Occupational Medicine 2007;57:92 97 Published online 2 November 2006 doi:10.1093/occmed/kql124 Occupational stress and strain in the naval service: 1999 and 2004 R. S. Bridger 1, S. Kilminster 1 and G. Slaven 2 Background Surveys of occupational stress were undertaken in 1999 and 2004. Objective To measure the prevalence of psychological strain and exposure to work-related stressors in personnel. Method A cross-sectional survey using a validated, reliable questionnaire was undertaken in 1999 and was replicated in 2004. The data were combined and models of stress strain were developed for male and female personnel in the Royal Navy (RN) and males in the Royal Marines (RM). Results The response rates were 78% in 1999 and 67% in 2004. Strain prevalence was 32% in 1999 and 33.5% in 2004. Strain rates were higher in females than in males and in personnel serving at sea. Reduced organizational commitment was associated with strain in males and females. Dissatisfaction with the physical work environment was associated with strain in RN females and RM. Role conflict was associated with strain in all groups. Work family conflict was associated with strain in males, but not in females. The models accounted for 20 30% of the variance in strain. Conclusion The strain rate in the Naval Service appeared to be similar to that in the other service occupations such as the UK Police, as did the sex difference in strain. The strain rate and stressor exposure ratings were remarkably stable over the period. Role conflict was found to be a generic stressor associated with strain. Key words Organizational commitment; physical work environment; role conflict; Royal Navy; strain; stress. Introduction In the late 1990s, the Naval Service (NS), consisting of the Royal Navy (RN) and the Royal Marines (RM), embarked upon a programme of research into occupational stress, led by G. Slaven. The programme was designed to support the development of health and safety policy. Between 1995 and 1999, 1516 NS personnel were medically downgraded prior to medical discharge but there was no evidence of high levels of anxiety and depression (hereafter strain ). Depression accounted for 2.2% and anxiety 0.7%. The NS has a low incidence of suicide lower than the British Army and Royal Air Force (RAF) and under half the rate of the equivalent UK male population (A. Shariff, G. Slaven, N. Pullinger, G. H. G. McMillan, unpublished MoD report). In contrast, chronic musculoskeletal disorders accounted for.45% of medical downgrades. Chronic knee and back pain accounted for 25% and 17%, respectively. Although 1 Institute of Naval Medicine, Crescent Road, Alverstoke PO12 2DL, UK. 2 DAPS (Science), HQ AG Command, Trenchard Lines, Upavon, Wiltshire SN9 6BE, UK. Correspondence to: R. S. Bridger, Institute of Naval Medicine, Crescent Road, Alverstoke PO12 2DL, UK. e-mail: hhfd@inm.mod.uk service at sea does expose personnel to physical risk factors for the latter disorders, the transition from pain to disability is known to be related to the presence of anxiety, depression and exposure to stress [1]. Adverse psychological reactions to occupational stress exposure may be reflected in a high incidence of other conditions. A workplace stressor is an aspect of the external work environment that makes demands of the individual that they feel cannot be met, causing strain [2]. Workload has been shown to be negatively related to job and workload satisfaction and positively related to depression, anxiety and irritation [3]. The NS has seen increasing work demands, reductions in manpower and societal and organizational changes have affected the service. The years 1999 2004 were marked by several major conflicts (e.g. in Afghanistan and Iraq) as well as extra work, such as the provision of cover during the firemen s strike. According to Karasek s [4] job demand control model, strain occurs when high job demands combine with low opportunity to influence tasks and procedures, resulting in poor employee health and low job satisfaction. There is considerable evidence to support the main effects predicted by the model for high work demands, skill discretion and decision latitude [5]. R. S. Bridger, Institute of Naval Medicine. Ó Crown Copyright 2006. Published with the permission of the Controller of Her Majesty s Stationery Office.
