Below is a categorized list of core constructs—latent physiological, behavioral, cognitive, and environmental processes—that researchers map onto digital proxies when studying serious mental illnesses (SMI). Each of these constructs captures a facet of daily functioning or physiology that’s often disrupted in schizophrenia, bipolar disorder, and severe depression.

Approach: I am starting from clinical constructs to explain their relevance, and then finding associations to digital phenotyping studies. Next, I want to determine appropriate thresholds—what constitutes "high" or "low" values for these measures.

The Big So what question after this exercise?

1. Sleep, Mobility, Phone usage, HRV seems to be used most, repeatably across clinical constructs.
2. Most papers flag “relative drop or spike” as a meaningful early warning signals rather than a raw/fixed numbers.
3. Better to combine streams of signals; e.g Short Sleep hours + Late night screen time + increased burst of text messages / tapping predict ?mania?
4. DP are proxy, direct or indirect to clinical constructs.

Note:

This construct list was adapted from clinical symptom domains commonly observed in serious mental illness (SMI) and studied. It builds on domains identified in frameworks like the DSM-5, PANSS, PHQ-9. Some come from pathophysiological research. This list is not exhaustive, but reflects core constructs that are both clinically meaningful.

| **Constructs (What)

Core clinical symptom (assessed in all SMI) and research focus (e.g. actigraphy studies)

| Physiological | - Mania - Reduced total sleep time

• PTSD - fragmented sleep Fragmented sleep

• Bipolar - Less then 6 hours link to incipient mania

• Bipolar - Ongoing reduction of sleep 30% of baseline increase relapse risk

• Disturbed sleep spike before psychosis relapse

-PTSD associated with more disturbed sleep

• Bipolar - Irregular sleep-wake cycle associated with mood instability

• Irregularity of sleep hours (circadian phase) associated with mood. Going to bed later then usual - Depression. Going to bed earlier, waking up earlier - manic

• {Haven’t found paper on link between sleep and schizoprehnia}

• Later sleep onset and later waking times associated with poorer symptoms for SZ.

• Greater dysregulation in social rhythm (less routine) associated with higher symptom severity for SZ.

- Higher mean and standard devia- tion of sleep/wake ratio compared with healthy controls.

- Increased mean sleep/wake ratio predicted increased negative, but not positive, symptoms | - < 6 Hours - Bipolar indicate incipient of mania

• Sleep reduction 30%> of baseline in Bipolar increase risk (about 2 hours reduction in a 7 hours sleep duration over a few days)

• Screentime/Communication - Bipolar “excessive nighttime phone use can also disrupt sleep and trigger mood instability

• As a general intervention- “Early trials found that a 3-week reduction in screen time actually improved depression and sleep quality, highlighting its clinical relevance”

• • Bipolar mania “bipolar manic episodes were accompanied by a jump in phone call frequency and text activity, alongside insomnia” | 1. Sleep is definitiely an important DP

2. Current logic of looking for changes in sleep hours, sleep segments can work,
3. So far mostly about bipolar disorder. Reduce sleep = Mania
4. Trauma/Anxiety = more disturbed sleep | Sensor: - Sleep (Fitbit)

• Socialbility (Text/Calls)

• Screen Time

• FITBIT Collect Sleep Hours, Sleep Stages | | …Appetite & Weight Changes | significant loss or gain in appetite/weight (seen in depressive episodes and other SMI)

Both – Monitored clinically as a symptom (especially in mood disorders) and studied in research (e.g. metabolic health in SMI) | Physiological | No Sensor | | | Not using | | …Energy Level Dysregulation | fatigue/low energy in depression vs. increased energy in mania

Low energy is a clinical criterion in depression ; mania features high energy, and activity levels are tracked in research

Research – Biomarker of stress reactivity; frequently observed in depression and sometimes in psychosis (not routinely measured clinically). | Physiological | - In direct proxy - Based on accelerometer, GPS, and phone use log | | | | | Inflammation Markers | elevated inflammatory cytokines or CRP in subsets of patients

Biological indicator linked to depression, bipolar, and schizophrenia pathophysiology (investigational, not part of standard clinical assessment). | Physiological | - There is this VitaPatch Proof of concept | | | | | Autonomic Arousal  | e.g. heart rate variability reduction due to chronic stress/anxiety in SMI

Research - Measured via physiological sensors; reduced HRV is found in schizophrenia, bipolar, and depression compared to controls | Physiological | - Lower HRV indicates higher stress or mood instability

