PSYCH307 – Lecture 2 Notes

Overview of Psychological Measurement

Psychological measurement / assessment is defined as the systematic gathering and integration of psychology-related data for the purpose of making an evaluation about a person. Authoritative definitions (Cohen & Swerdlik, 2018; APA Dictionary of Psychology; New Zealand Psychologists Board) converge on three ideas: (1) multiple data sources (tests, interviews, observations, specialised apparatus) are permissible; (2) the goal is diagnostic, predictive, or treatment-oriented; and (3) the procedures must be structured and standardised. All psychometric tests therefore aim to quantify aspects of human functioning in a reproducible way.

Components of Psychological Measurement / Assessment

Psychological assessment has two inseparable components:

1. Physiological measurement – direct recording of bodily processes (e.g., heart rate, electro-dermal activity, brain waves).

2. Psychometric measurement – indirect estimation of latent psychological constructs through standardised behavioural or self-report instruments.

Psychophysiological Measures

Psychophysiology studies links between subjective experience (thoughts, feelings, emotions) and measurable bodily changes. Whenever we experience highs or lows, the autonomic and central nervous systems adjust in predictable ways that can be captured with sensors.

The Human Autonomic Nervous System (ANS)

The ANS orchestrates involuntary processes such as heart rate, respiration, and digestion. It has two complementary branches:

• Sympathetic nervous system – mobilises energy in the face of real or perceived threat (the classic "fight-or-flight" reaction). Typical signs are increased heart rate, elevated blood glucose, and redistribution of blood toward skeletal muscles.

• Parasympathetic nervous system – conserves energy during safety ("rest-and-digest"). It slows the heart, enhances peripheral circulation, and promotes digestion and restoration.

Physiological Indices Commonly Recorded

• Electrocardiogram (ECG/EKG) and heart rate.

• Skin conductance level / response.

• Respiration patterns.

• Peripheral (e.g., limb) temperature.

These indices are proxies for sympathetic or parasympathetic dominance at any given moment.

Electrocardiogram (ECG) & Heart Rate

Electrical depolarisation followed by synchronised myocardial contraction produces a strong field detectable by electrodes. Chest placement maximises signal-to-noise, whereas wrist placement introduces muscle artifacts. Heart rate (HR) is derived from the inter-beat interval (IBI); peak-to-peak distances converted to beats-per-minute give instantaneous or averaged HR values. Generally, HR rises with sympathetic arousal and falls with parasympathetic relaxation.

Electrical Skin Conductance

Sweat-gland activity modulates the skin’s conductance. Micro-siemens changes index emotional arousal irrespective of valence. Because polygraphs employ skin conductance and cardiovascular measures, they are highly reliable (they repeatedly detect arousal) yet display poor validity for lie detection – they measure arousal, not veracity, so innocent nervous participants can fail and calm deceivers can pass. Historical anecdote: Roy Post (1939) humorously demonstrated that a kiss could confound the polygraph.

Respiration

A stretch belt around chest or abdomen records expansion. Amplitude (height A) reflects depth, and period (distance B) reflects frequency. Relaxation typically manifests as <12 breaths-per-minute with diaphragmatic dominance, whereas thoracic breathing accompanies stress.

Limb Temperature

Thermistors detect changes smaller than $0.001^{\circ}$. Sympathetic vasoconstriction lowers peripheral temperature under stress; parasympathetic rebound raises it during relaxation. Biofeedback protocols often use hand-temperature training.

Neurophysiological Measurement – Electroencephalography (EEG)

Scalp electrodes, referenced to an inactive site (e.g., mastoid), register summed post-synaptic potentials of thousands of neurons. Waveforms are expressed in millivolts over time and cluster into frequency bands associated with mental states:

• Gamma (30–100 Hz): high-level cognition, conscious problem-solving.

• Beta (13–30 Hz): alert, externally focused processing.

• Alpha (8–12 Hz): relaxed wakefulness, eyes closed.

• Theta (4–7 Hz): drowsiness, light sleep, meditation.

• Delta (<4 Hz): deep, slow-wave sleep.

Pupillometry

Pupil diameter changes (mydriasis) are sensitive not only to illumination but also to emotional arousal and cognitive load. Modern eye-trackers therefore infer mental effort in tasks ranging from memory to decision-making.

Advantages and Limitations of Physiological Measures

Advantages

• High reliability and temporal precision.

• Immune to self-report bias.

• Offer a holistic view across bodily systems.

Limitations

• Validity can be ambiguous – the same arousal signature can stem from joy or fear.

