-50 What data can be helpful for monitoring prison violence? • Capacity of the prison/number of prisoners, number of certain groups of inmates, number of staff and their responsibilities, staff-prisoner ratio, gender breakdown • Incident reports • Type of violence against staff by prisoners • Type of inter-prisoner violence • Incidents of self-harm and suicide • Use of control and restraint / use of force / solitary confinement • Escapes or attempted escapes • Deaths in custody • Reports of staff misconduct • Type and number of complaints • Contraband finds, specifying the type and amount • Number of prisoners accessing substitution drugs • Number/hours of prisoners with constructive activity (work, education, others) • Number of prisoners who spent 22 hours or more (alone) in their cells 4.2.2. Length of the visits The duration of a visit usually depends on the objectives set by the NPMs as well as on factors such as the size of the prison, knowledge about the place to be visited or if interpreters are needed to interview prisoners. In this context, NPMs should consider that monitoring violence might need more time than usual. Especially if NPMs want to monitor cultural issues, a visit of a couple of hours may not be sufficient. Moreover, prisoners might need some time before being willing to talk about staff-prisoner violence. Hence, in order to have sufficient time to gain a good understanding of all aspects relevant to violence, including those that are less visible, NPMs should consider conducting longer visits, at least three to four days. Some NPMs, such as the UK NPM (HMIP), have previously conduct visits of up to two weeks in one prison. 4.2.3. Composition of the visiting team The visiting team should ideally be composed of an interdisciplinary