Table 1:

Summary of studies included in the meta-analysis and the qualitative review, including study-specific definitions of subthreshold BP disorder and main findings of each study.

Author	Number of subjects	Sample	Type of study	Meta-Analysis Comparisons	Mean age* (years)	Percent Male*	Criteria for diagnosing SubBP	Main findings of study
Included in meta-analysis
Lewinsohn et al. 20028	SubBP N = 48; BP-I N = 17; Non mentally ill controls N = 307	Community	Longitudinal and cross-sectional	SubBP vs BP-I; SubBP vs Controls	16.6	46.8 (N=175)	One manic core symptom (DSM-IV criterion A) plus one or more other manic symptoms (DSM-IV criterion B).	Youth with BP-I and SubBP had more impaired functioning, and higher rates of psychiatric comorbidity and suicidality vs. controls.
Findling et al. 20059	SubBP N = 58; BP-I N = 65; Non-bipolar controls N = 44	Clinical	Cross-sectional	SubBP vs BP-I; SubBP vs Controls	11.3	53.9 (N=99)	Spontaneous, dysfunctional mood episodes that did not meet full criteria for any other mood disorder.	Youth with SubBP had greater impairment in functioning and more substantial mood symptomatology vs. controls.
Axelson et al. 200610	SubBP N = 153; BP-I N = 255	Clinical	Cross-sectional	SubBP vs BP-I	12.7	53.2 (N=217)	Elated mood plus 2 associated DSM-IV symptoms or irritable mood plus 3 DSM-IV associated symptoms, along with a change in level of functioning, for a minimum of 4 hours, and at least 4 cumulative lifetime days meeting the criteria.	No differences between SubBP and BP-I subjects on lifetime rates of comorbid diagnosis, suicidal ideation, or major depression.
Birmaher et al. 200911	SubBP N = 141; BP-I N = 244	Clinical	Longitudinal	SubBP vs BP-I	12.6	54.3 (N=209)	Elated mood plus 2 associated DSM-IV symptoms or irritable mood plus 3 DSM-IV associated symptoms, along with a change in level of functioning, for a minimum of 4 hours, and at least 4 cumulative lifetime days meeting the criteria.	Thirty eight percent of children with SubBP converted to BP-I or BP-II over the course of 4 years of follow up. SubBP was associated with less likelihood of full recovery following the index mood episode compared with BP-I and BP-II.
Demeter et al. 20135	SubBP N = 155; BP-I N = 290	Clinical	Cross-sectional	SubBP vs BP-I	10.5	63 (N=339)	Children and adolescents who met criteria for cyclothymia or Bipolar Disorder NOS as defined in DSM IV.	Subjects with BP-I had worse functioning and more severe symptoms of mania than subjects with SubBP.
Hafeman et al. 20136	SubBP N = 88; BP-I N = 71; Psychiatric Controls N = 545	Clinical	Cross-sectional	SubBP vs BP-I; SubBP vs Controls	9.4	67.8 (N=477)	Elated mood plus 2 associated DSM-IV symptoms or irritable mood plus 3 DSM-IV associated symptoms, along with a change in level of functioning, for a minimum of 4 hours, and at least 4 cumulative lifetime days meeting the criteria.	There were no differences in level of impairment or mood severity between SubBP and BP-I, but both groups had worse functioning, greater mood symptomatology, and a higher rate of conduct disorder compared to psychiatric controls.
Paaren et al. 20137	SubBP N = 50; Controls (negative screening for mania/ hypomania and depression) N = 229	Community	Longitudinal and cross-sectional	SubBP vs Controls	16.5	30 (N=27)	Youth who met criteria for one of the following: Brief-episode hypomania: criteria for hypomania were fulfilled but for less than 4 days; Subsyndromal hypomania: 1 or 2 main symptoms and 1–2 additional symptoms were fulfilled (total 3 or more symptoms), no specific duration defined.	Youth with hypomania spectrum illnesses had high rates of comorbid depression, had equal rates of suicidality when compared with subjects with MDD, and were more likely than controls to seek out mental health treatment. Fifty to sixty percent of youth with subthreshold hypomania continued to experience depressive episodes in adulthood but had low rates of conversion to BP-I (0 to 4%).
Not included in meta-analysis
Stringaris et al. 201012	SubBP N = 58 (based on parent report) and 48 (based on youth report)	Clinical and Community	Longitudinal	N/A	12.8 (parent report); 13.7 (youth report)	64 (parent report); 42 (youth report)	Youth with periods of elated or expansive mood, accompanied by at least 3 DSM-IV B criteria, the episode causes impairment and lasts more than 1 hour and less than 4 days. Could meet criteria based on parent report or youth report.	SubBP was associated with social impairment, DBDs and ADHD.
Zimmerman et al. 2000913	SubBP N = 202; BP-I N = 65; MDD N = 286; Controls N = 1273	Community	Longitudinal	N/A	19 (age range 14–24)	51.4 (N=1135)	Youth met criteria for MDD and either had 4+ days of elated/expansive mood without meeting DSM-IV criteria B, or had unusually irritable mood and 3 other manic symptoms, but symptoms were not observable by others.	SubBP was associated with family history of mania, higher rates of panic disorder and nicotine and alcohol use disorders, and higher rates of criminal acts when compared to MDD. SubBP also converted more often into BP-I at follow up.

SubBP = Subthreshold Bipolar disorder; BP-I = Bipolar Disorder type I; BP-II = Bipolar Disorder type II; DBDs = Disruptive Behavior Disorders; MDD = Major Depressive Disorder.

^*Mean age, percent male, and total number male are data listed for the entire study population of the paper.