The labour force participation of women in Switzerland has increased steadily, and is now one of the highest in Europe. In 1970, only 49% of all women in Switzerland aged 15 to 64 years were engaged in paid work, as opposed to 75% in 2007. For women aged 25 to 45 years with at least one pre-primary school-age child, the participation rate increased from 40% (1990) to 62% (2000) in a single decade. As a result, the number of working women (and men) with childcare and/or other private responsibilities and family obligations (e.g., elder care) is growing rapidly in Switzerland as in most other industrialised nations [1].

This cross-national trend has generated much scientific attention to the issue of reconciling work with private life under the rubric of work-family conflict (WFC) and a considerable body of research literature on the subject matter. Role conflicts between work and family life occur "when demands of participation in one domain are incompatible with demands of participation in the other domain" (p. 411) [2] or "when one's efforts to fulfil work role demands interfere with one's ability to fulfil family demands and vice versa" (p. 888) [3]. Researchers commonly distinguish between three forms of WFC (time-based, strain-based, and behaviour-based) [4, 5] in two causal directions (work-to-family and family-to-work) [6–8]. However, most studies focus on time-based and strain-based work-to-family conflict.

Amidst a rapidly growing number of research studies on this topic, a new research tradition has developed centered on examining the causes and health- or work-related effects of WFC [9–14]. This literature has also enriched established research domains such as work-related health and stress research, by introducing the WFC construct as a risk factor for health or an explanatory factor for work stress [15–17]. Various studies revealed a number of health-related effects of WFC. Mental and physical health-related outcomes included increased substance abuse (especially problem drinking), greater psychological stress, more frequent depression and other mental disorders, burnout, and other psychosomatic symptoms including lack of appetite, sleep disorders, headaches or fatigue [3, 15–24].

The research on WFC is commonly criticised for certain methodological and theoretical deficiencies [12, 14, 25–27]. Besides and partly in line with these qualified criticisms, the following limitations are addressed with the present study: First, the research has focused mostly on role conflicts between work and family. Thus, only a segment of the labour force is actually covered, namely those working men and women who have children or minors living at home. Singles, single parents, dual-income couples without children living at home, extended or patch-work families etc. are usually excluded from study populations in research on WFC.

Second, WFC research has been largely limited to certain subpopulations or professional categories--e.g., managers, self-employed, full-time workers, professors, teachers, students, dual-income couples, working parents/mothers--or certain settings--e.g., cities, schools, universities, public administration, hospitals, hotels, supermarkets. Mostly, the study populations are white-collar workers--i.e., well-educated members of the middle class employed by large companies. Unskilled employees and members of lower classes or ethnic/racial minorities have seldom been included in research efforts to date.

Third, most of the literature on WFC stems from English-speaking countries, in particular from North America. Due to differences in the work ethos, employment structures, and social norms related to work and family, the findings from North American studies cannot be transferred directly to the continental European context. To date, hardly any contributions from Switzerland and neighbouring countries with a scienticially sound basis have been published in this field.

In the present study, singles and childless dual career-couples are also included in the study population in order to overcome the traditionally limited scope of WFC research and its narrow focus on working men and women living with their own core families including dependent children. Hence, this study is focusing not only on role conflicts between work and family, but also considers role conflicts resulting from job demands that are difficult to bring in line with other role expectations and responsibilities in private life beyond family obligations. To document this broader scope and expanded study sample, we use the term "work-life conflict" (WLC).

Besides addressing the aforementioned shortcomings, the objectives or rather research interests of this study are:

• to analyse important work- and nonwork -related factors associated with WLC and to identify high prevalence groups in this regard;

• to study different mental and physical health correlates of WLC (as dependent variables); and

• to examine potential gender differences within these associations and between these correlates.

The following graph illustrates the research interests of the present study and at the same time specifies the work- and nonwork related factors and the health outcomes that are expected to be associated with WLC and therefore included in the investigation (see Figure 1).

The present study sought to answer explicit research questions about groups with elevated levels of WLC, important correlates and health-related outcomes of WLC among adult employees in Switzerland as well as potential gender differences in this regard.

