Estimation of the real population and its impact on the utilisation of healthcare services in Mediterranean resort regions: an ecological study

Background The demographic structure has a significant influence on the use of healthcare services, as does the size of the population denominators. Very few studies have been published on methods for estimating the real population such as tourist resorts. The lack of information about these problems means there is a corresponding lack of information about the behaviour of populational denominators (the floating population or tourist load) and the effect of this on the use of healthcare services. The objectives of the study were: a) To determine the Municipal Solid Waste (MSW) ratio, per person per day, among populations of known size; b) to estimate, by means of this ratio, the real population in an area where tourist numbers are very significant; and c) to determine the impact on the utilisation of hospital emergency healthcare services of the registered population, in comparison to the non-resident population, in two areas where tourist numbers are very significant. Methods An ecological study design was employed. We analysed the Healthcare Districts of the Costa del Sol and the island of Menorca. Both are Spanish territories in the Mediterranean region. Results In the two areas analysed, the correlation coefficient between the MSW ratio and admissions to hospital emergency departments exceeded 0.9, with p < 0.001. On the basis of MSW generation ratios, obtained for a control zone and also measured in neighbouring countries, we estimated the real population. For the summer months, when tourist activity is greatest and demand for emergency healthcare at hospitals is highest, this value was found to be double that of the registered population. Conclusion The MSW indicator, which is both ecological and indirect, can be used to estimate the real population in areas where population levels vary significantly during the year. This parameter is of interest in planning and dimensioning the provision of healthcare services.


Background
The demographic structure has a significant influence on the use of healthcare services, as does the size of the population denominators [1]. However, the vast majority of the studies published on the issue concentrate on factors referring to permanent populations. In areas such as tourist resorts, where large structural changes and annual fluctuations occur, the biggest problem lies in estimating the size of the population, before going on to consider its structure.
In the final decades of the 20th century, the coastal areas of developed countries in temperate climate zones advanced dramatically in both social and economic terms. In 1994, it was estimated that two thirds of the world's population lived within 150 km of the coast, and this value was expected to increase to three quarters by the year 2025 [2]. Beyond all doubt, current levels of economic globalisation have favoured the increased mobility of populations [3].
In Europe, the clearest manifestation of coastal development is to be found along the Mediterranean shores from Spain to Greece, a space in which an authentic urban continuum has been created everywhere physically possible [4]. In addition to concentration in terms of land occupation, tourism also presents a high degree of variability in time, with a marked increase in activity during the summer months; this fact heightens the impact on the environment and tends to produce a model that is economically fragile.
Very few studies have been published on methods for estimating the real population [5]. The earliest studies of the mobility of patients within developed countries highlighted disparities in health-influencing factors, among both the host and the incoming populations, together with variability in the treatment offered to the latter and increasing concern among their respective governments about healthcare costs [6][7][8]. The lack of information about these problems means there is a corresponding lack of information about the behaviour of populational denominators (the floating population or tourist load) and the effect of this on the use of healthcare services, leading to the seriously inadequate planning of healthcare resources. Indeed, this fact has been reported as impeding the estimation of rates of morbidity-mortality [9][10][11][12].
The goals of the present study are: a) To determine the real population in a popular tourist area; and b) to evaluate the impact on the utilisation of hospital emergency services by the permanent, registered population and by that of non-residents, in two popular tourist areas.  [14]. In estimating the Kg. of MSW generated per inhabitant per day in the CSHD, the Control Zone (CZ) was taken as all the inland municipalities in the province of Malaga (thus excluding the coastal municipalities, the city of Malaga and a nearby dormitory town); for these areas, the demographic structure was assumed to be stable, presenting no significant changes throughout the year. In the case of Menorca, the direct estimator used was the variable known as Human Pressure (HP), this variable being applicable thanks to Menorca's island identity, and to the fact that all entries and exits of travellers, by sea or air, are recorded daily. Thus, the total population of the island, including the permanent and the 'floating' elements, is always known. The HP variable enables us to obtain the value of the Kg. of MSW generated per inhabitant per day for every month of the year, rather than having to use a single annual value.
An additional variable included was the maximum accommodation capacity, or the maximum number of beds available, estimated from the total recorded population plus the number of beds in registered accommodation facilities plus the number of second homes and unoccupied residential buildings (corrected by a factor of 10% to allow for speculative housing, this being defined as the flats and houses sold within a year of their purchase) multiplied by the mean number of occupants (3.1) [15].
Statistical Analysis: The ratios calculated were applied to the production of MSW in the two study areas in order to estimate the tourist load and its range; a statistical description was achieved by means of measures of central trend and of dispersion. We estimated the Pearson correlation coefficient (after testing for normality with the Kol-mogorov-Smirnov test), the coefficient of determination and the 95% confidence intervals for the estimates of the real population and the use of hospital emergency services during the year in which the study was carried out. For Menorca, these values were calculated for the relation between the MSW ratios and HP. The impact on the demand for healthcare services is described by the relative distribution of patients treated by hospital emergency services and by the patients' mean age, calculated monthly, the patients being differentiated by their place of residence within the reference healthcare district. The healthcare utilisation rate was calculated from the estimated real population (assuming a MSW production of 1.4 Kg. per inhabitant per day). The level of significance was taken as p < 0.05.

