Main findings

We found evidence to support both of our hypotheses. First, adolescents who were ideators or enactors differed significantly from the controls on the pre-motivational phase personality variables and motivational phase variables (i.e. socially prescribed perfectionism, self-esteem, brooding rumination and optimism). In addition, the ideators and enactors did not differ from each other on any of these measures. Second, it was the volitional phase variables (i.e. self-harm by family, self-harm by friends, descriptive norms and impulsivity) and the experience of negative life stress that distinguished the ideators from the enactors. Relative to ideators, those adolescents who acted on their thoughts of self-harm were significantly more likely to have a family member and/or close friend who had self-harmed, to believe that their

TABLE 2

Univariate multinomial logistic regression analyses (adjusting for clustering and controlling for age, mood and gender) of the association between self-harm status and volitional phase variables and negative life events ^a

Volitional phase variables and negative life events	Self-harm status	OR	95% CI	P
Self-harm in the family b
No self-harm behaviour or self-harm ideation	v. self-harm behaviour	7.27	5.84–9.05	0.0001
No self-harm behaviour or self-harm ideation	v. self-harm ideation	2.45	1.88–3.20	0.0001
Self-harm thoughts	v. self-harm behaviour	2.97	2.14–4.11	0.0001
Self-harm by friends c
No self-harm behaviour or self-harm ideation	v. self-harm behaviour	6.43	5.05–8.20	0.0001
No self-harm behaviour or self-harm ideation	v. self-harm ideation	2.76	2.23–3.41	0.0001
Self-harm thoughts	v. self-harm behaviour	2.33	1.75–3.12	0.0001
Descriptive norms (scale range: 0–28) d
No self-harm behaviour or self-harm ideation	v. self-harm behaviour	1.17	1.13–1.22	0.0001
No self-harm behaviour or self-harm ideation	v. self-harm ideation	1.11	1.06–1.16	0.0001
Self-harm thoughts	v. self-harm behaviour	1.06	1.03–1.09	0.0001
Impulsivity (scale range: 0–6) d
No self-harm behaviour or self-harm ideation	v. self-harm behaviour	1.29	1.20–1.38	0.0001
No self-harm behaviour or self-harm ideation	v. self-harm ideation	1.17	1.09–1.25	0.0001
Self-harm thoughts	v. self-harm behaviour	1.10	1.02–1.20	0.017
Negative life stress (scale range: 0–18) d
No self-harm behaviour or self-harm ideation	v. self-harm behaviour	1.49	1.43–1.57	0.0001
No self-harm behaviour or self-harm ideation	v. self-harm ideation	1.33	1.27–1.38	0.0001
Self-harm thoughts	v. self-harm behaviour	1.13	1.09–1.17	0.0001

a Each of the pair-wise comparisons that is significant remains significant after applying Holm's sequential Bonferroni correction method.

b Exposure to family self-harm (n) is 309/4201, 142/673, 295/626 in the no self-harm history, ideator and enactor groups, respectively.

c Exposure to friends’ self-harm (n) is 687/4207, 280/673, 404/623 in the no self-harm history, ideator and enactor groups, respectively.

d As these are dimensional/continuous measures, the odds ratio represents each one point increase in score.

friends/peers engaged in self-harm (descriptive norms) and they were significantly more impulsive. Our findings are not explained by mood or age variations across the groups nor can they be attributed to clustering within schools. Moreover, in the final multivariate analyses, we included all univariate predictors as explanatory variables (including age, gender, anxiety and depression), and neither index of mood entered the final model to distinguish enactors from ideators (although there was a non-significant trend for depression).

We have extended the findings of previous studies of self-harm in adolescents considerably by providing evidence for a priori hypotheses derived from a theoretical model that makes specific predictions about the types of factors that are associated with behavioural enaction of self-harm. ^{Reference Hawton, Rodham, Evans and Weatherall1,Reference McMahon, Reulbach, Corcoran, Keeley, Perry and Arensman9,Reference O'Connor, Rasmussen, Miles and Hawton11,Reference Hargus, Hawton and Rodham34} This is a significant advance as it moves beyond describing characteristics of self-harm phenomena to formulating inferential, theory-driven hypotheses about those factors that are associated with the development of self-harm thoughts v. those factors that facilitate the behavioural enaction of those thoughts. This is also the first study to

TABLE 3

Means (and 95% confidence intervals adjusting for clustering) by self-harm status controlling for age, mood and gender