Regarding the first research question about identifying groups at risk of experiencing WLC and work-related and other factors associated with WLC, the study clearly showed that high numbers of hours spent at work, regular overtime, long commutes and a high job status (management position) are all associated with elevated levels of WLC. These findings make sense, since high work demands compete with other social roles and private obligations for limited time, energy and psychological resources, thereby leading to multiple burden and increasing role conflict between work and private life [30–33]. Other significant and relevant influencing factors found in the present study were job insecurity and living with dependent children. Interestingly, a differentiated composite score for WLC composed of 2 items yielded more or less the same risk groups with above average prevalence rates as a dichotomous single-item measure (yes/no question) about one's difficulties in reconciling work with private life [28].

Nearly all of the above-mentioned results are fully in line with international research showing that high job involvement and workload and in particular a large time commitment to work as well as job insecurity and childcare responsibilities are antecedents of WFC [2, 7, 10, 20, 34]. On the other hand, three of the findings go against expectations and/or are not consistent with international WFC research. Firstly, contrary to international studies showing an association between flexible work schedules (such as flextime) and lower WFC [10, 34–36], in the present study variable work schedule in terms of alternating or changing working hours from day to day was found to be associated with higher WLC compared to fixed, constant working hours. Variable working hours in this sense may not represent real self-determined time flexibility at work, but poorly predictable and other-directed working hours which of course are not a resource for balancing or reconciling one's work with his/her private life.

Secondly, in international studies, job autonomy--also known as influence at work, decision latitude, operational flexibility or work-time control--was found to be related to positive spillover between work and family and to be protective with regard to WFC [31, 35, 37–39]. But in the present study, job autonomy was not significantly associated with WLC. This may be due to a measurement problem. Participation in decision-making at work as assessed in the SHP survey (see section on "Measures") may not imply real autonomy in how and when the job gets done and is therefore not beneficial for one's WLB.

Thirdly, housekeeping has also been shown to be another antecedent of WFC in international studies [20], but that finding was not replicated in the present study. Since the level of engagement in paid work varies depending on the time spent on housework in our study, more housekeeping hours per week often go along with lower level of employment and a decreased number of weekly work hours which have been proven to be beneficial with regard to WLB.

In spite of the oft-quoted dual burden of working women and despite the fact that women mostly spend more hours in combined work and family activities and have a greater total load than men [8, 40], in the present study women at large were found to be somewhat less affected by WLC than men, as reported in other studies [20, 41]. Every seventh man, but only every ninth woman in the study population showed a (very) high WLC. This finding is in line with gender role theory and perspective and the so-called domain salience hypothesis postulating that role pressures and conflict are itensified when either work or family roles are salient and central to the person's self-concept [5]. In other words: the more important a role is to an individual, the more time and energy that individual will invest in it and the more likely are conflicts with other roles [42]. In light of still persisting traditional gender roles [8] it is assumed that the work domain is a greater source of role pressures and conflict for men while the family domain is a greater source of role pressures and conflict for women [40, 43]. Based on this argumentation and according to the rational view of gender differences [8], it has been concluded that men report more work-to-family/life conflict than women and women report more family/life-to-work conflict than men [44].

But in fact, the gender difference found in this study and going in the assumed direction is caused by an under-representation of women in full-time jobs and management positions in the study population just as well as in the general (working) population. Only 34.2% of women in the study sample work full-time and just 21.1% are in a management position, whereas 86.9% of all men work full-time and 42.8% are in a leading position. If prevalence rates are adjusted for job status and level of employment--i.e., if women and men working full-time and in the same job position are compared (see Table 2) --the gender difference with respect to WLC decreases, disappears entirely or is even reversed.

Findings in the research literatur on WFC referring to gender differences are contradictory [44]. Some research has found no gender differences [40, 42, 45], whereas other studies have reported gender differences in this regard mostly in the sense and direction of women experiencing more WFC than men [8, 36].

Beyond this, some interesting gender differences were found. While in men regular overtime, variable work schedule, and high job status (executive or management position) were most strongly associated with a higher level of WLC, in women the time committed to work or rather the number of contracted hours spent at work was by far the strongest explanatory variable. Job insecurity, long commutes, and living with dependent children in contrast turned out to be additional factors of equal strength among both men and women. These findings need to be replicated by others before they can be generalised, since they are inconsistent with findings from other studies like Jansen et al.'s cohort study [20] that found job insecurity to be an antecedent of WFC especially for men, and overtime work, long commuting time and having dependent children to be greater risk factors for women than for men.