Results
The ratio of Kg. of MSW produced per registered inhabitant per day varied between 2.45 for the CSHD and 1.23 for the CZ. When the real population of the CSHD was estimated, based on three different ratios for the generation of MSW per inhabitant (1.2, 1.4 and 1.6 Kg./person/ day), the real population thus estimated exceeded the official values in every case. The estimated monthly population ranged from the 341,000 inhabitants calculated for the month of February, with a ratio of 1.6, to a maximum of 743,000 inhabitants in August, calculated using a MSW ratio of 1.2. The number of estimated inhabitants did not exceed the maximum accommodation capacity except the value calculated for the summer period with a MSW ratio of 1.2. (Table 1) Similar results were obtained for the estimated real population of Menorca using the HP parameter; during May-October, this value was double that of the official figure, while for the remaining months of the year the official value and the HP estimate coincided. The population level was minimum in January, with 70,000 inhabitants, and maximum in August with 177,000. During the months of January to March and in November and December, the estimated real population was less than the official recorded value.
The correlation coefficient between MSW and HP in Menorca was 0.99 ( Table 2). The MSW/HP ratios obtained ranged between 1.38 Kg./person/day in December and 1.55 Kg./person/day in January. In both Menorca and the CSHD, the degree of correlation between the MSW and the monthly number of cases treated at the emergency department of the hospital in the study areas exceeded 0.90 (p < 0.001).
With respect to the impact on health care services, the unregistered population constituted up to 34.9% of all urgent admissions during the month of August in the Costa del Sol Health District, and up to 26.1% in Menorca in the same period. The mean age of non-residents decreased during the summer months in both areas, in comparison with that of the resident population, for whom the corresponding values remained stable (Table  3).