R. S. BRIDGER ET AL.: OCCUPATIONAL STRESS AND STRAIN IN NAVAL SERVICE 93 Karasek and Theorell [6] included social support as a stress buffer, predicting that employee strain would be highest when work demands are high with low levels of work control and social support [7]. Numerous studies have provided evidence for the protective effect of social support [8]. For example, higher psychosomatic health scores have been shown to be associated with high-strain jobs (high demands, low control) when social support was low [9]. Empirical studies have shown a consistent association between high levels of social support and reduced psychological strain [10 12]. The demands of life in the NS are many and there are a priori reasons to expect that personnel are exposed to many of the stressors identified in the literature. For example, personnel spend much of their time at sea, separated from their families, and working long hours. Life at sea places constraints on individuals that are different to, and in many ways greater than, those experienced in everyday life. This paper reports on the findings of surveys carried out in the NS in 1999 and 2004 to examine stressor exposures and their effects on personnel. Figure 1 depicts the assumed relationships between work stressors, strain and the role of buffers, such as social support. Methods Following Ministry of Defence ethics committee approval, cross-sectional surveys were carried out in 1999 and 2004 using the Work and Well-Being Questionnaire (WWBQ). The questionnaire contained a section dealing with demographic factors, such as rank, marital status, sex, branch/specialization, hours of work and whether the individual was serving at sea or ashore when the questionnaire was completed. A second section dealt with exposure to workplace stressors, scored using a five-point Likert scale (5 5 a negative affective response, 1 5 positive response, 3 5 neutral). Focus groups were conducted to identify the stressors. Six groups of five to eight individuals of equivalent rank in three different establishments LONG HOURS ROLE CONFLICT LACK OF RESOURCES PHYSICAL WORK ENVIRONMENT WORK/FAMILY CONFLICT AUTONOMY AND CONTROL PEER SUPPORT SUPERVISOR SUPPORT ORGANIZATIONAL SUPPORT DOMESTIC SUPPORT STRAIN (GHQ12 score >=4) Stressors Buffers Outcome Figure 1. Potential relationships between work stressors, buffers and strain. participated. A pilot questionnaire was then circulated to 600 randomly selected personnel. The returns were factor analysed and only items that loaded discretely and separately onto specific factors were selected. The item set was reduced by calculating alpha coefficients for each of the scales and removing items until the value of alpha exceeded 0.7, yielding a final questionnaire with 11 stressor scales [13]. A third section of the questionnaire contained the GHQ-12 to measure strain [14]. The final section provided space for open-ended comments. The sampling rate was 4.2% for males and 20% for females (the latter to ensure adequate sub-sample size for analysis). The sample was stratified by branch. The total numbers of males and females in December 1998 were 40 400 and 3300, respectively. The sample sizes for the main survey were chosen such that the maximum errors on unknown percentages indicating X (e.g. strain case ) were 1.5% for males and 2.5% for females. Assuming a response rate of 65 70%, the sample sizes were calculated at 1600 males and 600 females. Questionnaires were posted to 2194 randomly selected personnel in 1999 and to 2672 randomly selected personnel in 2004. All data were initially entered into MS Excel. Data were validated by double data entry cross-validation in addition to outlier and range checks. Subsequently, all data were analysed by Statistica v6 (Tulsa, OK, USA). For the main independent variables from the WWBQ, we computed 1 week test retest reliability (n 5 15) on the sub-scales and summary scores with Pearson product moment correlations. In addition, we carried oblique and orthogonal varimax factor analyses, confirming the factor structure previously given by the main author of the WWBQ. The various factors from the WWBQ were compared as outcome measures between year (1999 versus 2004), gender, rank and by RN or RM and listed as descriptive statistics and in some cases as t-tests. Stress cases were presented as percentages and 95% confidence intervals (CIs) and broken down into relevant sub-samples, e.g. RN versus RM. Forward stepwise regression procedures were carried out by regressing GHQ as either a continuous variable on the WWBQ predictors or as a stress case by dichotomous discriminant function analyses and confirmatory logistic regression. Residual plots were examined. Only models with significant predictors are reported. Results The GHQ-12 had a test retest Pearson correlation of 0.60 for the raw score with no difference in the number of cases on Monday and on Friday when a cut off score of $4 was used. Thus, strain rates were calculated using a cut off score of $4. All demographic factors had correlation coefficients of 0.99 1.00 and all stressors scales had coefficients.0.60 (P, 0.05).