Altogether the variance explained by all explanatory and controlling variables included in the linear regression model was only 11.1% for men and 13.5% for women. This large 'unexplained variance' suggests that there are other relevant, but unconsidered factors especially in the nonwork domain such as family obligations beyond childcare, leisure activities not covered in the SHP, and personality traits or individual preferences concerning the need for WLB, work ethos, commitment to family etc.

As far as the second research question regarding health correlates of WLC is concerned, findings of the present study confirmed that WLC is quite strongly associated with impaired general well-being, reduced physical health and limited mental health. These findings concur with international studies. Allen and Armstrong [46], Grandey and Cropanzano [33] and Frone et al. [24] found that WFC was associated with poor physical health. Others showed that WFC had an adverse affect on mental health [19, 47] or was strongly related to depression [24], fatigue [20] and psychiatric disorders [3].

Results show reasonably strong associations with a clear gradient (odds ratios increase in tandem with WLC) almost throughout, and associations are not diminished when adjusting for age, education and different work and private life characteristics. Those men and women who report a moderate or (very) high WLC show almost consistently (although not always significantly) an increased relative risk for general ill-being and different mental and physical health problems (e.g., poor self-rated health, serious headaches, negative emotions and depression, sleep disorders, fatigue) in comparison with those with inexistent or very low WLC (reference group). Multiple adjusted odds ratios for the most exposed group with high or very high WLC range from 1.5 to 4.7 depending on the health outcome. Only sick leave or rather being absent from work for 20 days or more in the past 12 months constitutes an exception to this pattern and is not associated with WLC at all.

Interestingly, when looking at mental health problems as outcome variables, women show slightly higher odds ratios--i.e., somewhat stronger associations between WLC and mental health impairments--than men. This finding is supported by a previous longitudinal study of Kinnunen et al. [45] who found work-to-family conflict to be more detrimental to women's satisfaction and well-being than that of men. An explanation for this gender difference might be that negative spillover or interference from work to family/private life is more stressful and problematic mentally for women because the family role and private life domain is more important to the woman's self-concept and social identity [5, 8, 40]. Men in turn obtain their personal and social resources (e.g., self-esteem, social status, social identity, social support) more from work and are therefore less affected mentally by such role conflicts from work to family or private life and by negative sanctions as a result of noncompliance with family role demands [5, 8, 40]. So work-to-life conflict as measured in the present study may have more adverse effects on women's (mental) health and well-being, whereas life-to-work conflict which was not assessed in the study may impair men's health.

In conclusion, the results from the present study provide additional evidence for certain and basically changeable working conditions and private life situations as relevant factors associated with WLC and, most important, for different negative health outcomes as correlates of WLC. The findings complement findings from our own previous research [28] filling further the still existing research gap and lack of evidence in Switzerland referring to this. Concerning the main findings, the study results are largely consistent with the risk factors and health effects found in international studies and documented in the research literature on WFC. This could not be assumed since the present study differs significantly from most international studies on this topic with respect to the study population. We studied a large cross-section of the general working or rather employed population in Switzerland including childless singles or couples and blue-collar workers, whereas most international studies are based on small, specific and homogenous samples of 'middle class', white-collar workers excluding childless singles or couples a priori.

With more than 12% of the employed population of Switzerland being affected by relatively high or very high WLC and the high relative risk of poor self-rated health and various physical and mental health problems found among the "most exposed" group, it can be said that WLC or work-life imbalance is an issue of great importance and relevance for the public's health in Switzerland. WLC was clearly associated with both physical and mental health problems and general ill-being. To date and with the exception of very few studies (e.g. Fuss et al. [64] or Sandmark [65]), public health and social epidemiology, as one of its major scientific disciplines, have not taken up the issue of work-life conflict or (im)balance much less considered its role as potential health determinant. Research on health-related effects of WFC traditionally has been and remains a domain of (occupational) health psychologists. Hopefully, our findings will help place WLC on the research agenda of public health in the future.