To describe how different variables contribute to psychological aging throughout human life, we trained DNNs on MIDUS 1 age group subsamples (25-39, 40-64, 65-75 years). These models contained the same 50 features as PsychoAge and Subjage, but their relative importance was not constant. In other words, a variable’s contribution to psychological aging was not static and its influence may vary with time.
First, we explored important variables (top-25 mean normalized PFI and DFS scores) shared by all age-group specific clocks to define the “psychological aging core” – features that significantly shift throughout one’s lifespan ( Table 2 ). Core features that determined the chronological aspect of psychological aging in MIDUS 1 contained neuroticism, seeing the community as a source of comfort and defining the lower boundary of male middle age. These features are expected to have life-long trends that let DNNs tell an old and a young person apart. Personality traits that were rendered important for human perception of age included aspirations scale, extraversion, openness, being career-oriented, and the prevalence of the positive reappraisal coping mechanism. Changes in these traits are expected to drive the internal psychological clock in humans of all ages.
Table 2
Effort put in life overall; Lower aspirations; Forcefulness; Current opinion about contributing to the well-being of others. Live for today; Persists in goal striving; Positive re-appraisal; Highest level of education; Current opinion about health. Now taking prescription medications for blood pressure; Marital status; Headaches frequency (30 days); Body mass index; Define age when men enter middle age; Community is a source of comfort; Neuroticism; Conscientiousness; Opinion about control of life in general; Define age women enter middle age; Mental health (self-evaluated); Sex life expectations in 10 years; Health locus of control – others; Highest level of education; Contributing to the well-being of others in 10 years; Chronic conditions (12 months). Effort put in contributing to the well-being of others in 10 years; Opinion about life in general; see the site Effort put in health; Neuroticism. Body mass index; Lower aspirations; Extraversion; Rate work situation in 10 years; Effort put in work; Positive reappraisal.
A series of DNNs was trained using samples from specific age groups (25-39, 40-64, 65-75 years) to inspect which features get recognized as important only within these groups. Features used by any model are the same 50 features as in SubjAge and PsychoAge; unique important features are defined as the features present in the top-25 importance list for only one aging clock. MAE stands for “Mean Absolute Error” See Supplementary Table 2 for a more detailed report.
Define age women enter middle age; Middle age upper limit (male); Current opinion about work situation; Contributing to the well-being of others in 10 years; Made unique contributions to society; Current opinion about life overall; Current over life in general at present; Current opinion about sexual aspects of life
The psychological core defines what aspects of human personality are constantly evolving and thus qualify as lifelong markers of psychological aging. But some features may quickly shift in a certain life period and be important for measuring psychological aging in this period only. These variables are called “uniquely important” in Table 2 . They identify which aspects of psycho-social life change the most reliably within an age group and thus get assigned higher importance within the corresponding age predictor.
To illustrate, agency is a uniquely important feature for accurate chronological age estimation in elderly people. This does not mean that being more or less willing to shape one’s own life is a trait only seen (or uniquely lacking) in the elderly. Most probably, agency was considered important in this age group, since people experience a major shift in this psychological attribute while going from 65 to 75 years. The DNN may have learned this possibly non-linear pattern to move a person closer to the upper or the lower boundary. In contrast, younger people may maintain more consistent agency throughout their lives, which makes DNNs seek aging-related patterns in other features.