• Complex constructs (e.g., perfectionism) remain inaccessible.

• Large inter-individual variability complicates normative comparison.

Illustrative Research Example – “Arrow of Time”

Time flows directionally (eggs break but do not unbreak). Using pupillometry, researchers examined whether people dislike sequences that violate chronological order (e.g., hungry→eating reversed) and whether individual time-perspective modulates cognitive resource allocation.

Why Self-Report Measures Remain Necessary

Neuroscientist Benjamin Libet argued that conscious mental phenomena cannot be read directly from neural firings; only first-person reports reveal subjective qualia. Hence, psychometrics complements physiology.

Assumptions Underpinning Psychological Measurement

1. Psychological states/traits exist and are measurable.

2. Behaviour in a test context predicts behaviour elsewhere.

3. Every test possesses strengths and weaknesses.

4. All measurements include error $\text{Observed score} = \text{True score} + \text{Error}$.

5. Fair, unbiased testing is possible.

6. Quality tests ultimately benefit individuals and society.

Psychometrics – “Measuring the Soul”

Psychometrics is the statistical science of quantifying latent constructs such as Future Time Orientation, Quality of Life, Intelligence, Anxiety, Self-Esteem, Assertiveness, or Optimism. Because these variables are not directly observable, instruments rely on manifest indicators (items) to infer latent variables.

Examples of Widely Used Scales

1. Five Facet Mindfulness Questionnaire (FFMQ; 39 items across Observing, Describing, Acting with Awareness, Non-Judging, Non-Reacting).

2. Depression Anxiety Stress Scales (DASS-21; 0–3 Likert responses).

3. Perceived Stress Scale (PSS-10), cited >17,000 times.

Criteria for Selecting / Developing a Scale

1. Validity – Does it measure the intended construct?

2. Reliability – Are scores precise, internally consistent, and capable of discriminating individuals?

3. Responsiveness – Can it detect clinically meaningful change?

4. Utility – Is it practical (time, cost, readability, user burden)?

Fundamental Principles of Measurement

• Invariance – Equal units across populations.

• Unidimensionality – One construct per scale.

• Validation employs advanced models such as Item Response Theory, Rasch Measurement, and Generalisability Theory (pioneered by Thurstone and Rasch).

Classical Test Theory (CTT)

The dominant 20th-century framework emphasises correlations among items and total scores. Key statistics include item–total correlations, Cronbach’s $\alpha$, McDonald’s $\omega$, and exploratory/confirmatory factor analysis.

Types of Validity

• Face Validity – Surface plausibility (e.g., “I feel sad” in a depression test).

• Content Validity – Comprehensive coverage (algebra, geometry, calculus in a math battery).

• Predictive Validity – Forecasting future outcomes (IQ predicting GPA).

• Concurrent Validity – Correlation with simultaneous gold-standard (new anxiety scale vs. established scale).

• Convergent Validity – Agreement with alternative measures of same construct (self-report empathy vs. peer ratings).

• Discriminant Validity – Low correlation with unrelated constructs (self-esteem vs. motor coordination).

Types of Reliability

• Test–Retest – Stability over time for traits; correlation of Time 1 and Time 2 scores.

• Internal Consistency – Homogeneity of items. $\alpha$ or $\omega$ between $0.70$ and $0.95$ is acceptable, noting inflation with many similar items.

• Intra-Scorer – Same rater, different occasions.

• Inter-Scorer – Different raters assessing the same target.

Variables and Levels of Measurement

Discrete Variables

• Quantitative (integer counts): number of students, goals.

• Qualitative (categorical): gender, ethnicity; numbers may serve as labels only.

Continuous Variables

• Quantitative measures with infinite gradation: height, reaction time, temperature.

Measurement Scales

• Nominal – categories only (eye colour); no ordering, no true zero.

• Ordinal – ranked categories (race position); unequal intervals.

• Interval – equal spacing but arbitrary zero (temperature $^{\circ}C$, IQ).

• Ratio – equal spacing with absolute zero (age, reaction time).

Specificity increases from nominal to ratio, but appropriateness depends on research design, not "better vs. worse".

Conclusion – Integrating Physiology and Psychometrics

Using both physiological indices and psychometric instruments enhances assessment accuracy, controls response bias, distinguishes valence in arousal, and clarifies how subjective experience interfaces with bodily processes—vital insights for health and well-being.

Acknowledgements & Closing

Lecture delivered by Professor Taciano L. Milfont (University of Waikato) on 14 July 2025. Slides concluded with “Obrigado! / Thank you! / Kia ora!” and university contact information.