Table 1

Baseline characteristics of the study population

General demographics	Development sample N=37 523		Validation sample N=15 649
General demographics	N	%	N	%
Age in years, median (IQR)*	32.2	21.4–48.9	32.5	21.4–49.1
Individuals under 16 years	2224	5.9	864	5.5
Sex, female*	20 561	54.8	8685	55.5
Substance misuse
Current or lifetime alcohol use disorder, excluding alcohol intoxication*	7257	19.3	3025	19.3
Current or lifetime drug use disorder (including drug intoxication)*	8384	22.3	3672	23.5
Alcohol intoxication at index	1416	3.8	815	5.2
Living status†
Living with other adults	14 151	37.7	5697	36.4
Living with children	15 493	41.3	6494	41.5
Treatment in the past 3 months
Any psychotropic medication	20 888	55.7	9537	60.9
Antidepressant treatment	12 527	33.4	6009	38.4
Antipsychotic treatment	4259	11.4	1834	11.7
Mood-stabiliser treatment	677	1.8	310	2.0
Physical health problems
New cancer diagnosis	411	1.1	149	1.0
History of self-harm
Method of index self-harm event‡
Any psychotropic medication overdose	1360	3.6	539	3.4
Cutting	4925	13.2	1614	10.3
Hanging, strangulation or suffocation	308	0.8	150	1.0
Drowning	51	0.1	23	0.2
Lifetime history of self-harm prior to index*	11 277	30.1	5372	34.3
History of self-harm in the past 12 months prior to index*	4281	11.4	1994	12.7
Number of lifetime prior self-harm episodes, including the index self-harm event
1–2 episodes	31 740	84.6	12 879	82.3
3+ episodes	5783	15.4	2770	17.7
Overnight admission	16 991	45.3	7531	48.1
Time between episodes ≤1 month	1929	5.1	838	5.4
Mental health in the past 12 months
Any psychiatric disorder (except substance use disorders)	16 472	43.9	7281	46.5
Serious psychiatric disorder	3006	8.0	1305	8.3
Criminal/violence/legal issues
Lifetime criminal record for any crime	13 451	35.9	5974	38.2
Criminal record for any crime in past 12 months	3816	10.2	1809	11.6
Lifetime arrest history for any crime	15 068	40.2	6506	41.6
Arrest history for any crime in past 12 months	6416	17.1	2818	18.0
Lifetime criminal record for violent crime	5729	15.3	2576	16.5
Criminal record for violent crime in past 12 months	897	2.4	416	2.7
Lifetime arrest history for violent crime	5402	14.4	2266	14.5
Arrest history for violent crime in the past 12 months	2141	5.7	872	5.6
Family history
Family history of suicide	1118	3.0	530	3.4
Family history of any psychiatric disorder	15 112	40.3	6503	41.6

Values are all numbers and percentages, except for age for which median years and IQR are reported. Criminal arrest refers to being charged for an offence.
*Core factor, kept in the final model independently of its statistical significance or predictive strength.
†Living status information was missing for 641 (2%) individuals in the development sample and 199 (1%) in the validation sample. Individuals under 16 years old with missing living status were reclassified as ‘living with other adults’ (2049 (92%) of the under 16s in the development sample; 815 (94%) in the validation sample). Of those with missing living status, two individuals died from suicide more than 12 months since index in the development sample, zero in the validation sample. For variables psychiatric treatment, mental health, family history, new cancer diagnosis and self-harm method, when there was no information, it was assumed to indicate the variable did not occur rather than a missing value.
‡It was possible for an individual’s index self-harm event to be coded under more than one of the methods listed. The majority of individuals not included in any of the listed categories had either non-psychotropic medicine overdose or an unspecified method of index self-harm. Drowning was too rare to enter into the multivariable model.