potential biases (e.g., memory accuracy, honesty on sensitive subjects, confidentiality trust, embarrassment).

• Theories and Hypotheses:

  • Theories: Tentative explanations of facts and relationships in sciences. Scientific theories are never absolute "truths" and are continuously revised or abandoned based on empirical testing.

  • Hypothesis: A specific prediction based on a theory that is tested in an empirical study.

  • Delinquency Theory Application (Terrie Moffitt, 1993):

    • Theory posits that youth becoming juvenile delinquents prior to puberty differ fundamentally from those who commit crimes only post-puberty.

    • Tested Hypothesis (Lahey & others, 1998): Juvenile delinquents committing crimes during childhood are more violent than other juvenile delinquents (hypothesis confirmed).

• Replication:

  • Replication Definition: Repeating studies based on the scientific principle that the results of studies should be doubted until the same results have been found in similar studies by other researchers.

• Representativeness of Samples:

  • Sample: A group of human or nonhuman research participants studied to learn about an entire population.

  • Representative Requirement: Findings are valid only if the sample accurately represents the target population.

  • Biased Sample Example: Testing work-marriage happiness correlation using clients from a marital therapy clinic yields a biased sample because clinic clients seeking help are not representative of all married persons.

Descriptive Research Methods

• Descriptive Studies Definition:

  • Descriptive Studies: Methods of observation used to describe predictable behavior and mental processes as people live their lives.

• The Survey Method:

  • Survey Method Definition: A research method that uses interviews and questionnaires with individuals to gather self-reported data on opinions, beliefs, or behaviors (Zimbardo, 2004).

  • NIMH Seasonal Mood Study (Kasper & others, 1989):

    • Random telephone survey of $416$ adults living in Maryland and Virginia asking for the month in which they felt worst over the preceding year.

    • Findings: Worst feelings peaked in winter months (January and February), correlating directly with the lowest temperatures and shortest daylight minutes.

    • Replication: Replicated across multiple studies (Agumadu & others, 2004), though Keller & others (2005) identified summer mood dips during hot, muggy weather.

*   **Methodological Limitations of Surveys:**

    1.  *Unrepresentative Samples:* Non-random sampling creates selection bias (e.g., surveying visitors on a conservative political website regarding tax breaks for the wealthy).

    2.  *Self-Report Dishonesty:* Participants may withhold honest responses on sensitive topics such as sex and drug use.

    3.  *Administration Effects:* Outcomes vary based on interviewer demographics (e.g., higher endorsement of feminist views when interviewed by women; Huddy & others, 1997) and subtle question wording changes (Schwarz, 1999; Waenke, Schwarz, & Noelle-Neumann, 1995).

• Naturalistic Observation:

  • Naturalistic Observation Definition: Research method based on recording behavior as it occurs in natural life settings without experimental manipulation.

  • Field Applications:

    • Jane Goodall: Field research on wild ape troops in Africa revealed ape social structures, intentional ambushes, and deadly attacks against other apes.

    *   *Irenaus Eibl-Eibesfeldt (1968):* Cross-cultural greeting observation identified universal human behaviors: smiling, head nodding, and brief eyebrow raising.

    *   *Other Applications:* Child play/friendship patterns, corporate leadership tactics, peer dynamic influence in juvenile delinquency.

• The Clinical Method:

  • Clinical Method Definition: Method of studying people while they are receiving psychological help from a mental health professional.

  • Historical Context: Sigmund Freud constructed theories of abnormal behavior by identifying consistent patterns in patient behavior, thoughts, and emotional expressions during therapy sessions.

  • Modern Application: Used for preliminary evaluations of treatment protocols (e.g., tracking daily anxiety measurements before, during, and after therapy).

Correlational Research Studies

• Correlational Method Definition:

  • Correlational Method: A research method that measures the strength and direction of the statistical relationship between quantitative variables.

  • Variable: Any factor that can be assigned a numerical value.

  • Quantitative Measures: Units of measure expressed in explicit numerical terms (e.g., hours of violent television watched per week; count of aggressive acts committed per week).

• The Correlation Coefficient:

  • Correlation Coefficient Definition: The numerical expression of the strength and direction of a relationship between two quantitative variables, ranging from $-1.00$ through $0.00$ to $+1.00$.

  • Positive Correlation ($+1.00$): As scores on one variable increase, scores on the second variable increase proportionally. Lower scores on one variable predict lower scores on the other.

*   **Negative Correlation ($-1.00$):** As scores on one variable increase, scores on the second variable decrease proportionally. Higher scores on one variable predict lower scores on the other.

*   **Comparative Strength:** A coefficient of $-1.00$ and a coefficient of $+1.00$ represent equal predictive strength; they differ only in direction.

