3.11 - Measures of Stress
Biological measures of stress
Stress can be measured through various biological indicators that reflect the body's physiological responses. These measures focus on changes in heart activity, brain function, and hormone levels, providing objective data about stress.
Heart rate
Heart rate refers to the number of heartbeats per minute.
Effects of stress on heart rate:
- In acutely stressed individuals, heart rate increases.
- In chronically stressed people, heart rate may decrease, as shown in research by Schubert et al. (2009).
Heart rate variability (HRV)
Heart rate variability (HRV) is the variation in time intervals between consecutive heartbeats, measured in milliseconds with an electrocardiogram (ECG).
How HRV responds to stress:
- When a person is relaxed, HRV increases.
- Under stress, HRV decreases.
- Modern technology, such as smartwatches, can measure HRV optically by detecting blood flow waves in the wrist and transmitting data to a smartphone app.
Brain function using fMRI
Functional magnetic resonance imaging (fMRI) is a scanning technique that uses powerful electromagnets to measure brain activity by detecting changes in blood oxygenation and flow associated with neural activity. Areas of the brain with higher neural activity appear in different colours on the scan, highlighting regions activated during stress.
Salivary cortisol tests
Cortisol is a hormone released by the adrenal glands as part of the 'fight or flight' response to stress.
Features of cortisol testing:
- High levels of cortisol in saliva or urine indicate ongoing stress.
- This test is non-invasive.
Psychological measures of stress
Psychological measures assess stress through individuals' self-reported experiences and behaviours. These are subjective but convenient, often using questionnaires to gauge perceived stress levels.
Self-report questionnaires
Self-report questionnaires are tools where individuals rate their own stress levels or experiences, typically through structured questions. They are easy to administer and complete.
Friedman and Rosenman's personality test
Friedman and Rosenman developed a method to identify personality types linked to stress and heart disease risk.
Development of the test:
- They initially sent questionnaires to 150 San Francisco businessmen and hospital workers, asking about habits observed in friends or patients before heart attacks, identifying consistent traits.
- Over more than eight years, they conducted structured 25-question audio-taped interviews assessing responses to everyday pressures, with ratings by two researchers for inter-rater reliability.
- This led to classifying personalities as Type A or Type B.
Jenkins et al. (1979) adapted this into the Jenkins Activity Survey, a pen-and-paper questionnaire with 21 items best predicting Type A behaviour, such as questions on punctuality and competitiveness. This allows psychologists to categorise individuals efficiently.
Life events questionnaire
Life events questionnaires measure stress by quantifying major changes in a person's life. Holmes and Rahe (1967) created the Social Readjustment Rating Scale (SRRS), which lists 43 life events based on patient reports.
How the SRRS works:
- A sample of 394 participants rated these events for the adjustment required, regardless of whether positive or negative, leading to ranked scores.
- Total scores over a 12-month period predict stress-related illness risk:
- Fewer than 150 life change units: 30 per cent chance of stress.
- 150–299 life change units: 50 per cent chance of stress.
- Over 300 life change units: 80 per cent chance of stress-related illness.
Research studies on measures of stress
Key studies demonstrate how biological and psychological measures are applied in real-world contexts.
Wang et al. (2005)
This study aimed to examine the neural circuitry involved in psychological stress using fMRI.
Method:
- 32 participants: 25 in the experimental group and 7 in the control group.
- Experimental group underwent perfusion fMRI scans in four eight-minute sessions: baseline (no task), low-stress (counting backwards from 1000 aloud), high-stress (serial subtraction of 13 from a four-digit number aloud, with prompts to speed up and restart on errors), and final baseline.
- Control group had similar scans but no tasks.
- All participants completed a self-report stress scale (1-9), provided saliva samples for cortisol before and after scans, and experimental participants rated effort, frustration, and difficulty.
- Heart rate was recorded every two minutes.
Results:
- The ventral right prefrontal cortex (RPFC) showed sustained activation during and after stress tasks.
- Perfusion fMRI effectively measured stress-related brain changes.
Conclusions:
- The ventral RPFC plays a key role in the stress response.
Evans and Wener (2007)
This study investigated how passenger density and proximity on trains affect commuter stress.
Method:
- 208 American commuters completed five-point Likert scales to report stress during morning commutes.
- Near journey's end, they did a proofreading task to measure motivation and persistence.
- Saliva samples measured cortisol at journey's end, with a weekend home sample for comparison at the same time.
- Crowding was observed directly.
- Spouses or partners rated commuter interactions on a five-point scale via questionnaire.
Results:
- Proximal crowding correlated significantly with higher cortisol, poorer mood, and more proofreading errors.
- Distal crowding showed no stress correlation.
- Longer commutes linked to higher cortisol, worse proofreading, and greater perceived stress.
- Spousal ratings did not correlate with commute length.
Conclusions:
- Proximal crowding increases stress, likely due to personal space invasion, while distal crowding does not.
Methodological issues in measuring stress
Measuring stress involves both strengths and weaknesses, depending on the method used.
| Strengths | Weaknesses |
|---|---|
| Generalisability - The Jenkins Activity Survey is an easy-to-score self-report questionnaire; it could be completed online or sent out to large numbers of people. | Generalisability - Wang et al.'s (2005) fMRI research was expensive and time-consuming, and there were just 32 participants, giving low generalisability. |
| Validity - Scully et al. (2000) reviewed the SRRS 30 years after it was first used. They reported it was still a reliable measure of life events, stress, and ill health, suggesting it has temporal validity. | Validity - Holmes and Rahe's (1967) research was correlational, only looking at the relationship between health and life events. There could be other variables (like poor nutrition through stress) affecting health. |
| Objective data - Evans and Wener (2007) measured cortisol in saliva samples; this is an objective way of measuring physiological effects of stress. Wang et al. used fMRI scans, which is a more objective and reliable way of measuring stress than self-report methods. | Subjective data - Self-report measures of stress or personality (Friedman and Rosenman, 1974; Holmes and Rahe, 1967) are prone to social desirability bias. |
Issues and debates in stress measurement
Stress measures raise broader psychological questions about individual differences and cultural influences.
Individual and situational explanations
Many stress scales, like the SRRS, adopt an individualist approach, attributing stress and illness to personal behaviours and life events. This fails to consider lifelong environmental stressors like disability or poverty.
Cultural differences
Research on stress measures often reflects a Western, individualist perspective, assuming events like Christmas, weddings, or moving house are universally stressful. These assumptions have not been tested cross-culturally.