• Bipolar Disorder — HRV (RMSSD) was markedly lower during mania compared to the same patients’ euthymia (within-subject drops with large effect sizes, Cohen’s g ~1.0)

• Mood Disorder - “Meta-analyses confirm **chronically blunted HRV in mood disorders”**

• Schizophrenia - Meta analysis found a reduced HRV across a range of psychiatric conditions, not just BD, with psychotic disorders featuring the greatest reduction. (Cite 13-16 source from here)

• In schizophrenia, RR SDNN was negatively correlated with positive symptoms (rho = -0.50, p = 0.007), indicating that lower HRV reflects worse symptoms

- increased variability in HRV features associated with SMI status. | - “on the order of a 30–50% reduction in RMSSD in some cases” before mania relapse

• HRV was lower in the manic state when compared to the euthymic state for all HRV metrics (p ≤ 0.02), with large to medium effect sizes (g = 1.24 to 0.65). HRV changes were not significantly affected by age or sex.

-13https://www.nature.com/articles/s44184-024-00090-x?error=cookies_not_supported&code=3591ce40-ba82-4c5f-a540-d71a84f101f8#:~:text=Bipolar%20disorder%20,the%20sample%20size%20limited%20the | 1. SMI generally have lower HRV? As if people with SMI are stuck in low HRV? 2. Tracking HRV, when lower = Increase stressors 3. Lower HRV = Mania 4. Use this to trigger EMA?

?What is a low HRV?

So far it only find correlations. not direct links | **Sensors

1.** Fitbit (HRV) | | Social Withdrawal/Isolation | disengagement from social interactions (common early feature of psychosis, also in depression)

Both – Clinically evident (patients withdrawing from friends/family) and tracked in research (as a transdiagnostic early warning sign) | Social | Mobility/Activity Sensors

• Schizophrenia “individuals with schizophrenia traveled significantly less distance per day than healthy controls (median ~7 miles from home vs 12 miles in controls) and spent more time at home (77% of time vs 63% in controls)”

Mobility/Activity Sensors - Bipolar Disorder — “one digital phenotyping study noted that on days distance traveled fell well below a patient’s average (e.g. staying within a one-block radius), their depression severity (PHQ/PANSS scores) was worse”

Screentime and Communication — Bipolar - “longer daily screen time was significantly associated with worse depressive symptom severity”

Screentime and Communication - Bipolar Depression - “Patients in bipolar depression spent more time on their phones on average, and their total screen minutes per day correlated positively with depression scale scores.” | Schizoprehnia - 30% reduction in step count or location variance is considered abnormal and potential predictive of relapse into depression or social withdrawal

Bipolar Depression - “a rule of thumb used in some digital apps is that a sudden increase in screen time by >1–2 hours/day (especially at odd hours) could indicate a depressive downturn” | 1. Reduction in acvities/GPS could indicate withdrawal, depression. 2. Cross reference to screen time, whether increased? also can be proxy for mood issues. | **Sensor

1**. Fitbit (Steps) 2. Phone (Steps) 3. GPS 4. phone screen time | | Functional Impairment (Social/Occupational) | difficulties in work, school, or independent living across SMI

Both – A hallmark of SMI in practice (measured by global functioning scales) and outcome in research (often remains impaired even during symptom remission) | Social | - Indirectly via GPS, Travel time, Sleep timing - “High accuracy in the “employment” subscale suggests metrics like consistent morning location (work vs. home) and mobility patterns can indicate whether someone is holding a job” - | | | | | Social Cognition Deficits  | impairments in understanding others (e.g. theory of mind, emotion recognition) Research – Documented in schizophrenia and bipolar (though more severe in schizophrenia) ; targeted by social skills training, but not routinely measured in general clinical exams. | Social | No Sensor | | | | | Loneliness / Low Social Support | subjective feeling of being alone or lacking support network

Both – Frequently reported by SMI patients and associated with worse outcomes (e.g. loneliness correlates with higher risk of psychosis, bipolar episodes, and depression) . Addressed in psychosocial interventions and studied epidemiologically. | Social | - Combined GPS, accelerometer, call/SMS; Bluetooth proximity - https://mhealth.jmir.org/2022/4/e34638 (Scoping review of 29 studies: 69 % used phones/wearables; most achieved ≥70 % accuracy classifying high-loneliness using mobility + communication features, with validated loneliness scales as ground truth) | | 1. Hmmm not reliable yet | | | Stigma and Discrimination | experiences of social stigma related to mental illness. Research – Not a direct symptom, but pervasive across SMI, leading to isolation and reduced help-seeking . Addressed indirectly in psychoeducation and advocacy (important for recovery outcomes). | Social | No Passive Sensor | | | | | Family Stress / High Expressed Emotion | family environment marked by high criticism, hostility, or over-involvement.