*   **Zero Correlation ($0.00$):** Indicates no statistical relationship between variables. Knowing a score on one variable provides zero ability to predict a score on the second variable.

*   **Realistic Correlations ($-\!0.68$):** Represents a strong correlation in actual psychological research where individual data points scatter near a central trendline.

• Media Violence Correlational Data:

  • Over $200$ published psychological studies analyze exposure to media violence (Anderson & others, 2001; Huesmann, Moise, & Podolski, 1997; Konijn & others, 2007).

  • Observed correlations between watching media violence and real-life violent behavior range between $+.20$ and $+.30$ (Anderson & Bushman, 2001; Anderson & others, 2003; Paik & Comstock, 1994).

  • Societal Impact: A small correlation of $+.20$ to $+.30$ implies that $8$ out of every $100$ children viewing media violence are influenced toward aggressive behavior.

• Causation Limitation:

  • Correlation does not mean causation. Correlational studies cannot identify cause and effect due to:

    1. Reverse Causality: Aggressive youth may actively choose to consume more violent media.

    2. Third-Variable Problem: Unmeasured external factors (e.g., lack of parental supervision) may independently cause both high violent media consumption and high real-life aggression.

Formal Experiments and Cause-and-Effect Logic

• Formal Experiment Definition:

  • Formal Experiment: Research method that allows the researcher to manipulate the independent variable to study its effect on the dependent variable, providing conclusions regarding cause-and-effect relationships.

• Empirical Experimental Research on Media Violence:

  • Jean-Pierre Leyens Experiment (1975): Incarcerated delinquent boys in a detention facility were shown violent films (Westerns and war films) or neutral films over several days. Blind observers logged instances of verbal and physical aggression.

    • Result: Boys who viewed violent films exhibited significantly higher physical and verbal aggression over the subsequent $2$ weeks.

*   **Wendy Josephson Experiment (1987):** $400$ non-delinquent boys aged $6\text{–}8$ viewed a violent police film or a nonviolent film, were intentionally frustrated by a broken cartoon setup, and were observed during a floor hockey game.

    *   *Result:* Boys exposed to the violent film committed significantly more acts of aggression during the hockey game, successfully replicating Leyens' findings.

*   **Predisposition Effect:** In both studies, the violent film effect was markedly stronger in boys rated as aggressive prior to the experiment, indicating media violence exerts its largest causal impact on individuals predisposed to violence (Anderson, Lindsay, & Bushman, 1999; Anderson & others, 2001, 2003; Konijn & others, 2007; Paik & Comstock, 1994).

• Key Elements of Experimental Design:

  • Independent Variable: Variable whose quantitative value is independently controlled and manipulated by the experimenter (e.g., type of film shown: violent vs. nonviolent).

  • Dependent Variable: Variable whose quantitative value is measured to determine if it depends on the effects of the independent variable (e.g., measured level of aggression).

  • Experimental Group: Group in an experiment exposed to the active condition of the independent variable.

  • Control Group: Group in an experiment exposed to an inactive or nonviolent baseline condition of the independent variable, used for direct comparison.

• Mandatory Requirements for Valid Experiments:

  1. Random Assignment: Requirement that participants be assigned randomly to experimental conditions (e.g., drawing names from a hat) to equalize groups across all extraneous participant characteristics.

  2. Experimental Control: Requirement that all alternative explanations for differences in the dependent variable are strictly ruled out by holding all extraneous variables constant across conditions (e.g., ensuring both groups watch some film, keeping time of testing consistent).

Advanced Experimental Controls: Placebo and Blind Protocols

• Placebo Controls:

  • Placebo Effect: Changes in behavior produced by an inert or inactive condition in a formal experiment (e.g., inactive sugar pill, pseudo-psychotherapy session).

  • Medication Research Control: Control groups are administered identical-looking inert placebo pills to isolate the genuine pharmacological effect from participant expectations.

  • Psychotherapy Research Control: Control groups receive mock therapy sessions that mimic therapeutic interaction but exclude the explicit active therapeutic ingredient (e.g., discussing fears without step-by-step elevator exposure).

• Blind and Double-Blind Protocols:

  • Blind Experiment: Formal experiment in which the researchers recording dependent variable data are kept unaware of which participants are in the experimental or control group.

  • Reasons for Blind Protocols:

    1. Prevents Expectancy Bias: Prevents researchers from unintentionally interpreting ambiguous behavior in favor of their hypothesis.

    2. Eliminates Experimenter Bias: Experimenter Bias consists of subtle, unintentional influences on the dependent variable caused by experimenters interacting differently with experimental versus control participants (Basoglu & others, 1997).

  • Double-Blind Experiment: Experiment in which neither the researchers measuring outcomes nor the study participants know group assignments, providing maximum experimental validity.