In this study we investigated the impact of demographic, socio-economic and need factors on the utilization of health services. The data showed that self-perceived health status -as a proxy measure of need- is the most important contributor to the utilization variance for three of the designated services (private physician, emergency departments and hospital admissions), a finding which is consistent with many previous studies [1–7]. Demographic variables such as age and gender were most strongly associated with visits to public (provided by health insurance funds) sector physicians. Socio-economic variables such as income and education did not have a statistically significant relationship with utilization, particularly in the case of secondary health services.
The results of the study seem to suggest the existence of equity in the use of primary health care services. Demographic and, to a lesser degree, need factors affected utilisation and no socio-economic gradient was apparent. Things were slightly different when the public and primary sectors were analysed separately, but once again inequity is not implied. Use of primary health services, provided by health insurance funds, was made according to demographic, socioeconomic and health care need variables. Women, elderly, less wealthy individuals and people with a lower physical health status visited their insurance fund physicians more. Demographic variables were the most important contributors and this may be explained by the fact that women reported higher consumption due to their increased awareness of health problems and symptoms when assessing their health status . Furthermore age is a factor inversely linked to health, therefore elderly -a high-risk group from the aspect of health status and economic welfare- seek more public primary services, which are free at the point of use.
Utilisation of private services was also affected by socio-demographic and need factors. Women, well educated and those once again of lower physical health status were more likely to visit private providers. It was expected that economic factors like income would affect utilisation of private physicians, which involves out of pocket payments. However, this was not confirmed by our study as opposed to an earlier study in Italy , where a linear relationship between the level of income and private utilization was observed. A possible explanation, in our case, is the underestimation of income. One third of the sample had not reported income. Even people who did may have underestimated it because the Greek population is often reluctant to answer these kinds of questions.
Another noteworthy fact is that the independent variables in the regression model (table 4) explain only a low portion of utilisation of private primary services. Besides the underestimation of income mentioned previously, another reason could be the small proportion of users having visited a private physician (14.0%), since the sample comprises an overall healthy population. An interesting topic for future research is the users' satisfaction from public primary services and if quality variations actually directed them towards private physicians. An important implication, which will be discussed subsequently, is that low-income individuals use primary private services as well.
Visits to hospital emergency departments and hospital admissions were related to health care needs, and no socio-economic factor characterized the use of those types of care. As reported in an earlier study, hospital utilization and the volume of inpatient services were significantly influenced by medical needs  or as Andersen  explains, hospital services received in response to serious problems and conditions would be primarily explained by need and demographic characteristics. The small amount of variance explained here implies the coexistence of other factors (e.g. lifestyle) that could affect the utilization of these health services, and this itself is another issue for future research.
Upon examining the number of visits, no socio-economic influence was revealed. The poorer and those with worse mental health visited more frequently physicians linked to their health insurance fund. Other studies [3, 4] have shown that people with higher education visited specialists more frequently or that they were more frequently referred to one. Socio-economic variations in the utilization of specialist services seem to be well-established in health systems in which referrals to specialists are made by primary physicians who play an important role in follow-up visits and hospital admissions. The structure of the Greek health system is different, primary health services concern mainly specialist services, which people choose freely without a referral.
Patients' preferences, awareness of their medical profile, availability of services and their expectations are important factors in seeking referred health care, mainly from specialists, in many European countries. Higher educated or wealthier individuals have different attitudes about the potential benefits, so they are more motivated to request specialist care . In the Greek health system there is no observed inequality in access or frequent use, but patients' expectations, awareness of their condition and educational level consist basic factors in tackling a health problem within a complex mixed public-private health system.
After studying the different use of public/private services (table 7), a pro-rich inequality was observed. This does not contradict what has been previously mentioned about the use of private services only (table 4), where the effect of income is not evident, most likely because the respondents are homogenous (i.e. users of private services). Contrarily, income is important when the combined (public/private) users are studied. People better off in respect to education and income levels were more likely to use private health services. Results from another study in Greece  reported that the two higher income groups spend approximately the same amount of money as the others combined. This inequality becomes more severe when low-income people are forced to use needed health services from the private sector (because of the incomplete network of public primary health services, long waiting lists, "under the table" payments and low quality of provided services) burdening their limited family budget.
Low-income individuals have greater health care needs expressed by lower physical and mental summary scores, and further supported by research in western European countries showing that morbidity and mortality risks are higher in lower socioeconomic groups . Although it seems that low-income individuals generally use health services, it is apparent that they are not exclusive users of the public services, but they are often forced to use private health services as well. This implies inequity in the distribution of care since the consumption of private health services is not limited to the higher incomes, but is extended to the lower ones as well, thus giving rise to issues of horizontal and vertical inequity. A possible explanation could be the inadequate public financing. Greece has the lowest percentage of public health expenditures among the EU countries. According to OECD data in 2002 , total health expenditures per capita were 1814$, of which public health expenditures per capita were only 960$. On the contrary, private expenditures are the highest among the EU countries, and this means that the income, in all socio-economic classes, is burdened for the use of health services.
Another possible explanation is the structural problems of the system. The large number of health insurance funds and the different range of health services they cover is the most typical characteristic in this case. More specifically, wealthier funds cover a large range of services, provide a better set of inpatient services or, in many instances, offer reimbursement when individuals purchase from private providers. Often, people insured by the most prosperous health insurance funds (approximately 10% of the insured population) are covered, to a large extent, for hospitalization in prestigious private hospitals, for all illnesses, specialized operations and examinations . This unequal distribution of provided health services, within the public sector, constitutes a structural weakness of the Greek health system, which the private sector exploits.
In spite of social insurance coverage of Greek citizens, the use of private services is extensive throughout the country. This could be attributed also to the absence of the "family doctor" in Greece, and the inability to select the desired physician in primary and secondary health care. The absence of the family doctor affects the delivery of care, access and the referrals to the health system. This results in patients accessing secondary care based on their own initiative. The adoption of a gate keeping system could result in a link between primary and secondary care, and an effective patient transfer. Moreover it could give emphasis to issues such as prevention and over-consumption (especially of hospital care), which pose a great burden on the health system . On the other hand, insurance funds covering people of low income are either incapable of fulfilling their needs, or they provide lower quality health care, in conjunction to long waiting lists, all of which affect the degree of satisfaction. Overall, a significant personal cost is created for the users, who are forced to turn to the private sector and spend a large part of their income. This implies that a more complete and satisfactory network of services could result in lower use of the private sector.
Finally, two limitations should be briefly underlined. First, this study concerned the broader Athens area, the capital of Greece, where medical personnel is more experienced and better equipped technologically, and consequently more specialised health services are available. The heterogeneous dispersion of resources in relation to the population throughout the country reflects an unequal availability of health services, which is expected to be more intense in rural areas. So the first restriction reflects lack of data on the pattern of use of the rural population. Another limitation, reported also in a study by Morris , was the fact that utilization measures were zero-one variables for four defined types of use and there was no information on the quality of provided services.