	Mean (95% CI)
Variable	No self-harm behaviour or self-harm ideation	Self-harm thoughts	Self-harm behaviour
Pre-motivational and motivational phase variables
Socially prescribed perfectionism	18.50 (18.10–18.90)	21.61 (20.94–22.28)	22.25 (21.71–22.78)
Self-esteem	16.07 (15.97–16.18)	13.10 (12.82–13.38)	12.31 (12.06–12.55)
Brooding rumination	4.91 (4.71–5.11)	7.94 (7.65–8.22)	8.14 (7.82–8.47)
Optimism	19.71 (19.54–19.89)	17.32 (17.01–17.63)	16.84 (16.56–17.12)
Voltional phase variables and negative life stress
Self-harm by family a	0.07 (0.06–0.08)	0.21 (0.16–0.26)	0.47 (0.42–0.52)
Self-harm by friends a	0.16 (0.14–0.19)	0.42 (0.36–0.47)	0.65 (0.60–0.70)
Descriptive norms	4.55 (4.48–4.63)	5.29 (5.09–5.49)	6.18 (5.83–6.54)
Impulsivity	2.87 (2.81–2.93)	3.22 (3.06–3.38)	3.44 (3.26–3.62)
Negative life stress	4.04 (3.88–4.20)	6.66 (6.41–6.91)	7.92 (7.72–8.13)

a To be consistent, means are presented (0 = no self-harm by family/friends, 1 = self-harm by family/friends). A similar pattern emerges if the data are presented as frequencies.

demonstrate that motivational factors do not distinguish ideators from enactors, rather that volitional factors and the extent of life stress seem to govern behavioural enaction, determining when thoughts of self-harm are translated into acts of self-harm. Of the volitional factors, having family or friends who have self-harmed was statistically the most important. This is in keeping with the notion that contagion is an important influence on self-harm in adolescents. ^{Reference Hawton, Harriss and Rodham35} Although the rate of ideation is often reported to be higher than enaction in studies of this kind, ^{Reference Schotte and Clum14} the lower rate of ideation in the present study reflects the fact that our ideator group is comprised only of those adolescents who have reported serious ideation and never acted on such thoughts, i.e. they are an ideator-only group.

Strengths and limitations

Key strengths of the study include it being based on a theoretical model of self-harm/suicidal behaviour and it comprises a large representative community sample of adolescents. However, as the present study has demonstrated, only an association between volitional phase factors and retrospective thoughts and behaviours, a large-scale prospective study is required to determine the extent to which volitional moderators and negative life stress actually predict those individuals with thoughts of self-harm who go on to engage in self-harm. Also, the volitional factors included here are not exhaustive; future research is required before we can generate a more definitive list of volitional factors that govern behavioural enaction. We also relied on self-reported incidence of thoughts of self-harm and actual self-harm. Despite the large sample of adolescents included in the study, the vast majority of those who reported/thought about self-harm were female thereby precluding reliable group analyses by gender in the present study.

Implications

This study provides support for the tripartite IMV model of self-harm/suicidal behaviour. It also helps establish self-harm as a ‘health’ behaviour, not just a sign of clinical disorder. Consequently, future research should examine the extent to which self-harm is amenable to established behaviour change techniques ^{Reference Abraham and Michie36} as well as traditional therapeutic approaches. It also reinforces the view that we need to move beyond just psychiatric diagnosis to better understand self-destructive behaviours. ^{Reference O'Connor, O'Connor, Platt and Gordon12,Reference Van Heeringen and van Heeringen37} It is also worth highlighting that the large sample size cannot account for the statistically significant differences between ideators and enactors on the univariate volitional phase variables. If these differences were statistical artefacts, one would expect to find similar differences among the pre-motivational phase personality and motivational phase variables. No such differences were evident. The implications for clinical practice and prevention are also considerable.

First, the present findings suggest that it may be important in therapy to use psychosocial interventions that differentially address the pre-motivational/motivational and the volitional phases of self-harm. For example, a cognitive-behavioural intervention could address some of the underlying processes that contribute to the development of thoughts of self-harm. ^{Reference Wenzel, Brown and Beck38} These may include tackling perfectionistic beliefs or brooding rumination. In addition, a behaviour change-based intervention may be used to address the effect of exposure to self-harm on behavioural enaction. ^{Reference Abraham and Michie36,Reference Dixon and Johnston39} From a public health perspective one might consider interventions to try to modify adolescent norms associated with self-harm.

Second, these findings also provide guidance on the types of questions and issues that clinicians may wish to address if a young person discloses having thoughts of self-harm. Asking about exposure to self-harm by others could be beneficial, as could a closer inspection of the individual's propensity to be impulsive.

Given the apparent role of so-called exposure or social learning variables (i.e. self-harm of others) in the aetiology of self-harm enaction, future research should investigate potential mechanisms to explain how they bridge the self-harm thoughts-behaviour gap. In another component of the present study, we obtained some evidence for social learning and legitimisation of self-harm explanations (such as an adolescent saying ‘if it is okay for my mother to self-harm when she is under pressure, it is okay for me to do so as well’). ^{Reference O'Connor, Fraser, Whyte, MacHale and Masterton22} Using data from the CASE study in England, Hargus et al ^{Reference Hargus, Hawton and Rodham34} found that adolescents who explained their self-harm in terms of being suicidal were more likely to have family members who had died by suicide than those who explained their self-harm in other ways, who were more likely to have friends who had self-harmed. Thus, the context and nature of the exposure to others who have self-harmed may be important. We also need to determine the role of such factors in repeat self-harm v. single-episode self-harm as well as among those expressing suicidal intent v. those who do not.