Both – High expressed emotion in relatives predicts higher relapse rates in schizophrenia and mood disorders . Clinically, family interventions aim to reduce this stress, and it’s a well-established research construct. | Social | No Passive Sensor | | | | | Trauma History (Adverse Childhood Experiences) | e.g. childhood abuse or neglect, which elevates risk for SMI

Both – Clinicians assess trauma due to its impact on course of illness, and research shows childhood trauma increases likelihood and severity of schizophrenia, bipolar, and depression | Social | No Passive Sensor | | | | | Socioeconomic Adversity | poverty, unemployment, housing instability often intertwined with SMI

Both – Considered in psychosocial assessments (SMI can lead to job loss and poverty, and vice versa) . Frequently studied as social determinants of mental health outcomes. | Social | No Passive Sensor | | | | | Cognitive Impairment | deficits in attention, memory, and executive function present across SMI

Both – Clinically, patients show objective cognitive deficits (e.g. poor concentration, memory issues) and research robustly confirms pervasive neurocognitive impairment in depression, bipolar, and schizophrenia | Behavioral | -Communication/Texting — Mania - “Typing dynamics can even change – e.g. rapid, error-filled texting has been observed before manic relapses (Arevian et al., 2020)” | | 1. Increased in error-filled texting (can we detect that?) number of times backspace entered? or typo? = Mania? | **Sensors

1. Tapping speed** | | Anhedonia | loss of ability to experience pleasure or interest (common to depression and negative symptoms of schizophrenia)

Both – Core clinical symptom in major depression and schizophrenia , and extensively studied in research (e.g. reward processing deficits). | Behavioral | No Passive Sensor | | 1. Use Active input - Mood Log | | | Avolition | lack of motivation or drive to initiate and persist in activities (seen in schizophrenia and severe depression)

Both – Clinically recognized (especially as a negative symptom in psychosis) and linked to functional disability ; also investigated in research on motivational deficits. | Behavioral | Mobility/Activity - “lower mobility correlated with greater negative symptom severity (especially apathy and amotivation)” | | 1. Reduce activities = negative symptoms? Then cross reference to see if sleep hours changed? | **Sensor

1. GPS** | | Depressed Mood | pervasive sadness or low mood (appearing not only in MDD but also as comorbid depression in schizophrenia and bipolar)

Both – Primary clinical symptom in depression; also frequently co-occurs in schizophrenia (up to ~50% experience depressive episodes) and in bipolar disorder. Widely studied in all these disorders. | Behavioral | Mobility/Activity - Bipolar Depression - “in bipolar depression, passively sensed activity tends to drop: fewer steps, more sedentary hours, and shorter travel distances have all been associated with higher depression scores”

Communication - Bipolar Disorder - “Passive phone logs in bipolar disorder show that during depression, patients initiate fewer outgoing calls and answer fewer incoming calls, proportional to depression severity. | As a general intervention- “Early trials found that a 3-week reduction in screen time actually improved depression and sleep quality, highlighting its clinical relevance” | 1. Reduced activity, reduced travel distance = higher depression 2. Reduced outgoing calls, fewer answered incoming calls = depression

3. Can create a mini-challenge to encourage 3 weeks of reduce screen time to improve depression and sleep quality | **Sensor

4. GPS

5. Socialbility (Calls/Text)

6. Screen time** | | Anxiety Symptoms | excessive worry, fear, or physiological anxiety (often comorbid across SMI diagnoses)

Both – Clinicians often find anxiety in schizophrenia, bipolar, and depression (e.g. >38% of schizophrenia patients have significant anxiety symptoms) . Anxiety is also a transdiagnostic research focus (e.g. treatments targeting anxiety across disorders). | Behavioral | - Many papers - https://pubmed.ncbi.nlm.nih.gov/38807465/ (need deeper study) | | | | | Irritability/Anger | proneness to anger and irritability (notable in bipolar mania, depression, and even some schizophrenia cases)

Both – Assessed clinically (irritable mood can signal a depressive or manic episode) and included in cross-cutting symptom measures . Research examines irritability as a cross-diagnostic dimension. | Behavioral | Mood State maybe possible..? | | | | | Emotional Dysregulation (Mood Lability) | difficulty regulating emotions, with rapid or intense mood swings

