Introduction
Definition and measurement of subjective mood state
Measure | Scales | Strengths and weaknesses | Reliability (Cronbach’s alpha [rα]) |
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Bond–Lader visual analogue scale (BL-VAS) [69] | Subscales for calmness (encompassing individual questions on the extent of relaxation or calmness), contentedness (encompassing the emotions contented, tranquil, happy, amicable and gregarious) and alertness (encompassing alert, strong, well-coordinated, energetic, quick-witted, attentive, proficient, interested and clear-headed) | Using specifically selected subscales of common mood states, such as calmness and contentedness, it fails to capture a wide spectrum of other emotions, such as anger, or mind states that might not be viewed as strictly emotion, such as confusion or guilt | All scales: rα = .77–.93 [70] |
The Positive and Negative Affect Schedule (PANAS) [71] | Ten positive affects (interested, excited, strong, enthusiastic, proud, alert, inspired, determined, attentive, and active) and ten negative affects (distressed, upset, guilty, scared, hostile, irritable, ashamed, nervous, jittery, and afraid) | When measuring moods after food consumption or relating to nutrition, such diverse emotions as hostility or pride may not be useful. Simply asking such questions can induce differential emotions | All scales: rα = .85–.90 [71] |
The Profile of Mood States (POMS) [72] | A measure of six dimensions of transient and distinct mood states. The subscales are: tension/anxiety, vigour/activity, depression/dejection, fatigue/inertia, confusion/bewilderment, and anger/hostility. A total negative mood score can also be computed by adding up the five negative mood subscales and subtracting the positive scale vigour/activity | Widely used in cross-sectional studies and found to discriminate between different habitual diets; used in acute and chronic studies of intake of specific nutrients, vitamins, minerals and herbal supplements | |
World Health Organization Quality of Life Scale [75] | Comprises 26 items, which measure the following broad domains: physical health, psychological health, social relationships, and environment | Unlikely to pick up acute effects of food, but might reflect influence of habitual dietary patterns | Physical domain: rα = .82; psychological domain: rα = .81; social domain: rα = .68; environmental domain: rα = .80 [76] |
The Satisfaction with Life Scale (SWLS) [77] | Comprises five items on satisfaction with life | Retrospective life experiences, may not be directly related to effects of diet | All scales: rα = .61–.81 [77] |
Subjective Happiness Scale (SHS) [78] | Four-item scale of global subjective happiness. Two items ask respondents to characterise themselves using both absolute ratings and ratings relative to peers, whereas the other two items offer brief descriptions of happy and unhappy individuals and ask respondents the extent to which each characterisation describes them | Measures only one dimension of mood, namely positive feelings | All scales: rα = .74–.94 [78] |
General Health Questionnaire (GHQ) [79] | Four subscales consisting of somatic symptoms, anxiety/insomnia, social dysfunction, and depression. (Multiple versions differing in number of items: GHQ-60, 30, 20, 28. 12) | Validated as a tool to assess mental health in large population samples; symptoms may be enduring and less likely to vary in relation to transient nutritional induced changes in subjective state |
Validity of measures of subjective states
Detection and interpretation of meaningful effects
Expectancy and placebo effects
Relationships between subjective and objective mental performance measures
Linking subjective states to mechanisms of action
Recommendations and conclusions
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Consideration of both traditional mood questionnaires or the use of ecological momentary assessment (EMA) or experience sampling methods (ESM), which may more realistically capture transient mood states. Identifying which are best and most reliable under which condition.
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Use measures sufficiently sensitive to detect effects of a nutritional manipulation and to evaluate the magnitude and meaningfulness of changes demonstrated, e.g. by comparison with effects induced by drugs or alcohol or variations in mood which occur over the course of a day.
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Consider the possibility that subjective and objective measures will occur within different time frames and in response to different doses. Acute on chronic studies may help capture transient effects on mood or cognitive function which may result in longer-term measureable benefits.
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Recognition of the importance of expectancy and placebo effects when measuring subjective mood states and behaviour generally and selection of well-matched placebos.
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Demonstrating biological plausibility is crucial when linking the effects of specific nutrients to subjective mood states and behaviour.