94 OCCUPATIONAL MEDICINE The response rates were 78% in 1999 and 67% in 2004 all were.50% for both officers and ratings and for males and females. The mean age was 31.05 years (SD 7.63) in 1999 and 31.90 years (SD 8.06) years in 2004. Mean length of service was 12.27 years in 1999 (SD 8.06) and 12.69 years in 2004 (SD 8.54). No differences in age and length of service were statistically significant (P. 0.05). The mean GHQ-12 scores in 1999 and 2004 were 2.84 (SD 3.11) and 2.86 (SD 3.18). The difference in scores was not statistically significant (P. 0.05). The median score was 2, on both occasions. The GHQ-12 scores for the 1999 and 2004 surveys were converted to strain rates on a case/non-case basis using a cut off score of $4. The rates were 32% in 1999 and 33.5% in 2004 with no statistically significant difference between them (P. 0.05). Strain was more prevalent among females (P, 0.05) than among males, with no statistically significant differences between 1999 and 2004 (P. 0.05, see Table 1). Male ratings had higher strain rates than male officers in both surveys (P, 0.05, Table 2) but rank did not appear to differentiate strain in females (P. 0.05). Female ratings had higher strain rates than male officers of any rank (P, 0.05). The overlapping 95% CIs of the 1999 Table 1. Prevalence rates of strain in NS males and females in 1999 and 2004 No. of respondents Strain rate 95% CI 1999 2004 1999 2004 1999 2004 Males 1217 1319 31 31 28 34 28 33 Females 490 430 43 41 38 47 36 45 All 1707 1749 32 34 29 34 31 36 Strain rate refers to the percentage of respondents scoring $4 on the GHQ-12. Table 2. Strain rates by rank and sex in 1999 and 2004 No. of respondents Strain rate a 95% CI 1999 2004 1999 2004 1999 2004 RN male officer 251 291 24 25 19 30 20 30 RN male rate 801 825 34 34 31 37 31 37 RM officer 26 48 19 15 7 39 5 25 RM other ranks 134 155 29 30 21 36 23 37 RN female officer 75 98 33 39 23 45 29 48 RN female rate 412 332 44 42 39 49 37 48 Strain rate refers to the percentage of respondents scoring $4 on the GHQ-12. Other Ranks and Rate in the left-hand column refer to sailors and marines below the rank of officer. Totals for 1999 5 1699 (Table 2) versus 1707 (Table 1) is due to data censoring, i.e. missing data. There was no censoring for the specific fields 2004 in Table 1 versus Table 2. Totals were 1749. and 2004 strain rates indicate no statistically significant difference between the groups (P. 0.05). The chi-squared test was used to investigate the proportions of strain cases among personnel serving at sea or serving ashore when the questionnaire was completed. Separate analyses were carried out for males and for females at both time points. In all cases, a larger proportion of personnel were experiencing strain when serving at sea than ashore (chi-squared 5 9.54, P 5 0.002, and 10.79, P 5 0.001, for males in 1999 and 2004, respectively, and 12.39, P 5 0.0004, and 6.76, P 5 0.009, for females in 1999 and 2004). Service at sea was therefore deemed to be associated with strain (Table 3). The stressor item scores were summed and the means and standard deviations were calculated (Table 4). The mean stressor rankings for 1999 and 2004 were compared using the t-test. Statistically significant differences in mean scores were found for autonomy and control, organizational commitment and organizational support. However, these differences were small (0.1 0.2 of a point on the five-point scale and unlikely to be of any psychological significance). Support from leaders, peers and family was rated positively, as was organizational commitment. Autonomy and control and role conflict were rated neutral. Lack of resources, work family conflict and organizational support were rated negatively, on average. The lack of significant differences in strain rates and stressor scores in the two surveys enabled the 1999 and 2004 data sets to be combined and subjected to multiple regression analysis. Separate regression analyses were carried out for RN males, RN females and RMs. Table 5 presents the main findings. The stressor most strongly associated with strain in RN males was role conflict. Lack of leader support and low organizational commitment were also associated, indicative of a buffering effect. The multiple correlation coefficient had a value of 0.49. The square of the multiple correlation coefficient gives the proportion of variance in strain accounted for by these stressors. A coefficient Table 3. Association between serving at sea and serving ashore and strain prevalence in males and females Males Females Sea Shore Sea Shore 1999 Strain 37 (142) 28 (168) 57 (61) 37 (128) No strain 63 (241) 72 (438) 43 (47) 63 (215) 2004 Strain 38 (149) 28 (190) 52 (58) 38 (104) No strain 62 (248) 72 (491) 48 (53) 62 (171) Table shows the percentages (and frequencies) of RN personnel serving at sea and serving ashore, with and without strain in 1999 and 2004.