Both – Seen in various disorders (e.g. mood lability in psychosis spectrum and bipolar is elevated and tied to worse social outcomes ). Addressed in therapies (DBT, etc.) and studied as a transdiagnostic process. | Behavioral | - Mania - “Longer distances traveled were associated with higher manic symptom severity”

• Mania - “during manic states, patients often exhibit a flurry of communication: one study found more frequent outgoing text messages (and unusually short, terse replies from others) correlated with higher mania ratings”

• Bipolar mania “bipolar manic episodes were accompanied by a jump in phone call frequency and text activity, alongside insomnia” | -Schizoprehnia - 30% reduction in step count or location variance is considered abnormal and potential predictive of relapse into depression or social withdrawal

• Mania - “watch for sudden spikes in activity (e.g. a sharp increase in daily steps or outings by >50% above baseline) as a warning of mania” (Citation needed)

• look for “an elevated activity level for several days coupled with reduced need for sleep, which reliably predicted impending manic mood shifts (AUC ~0.98 for mania prediction using actigraphy)”

• Screentime/Communication - Bipolar “excessive nighttime phone use can also disrupt sleep and trigger mood instability | 1. Increase distance travel associated with mania

2. Increased communication = mania

3. Sudden lncrease of call frequency = mania

4. Reduction of activities, location = depression = social withdrawal

5. Increase screentime at night - can be a EMA (= distrup sleep, and next day mood instability) | Sensors

6. GPS

7. Socioability

8. Fitbit (Steps)

9. Phone usage - screen time

10. Sleep | | Psychotic Symptoms (Hallucinations & Delusions) | perceptual distortions and false beliefs that can occur in schizophrenia, but also in severe mood disorders

Both – Hallucinations and delusions are core clinical features of schizophrenia and schizoaffective disorder, and can emerge in bipolar mania or severe depression with psychotic features . Research examines these symptoms’ mechanisms across diagnoses. | Behavioral | - Mobility/Activity - Schizophrenia - “Less GPS mobility was related to greater negative symptom severity, particularly diminished motivation,”

-Communication - In schizophrenia, reduced social calls or messages often precede relapse; one mobile health study noted that days with no communication activity spiked in the week before a psychotic relapse | - Schizophrenia - “The rate of behavioral anomalies (e.g. unusually low movement for that person) in the 2 weeks preceding a relapse was ~71% higher than during stable periods”

• Schizophrenia - “combined anomalies in mobility and sociability rose sharply before clinical relapse, allowing prediction of relapse with **89% sensitivity and 75% specificity”

-** Digital phenotyping systems therefore set simple thresholds like “no calls/texts for 2 days” or “>50% drop in social interactions” as potential alerts for isolation and worsening negative symptoms (if weekly outgoing calls drop 30% below personal average, flag for review” or “if daily screen time >2× baseline, send an alert.— EMPOWER trial

• COMMUNICATION - “Trigger alerts when SD deviation occurs” | 1. Again, reduce location = increase negative symptoms

2. Reduced calls/messages = relapsing

3. Changes in data trend compare to 71% of past data point to higher risk of relapse in the next 2 weeks? | **Sensor

4. GPS - movement

5. Sociability** | | Suicidal Ideation/Behavior | thoughts of suicide or suicide attempts (high risk across all serious mental illnesses)

Both – Critically monitored in clinical settings (SMI patients have a markedly elevated risk of suicide; up to half may attempt in their lifetime) . Also a major research and public health focus (risk factors and prevention). | Behavioral | ?? | | | | | Substance Use | alcohol or drug misuse co-occurring with mental illness (common across SMI)

Both – Assessed clinically due to its prevalence (e.g. ~50% of individuals with schizophrenia also have substance abuse) and studied in research as a factor that exacerbates outcomes. | Behavioral | NO sensor | | | | | Aggression/Agitation | aggressive behavior or extreme agitation (can accompany psychosis or mania in some cases)

Both – Managed clinically when present (e.g. agitation in psychiatric emergencies) and investigated in research (violence risk, often linked with untreated psychosis or substance use). | Behavioral | No Sensor | | | |

Quick and Dirty Cheat Sheets on DP Threshold

• Most research supports either (a) individualized change detection (deviation from a person’s own baseline), (b) model-derived risk scores that fuse multiple sensor streams, or (c) linking sensor anomalies to a clinically meaningful change on a validated scale (e.g., ≥4-point change on GAD measures).  • patients receiving alerts and timely support had a lower 12-month relapse rate (24% vs 46%) in one relapse-prevention study