Table 1.
Apathy-Motivation Index (AMI, provided in S1 Appendix).
Table 2.
Participant characteristics.
Table 3.
Descriptive statistics of related measures.
Fig 1.
Apathy Motivation Index (AMI) factor model.
The factor analysis identified three distinct subscales, namely behavioural activation (BA), social motivation (SM) and emotional sensitivity (ES). BA relates to an individual’s tendency to self-initiate goal-directed behaviour, SM examines a person’s engagement of social interactions and ES probes an individual’s feelings of positive and negative affection. While SM correlated with BA and ES, BA did not associate with ES. (**: p < 0.01).
Table 4.
Proposed cut-offs for moderate (> 1S.D.) and severe (> 2S.D.) apathy on AMI.
Table 5.
Relationship between AMI score and established measures of apathy (clinical indices), depression, anhedonia and fatigue.
Fig 2.
Correlation coefficients between AMI subscales and established measures of depression, anhedonia and fatigue.
BA and SM correlated positively with BDI and MFIS, indicating that individuals that were more apathetic on these subscales also had higher levels of depression and fatigue. In contrast the ES scale was negatively correlated with depression and fatigue. All three AMI subscales were negatively correlated with the SHAPS (lower scores indicate higher levels of anhedonia), suggesting that higher apathy was associated with lower hedonia.
Table 6.
Latent Profile Analysis (LPA) Model fit indices.
Table 7.
Overall sample means and AMI profile conditional response means on the AMI Behavioural Activation, Social Motivation and Emotional Sensitivity subscales.
Fig 3.
Distribution of apathy along the AMI subscales and conditional response means of the 4-class solution.
The AMI consists of three subscales: Behavioural Activation, Social Motivation and Emotional Sensitivity. Every subscale contains 6 items that is each scored from 0–4, with a higher mean score indicating greater apathy. (A) 3D scatterplot illustrating the distribution of each healthy individual’s mean rating along the three AMI subscales. The four classes were labelled generally motivated (orange), behaviourally/socially apathetic (green), emotionally apathetic (blue), and generally apathetic (red). (B) Conditional response mean value greater than overall sample means (black line) indicates apathy on that AMI subscale.
Fig 4.
Relationships between apathy subtype and depression, anhedonia and fatigue.
The four apathy-motivation subtypes were predictive of different associations with depression (A), anhedonia (B) and fatigue (C). The behaviourally/socially apathetic experienced the greatest depression and fatigue while the generally motivated were most hedonic. (* p < 0.05, ** p < 0.01, *** p < 0.001).