Limitations

One difficulty in assessing the quality of the many studies of the psychological health of military personnel and those working in similar occupational settings is that only a few had measured the time that each individual employee was deployed. Therefore, the results of this review are based on limited data. Also, a variety of psychological health measures were used in the reviewed studies, and these measures were often completed long after personnel had returned from their deployments. Additionally, the studies considered a range of different populations, making generalisation of these results problematic. For example, some studies included personnel from a single service (eg, Army),21–27 whereas others included personnel from all service branches (eg, Navy, Army, Marines and Air Force).14 ,20 Several studies included both regular and reserve forces,14 ,20 ,22 ,25 while others included only regular personnel.23 ,24 ,26 ,27 This may be particularly problematic, as previously it has been suggested that there are substantial differences in the health of deployed reservists in comparison with deployed regulars.1 Also, even though we were keen to examine the effects of ‘mismatch’ on health and well-being, only a few studies have examined this topic.

Another concern is that while some studies assumed that deployment length is, at least partially, a proxy for numerous in-theatre exposures associated with increased risk of subsequent health problems (such as seeing comrades killed or injured, incurring mortar or rocket fire), this assumption is crude at best. While it is true that the longer personnel are in theatre, the greater their risk of exposure to such events, it may well be that time away from home itself or the greater risk of adverse events occurring back home may also have affected mental health outcomes. Ursano et al 17 propose that in order to accurately assess the effects of deployment length, studies should focus on real-time assessments of traumatic events, loss of coping and efficacy of social support, taking account for how stressful each deployment is likely to be for personnel. However, the practicalities of adopting this approach would be extremely challenging, and to date there appear to have been no studies which have attempted this approach. The outcome of this review suggests, however, that the adverse effect of long deployments may be related not only to in-theatre events but also to home-front stressors, such as concern for family members and difficulty in maintaining family relationships.14 ,23 ,26

Effect on family, and marital stability

Extended deployment length is one of the principal causes of self-reported operational stress by personnel on deployment, and the source for this stress appears to be service members' concerns at being separated from their family.9 ,14 ,28 ,29 The reviewed studies suggest that there is a greater likelihood of marital and family problems (including an increased likelihood of spousal aggression) on return home for those troops who were deployed for the longest periods of time. This effect may be due to deployed military personnel having infrequent and irregular contact with family members, and thus having to deal with not only in-theatre difficulties but also the stress of missing key ‘home-front’ events such as children's birthdays, graduations and wedding anniversaries.28 Long deployments can lead to difficulties for the spouses of deployed personnel, as they may struggle financially and practically in caring for children and making family decisions. Such problems can lead to spouses having to reduce their working hours, or even take leave from or quit their jobs in order to care for the family,26 and longer periods of separation during deployments are associated with elevated rates of mental health problems for spouses themselves.24 A lack of support from their deployed partner can also lead to deterioration in children's behaviour at home and/or at school.26 In addition, long deployments can aggravate struggling interpersonal relationships, which may lead to an increased likelihood of infidelity, separation, divorce and difficulties ‘re-connecting’ with their children when personnel return home.28

To our knowledge, there are only two studies that have examined the effects of ‘mismatch’ on health and well-being. However, both of these studies reviewed herein suggest that the difficulties associated with longer deployment lengths may be particularly pronounced when there is a ‘mismatch’ between expected and actual length of time spent on deployment.26 This may be because tools which have helped families cope with the separation such as ‘count-down calendars’ (given to children so that they can keep a track of and be involved in their parent's return home) can be damaged. This might, in turn, lead to greater stress if the parent does not return on the previously stated date.28

Effect on physical, mental and social health

Studies of UK and US military personnel deployed to Iraq support the association between both longer deployment length and ‘mismatch,’ and a greater number of mental and physical health complaints among personnel.1 ,14 ,28 Of note, however, is that personnel who deployed within the UK Army's Land Harmony Guidelines showed no ill-effect related to deployment length, other than an increase in alcohol intake after returning home.14 This finding suggests that there may be a floor effect below which deployment length, in itself, is not a significant stressor. In this sense, the Harmony Guidelines appear to work when they are adhered to.