R. S. BRIDGER ET AL.: OCCUPATIONAL STRESS AND STRAIN IN NAVAL SERVICE 95 Table 4. Comparison of WWBQ stressor scale scores in 1999 and 2004 Stressor Mean 1999 Mean 2004 t value SD 1999 SD 2004 Interpretation Leader support 2.2 2.3 0.3 1.0 0.9 Positive Peer support 2.5 2.5 ÿ0.4 0.9 0.8 Domestic support 2.7 2.5 0.5 1.0 1.0 Organizational commitment 2.8 2.7 ÿ5.0* 0.8 0.8 Autonomy and control 3.0 2.9 ÿ3.3* 1.2 1.1 Neutral Role conflict 3.1 3.1 ÿ1.3 1.1 1.1 Resources 3.4 3.4 ÿ0.3 0.8 0.8 Work family conflict 3.5 3.5 ÿ1.8 0.9 0.9 Physical work environment 2.0 1.9 ÿ0.8 0.8 0.8 Organizational support family/personal problems 3.7 3.5 ÿ5.5* 0.9 0.9 Negative Organizational support work problems 3.9 3.7 ÿ5.7* 0.7 0.8 Means and standard deviations summed over all respondents. *P, 0.01. Table 5. Multiple regression models with GHQ-12 score as the dependent variable versus demographic and psychosocial predictor variables for RN males, RN females and RM Regression coefficient Correlation coefficient RN males a Leader support 0.12 0.31 Work family conflict 0.12 0.31 Organizational commitment 0.11 0.31 Role conflict 0.14 0.30 Peer support 0.10 0.26 Domestic support 0.06 0.04 Autonomy and control 0.08 0.23 Organizational 0.06 ÿ0.02 support family problems Resources 0.05 0.21 RN females b Role conflict 0.13 0.30 Organizational commitment 0.18 0.27 Physical work environment 0.16 0.25 Leader support 0.09 0.24 Autonomy and control 0.10 0.21 Resources 0.09 0.11 RM c Role conflict 0.29 0.40 Work family conflict 0.18 0.33 Peer support 0.15 0.27 Physical work environment 0.14 0.32 a Dependent variable GHQ total, multiple R 5 0.49, R 2 5 0.24, F 5 47.17, df 5 11,1677 and P, 0.001. b Dependent variable GHQ total, multiple R 5 0.43, R 2 5 0.18, F 5 15.95, df 5 7500 and P, 0.001. c Dependent variable GHQ total, multiple R 5 0.51; R 2 5 0.26; F 5 19.6; df 5 4, 4225 and P, 0.001. of 0.49 indicates that the variation in exposure to these stressors accounts for almost 25% of the variance in strain as measured by the GHQ-12. Role conflict was the most important predictor of strain in the RM, followed by poor physical work environment. Low peer support was associated with strain, indicative of a buffering effect when support is good. The predictor variables accounted for 26% of the GHQ-12 variance. Dissatisfaction with the physical environment and role conflict were the main work stressors associated with strain in RN females. Organizational commitment appeared to have a buffering effect. The model accounted for 18% of the GHQ-12 variance. Discussion The main findings of the 1999 survey were replicated in 2004. Despite increased workload and, for some, exposure to several major global conflicts, strain rate did not change between 1999 and 2004 and was higher than the general population rates of 15% of males and 19% of females [15]. Strain was more prevalent among females than males, irrespective of rank or age. This accords with the findings of studies of similar occupational groups [16] such as the UK police force, where the strain rate was strikingly similar to that in the NS, as was the difference in strain rate between males and females [17]. Ratings of stressor severity changed little over the time period. Leader support, peer support, domestic support and organizational commitment were rated positively but were associated with strain, indicating that below-average leadership or a lack of commitment leads to strain. The assertion that a naval career demands high organizational commitment comes from a survey of naval personnel on a Greek warship [18]. The male-only ship s company had a strain rate of 48.8%. The strain prevalence rate of officers was 25.5% (comparable to 25% in RN male officers). Among ratings (non-officers), who were conscripts, the rate was 88%. Although organizational commitment was not measured in this study, it is likely that it was lacking in conscripts.
96 OCCUPATIONAL MEDICINE Role conflict and autonomy and control were rated as neutral. Role conflict is likely to be related to excessive workload (e.g. when occupying different work roles simultaneously) and was associated with strain across the NS. Hours worked per week were not associated with strain but long hours may reflect the need to occupy several work roles. Availability of resources, physical work environment and organizational support for work and family problems were rated negatively. Only physical work environment was associated with strain, however, and only for RN females and the RM. Additive models, in which the risk of strain increased with the number of stressors to which an individual is exposed (Table 5), provide some support for the stress strain model in Figure 1. For RN males, work family conflict and role conflict were the main work stressors associated with strain. More than 50% of RN males were married. Supporting evidence for the assertion that separation from family is associated with strain comes from Limbert [19] who found a strain rate of 32% (GHQ-12) in a group of RN, RAF and Army personnel serving in the Falkland Islands and not accompanied by their spouses. Commitment to the organization, support of leaders and peer support appeared to have a buffering effect. For RN females, role conflict, the physical work environment and a lack of autonomy and control were the main work stressors associated with strain. Organizational commitment had a buffering effect. Only 16% of RN females were married and it is plausible that females are more likely to leave the NS after marriage to avoid work family conflict. For the RM, role conflict, work family conflict and the poor physical work environment were associated with strain, with peer support having a buffering effect. Service at sea is one of the features that most distinguishes a naval career from that in other uniformed services and it is somewhat surprising that strain rates were higher among those at sea. However, naval life exposes personnel to role conflict, a poor physical work environment and work family conflict and demands commitment to the NS. These exposures are usually greater when personnel are serving at sea. Commitment to the organization and support from leaders and peers has a buffering effect that protects individuals from strain. Initiatives currently being implemented to reduce strain are consistent with the model in Figure 1. The physical work environment on ships is poor due to exposure to ship motion and extreme weather. Accommodation is spartan cramped and with only basic facilities. Accommodation is being improved gradually and improved habitability on new ships is a requirement of the procurement process. 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