Discussion
The production of MSW and the population estimates based on this parameter are positively related to the utilisation of emergency healthcare services at hospitals in two geographic areas where tourist activity is significant. The frequency of use of hospital emergency service facilities varies during the year, as does the user profile.
Prior to obtaining the above correlations, we examined indirect indicators that might be used to establish the real population, such as the consumption of electricity, water, cement or hydrocarbon fuels, or the intensity of road traffic, but only the generation of MSW correlated strongly with variations in population and with the use of emergency healthcare facilities.  [16], while in the coastal area of the same province this ratio was doubled. This phenomenon does not seem to be explained by a corresponding difference in income levels (in the province of Malaga, the weighted mean annual income in the CZ in 2002 exceeded 7,500 euros, while in the CSHD municipalities it exceeded 10,500 euros, only 40% higher). Nei-ther do we observe a systematic increase in the generation of MSW in different countries as income increases [17]. The ranges of ratios applied in this study are close to those measured in European Union countries in 2001, varying between 1.2 Kg./person/day (in Belgium, Portugal and Greece) and 1.6 Kg./person/day (in Germany, the United Kingdom and Holland). The mean value for the 25 countries of the EU is 1.4 Kg./person/day [18].
The estimates of real population based on the generation of MSW reveal a seasonal pattern: in the summer months, the estimated population doubles the official value. In the island of Menorca, seasonality is even greater, as in the first and fourth quarters of the year, the estimated and the officially recorded population values converge, while in the CSHD there exists an unrecorded population that remains stable during the winter months. This latter fact is consistent with the existence of different policies for tourism. On the island of Menorca, the traditional way of life, land and nature have not been displaced by mass tourism, while on the Costa del Sol there is a predominant service industry that is gradually becoming less seasonal by the integration of new areas of leisure activity.
Comparison of estimates of the real population with the utilisation of healthcare resources enables us to evaluate the consistency of these findings, as the greater the population to be attended, the greater the demand for healthcare. Nevertheless, it should be taken into account that the non-resident population normally suffers fewer health problems than the permanent population. The unrecorded population that is resident in winter is usually older, being mainly European pensioners. Among hospital activities, that of the emergency departments presents the highest degree of association with MSW production, The correlation coefficients between the number of emergency admissions and MSW production (exceeding 0.90) indicates a strong degree of association and explains the high percentage of variability in the use of emergency healthcare facilities. It should be stressed that the correlation coefficient was identical in the two study areas. This finding is consistent with the association found between MSW production and overnight stays at winter sports resorts in France [5].
The non-resident population of the Costa del Sol is basically made up of three groups: 1) European pensioners, especially from the United Kingdom, Germany and Scandinavia, who stay in the area for several months a year; 2) tourists, both from other areas of Spain and from many foreign countries, who visit the area mainly in summer, but also during other periods, taking advantage of the mild climate; and 3) the population living in neighbouring municipalities who work in the area, mainly in the catering and construction industries. Rates of utilisation of the emergency department at the Hospital Costa del Sol are stable throughout the year, both among the recorded and the unrecorded populations.
The European pensioners make a similar use of healthcare facilities to that of the permanent local population in the same age group, although many of them are not officially registered as resident in Spain. Thus there is an added demand for healthcare and other services (municipal services, infrastructure and communications), the funding for which is provided on the basis of the officially recorded population. The relative increase in the rate of utilisation of healthcare facilities during the months of greatest tourist activity (July and August), together with the fall in the mean age of patients attended, reflect the profile of a younger non-resident population with a higher level of open-air leisure activities, associated with a different morbidity profile. No analysis of healthcare facility utilisation is given for the island of Menorca because the estimation method was influenced by the seasonal economic cycle characterising the island (i.e., the fact that a greater population decrease occurs during the winter), which resulted in negative values being obtained for certain months.
The satisfactory results of the correlation analysis between MSW and HP underline the consistency of MSW as an indirect indicator of the real population, given the reliability of the HP variable in Menorca. This is of great importance, as in the case of the island no physical access is possible except that included in evaluating the HP variable.

Conclusion
Indicators such as the generation of MSW, which are ecological and indirect, are useful for estimating the total population in areas in which there occur significant changes during the year, if other types of indicators are not available. Annual variations in MSW generation are closely linked to the utilisation of healthcare services, and particularly of emergency hospital services. Such an estimation method is of interest for the planning and dimensioning of the supply of healthcare services, and could be used in other countries in the UE, given the availability of UE MSW data within the EUROSTAT system. Future studies are required to further investigate the structural characterisation of the tourist load and of the needs for healthcare services, broken down by age and sex, among other categories.