A contrasting view derives from a study on US peacekeepers deployed to the Balkans during 2002. This study led to the development of a theoretical model which predicted a linear increase in mental health problems with an increase in deployment length.22 Adler et al 22 propose that for mid-ranked, married, male soldiers, at 4 months into deployment there would be a 14.8% risk of their developing depression, at 6.5 months this risk would increase to 17.9%, and at 9 months this risk would be 21.6%.22 However, this model does not factor in the risk of developing depression on deployments longer than 9 months; nor does it give ORs or percentages for developing other mental health problems while on deployment. The model does, however, suggest that the longer average deployment length of US personnel serving in Iraq and Afghanistan, in comparison with their UK counterparts, may have contributed to the large differences in the prevalence of mental health problems (including PTSD) found in these populations in large cohort studies using the same measures of post-traumatic symptoms.1 ,16 ,30

Ideal length of deployment

Rona et al 14 found that, with the exception of alcohol misuse, there was a threshold for deployment length, beyond which UK military personnel begin to report significantly more psychological problems. The results of the studies reviewed here appear to place this threshold at approximately 6 months, or deploying for more than 12 months within the last 3 years.9 ,14 ,22 ,24 The one exception in the studies reviewed here is that Chaudhury et al 27 suggest this threshold is closer to 12 months rather than 6 months. However, given the cultural differences between the populations studied by Chaudhury et al 27 (the Indian military) and those studied by the other studies in this review (UK and US militaries), this finding may not be generalisable to ‘Western’ forces. Those serving in the Indian military as opposed to in the UK or US militaries are sent on deployment within or around their own country; they generally have a high level of support from the local population and, perhaps importantly, are able to keep in contact with their family more easily.27

Implications of deployment length and mismatch findings

The results of this review suggest that military personnel who spend prolonged periods away from home can suffer from cumulative stress, which may become especially evident when they return home. This finding supports the current practice of most Armed Forces, which acknowledge that periods of rest between deployments may allow personnel to ‘re-connect’ with family and friends and ‘re-adapt’ to home life. Having this period of rest may indeed reduce the risk of developing longer-term health problems.14 It is worth noting however, that to date, most studies and models examining the impact of deployments have been based solely on the study of male personnel; very few studies have examined the effects of long deployments separately for men and women. One study to do so found no effect of deployment length on the health and well-being of female personnel though a strong effect on the health and well-being of male personnel.22 However, another study found similar effects of deployment length on the attitudes towards alcohol in both men and women.23 Given the increasing number of women deployed in the military and their expanding roles in combat and combat support missions, the deployment experiences of female personnel need to be considered and studied more thoroughly before the full effects of deployment length and ‘mismatch’ can be generalised to the female military population.31

Applicability to other occupational settings

The majority of the studies included in this review have focused on all military service personnel, although few have looked specifically at members of the Air Force, and few have included both regulars and reservists. It is increasingly common for personnel from all branches of the military to work closely together on combat and training missions, and for reservists and National Guard members (in the USA) to deploy alongside regular military personnel. Furthermore, it is not only those in the Armed Forces that deploy to operational theatres. An estimated 126 000 security contractor staff have been deployed in Iraq since the beginning of combat operations in 2003, with a large number of national defence staff (civil-servants), journalists and other news media staff also working in operational theatres.4 ,7 ,8 ,27 The majority of non-military personnel working in theatre appear to be security contractors who themselves are most often former members of the Armed Forces.6 There may then be, some similarities between this subpopulation of personnel deployed alongside the Armed Forces and the deployed Armed Forces personnel themselves. Therefore, it may be important for security contractors to assess the effects of deployment length (and ‘mismatch’ if it occurs in these occupations, too) on the health and well-being of their employees.

The literature on the preparation of employees of non-military organisations for working abroad in what are likely to be challenging roles in stressful environments is sparse. However, much of this literature suggests that those who work away from their family for prolonged periods of time suffer from a higher proportion of mental, behavioural and social health problems compared with those who work in roles which allow them to see their family more often; subjectively, employees regard separation issues to be an important cause of occupational stress.32–37 These findings support the results of this review, which suggest that, although periods of deployment may differ greatly from those in military occupations, it may be useful for other organisations whose employees experience chronic occupational stressors and spend long periods away from home and/or from family to gain a clearer understanding of their long-term impact. Such organisations would include national foreign offices, non-governmental organisations, charities, field research organisations, news media organisations, oil companies, those in the fishing and seafaring industry, and mining and excavation companies. Such an understanding may help organisations better prepare themselves, their employees and their employees' families for these situations and, as a result, help to mitigate any subsequent health problems suffered as a result of these working conditions.22

Suggestions for further research

In order to better understand the effects of deployment length and ‘mismatch’ on health and well-being, future studies should (1) take an explicit measure of the time each individual has spent away from home, including tracking multiple deployments; (2) measure outcomes for both male and female personnel, and regular and reserve personnel, and assess these separately; (3) use prospective study designs so that causality can be assessed and to allow ‘mismatch’ to be measured thoroughly by recording expectations of deployment length (and analysis of how these expectations arise, what sources of information are used and so on) prior to the beginning of a deployment, as well as measuring the actual length of time an individual has spent away from home; (4) include relevant non-military personnel, such as private security contractors and NGOs.