the most prominent european example is the european household panel which started in 1996 in the then 12 member countries . in 2003 the european statistics on income and living conditions ( eu - silc ) was based on the same sampling method . as far as we know , no published reports on the application of the household panels methodology for health surveys are available , despite the successful application of household panels in social research . the healthcare access panel ( hcap ) was developed primarily as a multi - purpose database with information about chronic diseases and healthcare utilization in germany . the sample should be large enough to contain sub - samples of persons with low prevalent diseases in sufficient numbers for special analyses . the follow - up of respondents with defined characteristics , e.g. symptoms or illnesses , should be possible . and the objective of this paper is to demonstrate the validity of results obtained with the healthcare access panel approach , as compared with results from other population - based data sources . this population panel is accessible any time at comparably low cost , it might be an alternative approach to expensive cross - sectional random sample surveys or longitudinal population studies designed for one objective upon time , at least under many circumstances . the existing national access panel of the tns infratest group in germany comprises a database with 73,100 households and 167,300 persons who agreed to participate in future surveys . in europe further household panels in italy , uk , spain , the netherlands and france with 221,300 households and in the us with 600,000 households exist within the tns research network . households are recruited for the healthcare access panel via different channels , e.g. address publishers , email - contacts or snowball - systems . the sample is evaluated continuously and underrepresented cells , e.g. defined by region or age - group , are complemented by quota recruitment . the panel members receive small incentives for their cooperation and the panel compliance is very high . beginning in 1999 ( healthcare access panel 1999 ; hcap 1999 ) and then following in 2002 ( hcap 2002 ) questions concerning the 12-month - prevalence of selected chronic diseases and healthcare utilization responses for up to five and in 2002 for up to four persons per household could be reported . the healthcare access panel 1999 comprises responses of 78,609 persons and 54,300 persons in 2002 . sociodemographic information about the respondent from the database could be combined with the healthcare data on an individual level . since all persons agreed to future participation , follow - up studies with persons suffering from special diseases can be done . the individual cases were given weight factors to optimize the sample structure with respect to age , sex and region . the next data collection for the healthcare access panel is planned for the year 2004 . since no bias - free population sample can be assumed a priori , comparisons with known , reliable population data are essential to demonstrate that the panel of volunteers could reflect the true population data in their distribution . the regional distribution of the healthcare access panel as compared with the data of the statistical yearbook of germany   is shown in table 2 ( tab . the distribution of the healthcare access panel matches the distribution of the german population in the administrative regions , as calculated by the federal agency for statistics , very well . 3 ) . as expected , the older age groups are somewhat underrepresented in the healthcare access panel , although frequent in absolute numbers . the following examples are to show whether and to what extent the evaluations of the healthcare access panel data lead to results that are comparable with population - based health data .   ( a ) hospital admissions rather extensive information is available from the national hospital discharge statistics , annually published by the german federal office for statistics . therefore comparable with the information from the healthcare access panel , which documented the number of hospital stays of the panel participants during the past twelve months . restricting the official population - based hospital discharge statistics to the age range up to 79 years ( as in the healthcare access panel ) , the resulting frequency per inhabitant is 0.17 - as found with the access panel ( tab . . this may be due to the fact that certain subgroups , which for example live in nursing homes , are included in population - based national statistics and are not included in the healthcare access panel . there is also a good congruence of the gender - specific rates of hospital discharge statistics and the rates estimated by the healthcare access panel ( data not shown ) . the comparability of the rates , determined by the healthcare access panel and by the official hospital discharge statistics , is similarly good across all german federal states ( tab . the maximal difference in the hospitalisation rate is 0.01 in 12 of the 16 administrative regions . somewhat more variation , but not alarming differences , can be seen in the four administrative regions with a small population size : hamburg , brandenburg , saxony , and thuringia . 1 ) shows a comparative evaluation of contacts with different outpatient physicians ,   i.e. the percentage of persons who had at least one out - patient consultation with the respective medical discipline . the data obtained with the hcap and those observed in the most recent german national health survey   were found to be very close , i.e. with some random oscillation . the most recent representative german national health survey ( gnhs ) was used again as reference . the figure shows that the frequency estimated by the hcap and the representative random sample survey is very close to each other , i.e. with the expected random oscillation . ( c ) prevalence of diseases in the population we compared the self - reported 12-month - prevalence of selected medical conditions between the healthcare access panel and the last nationwide representative random sample survey ( gnhs ) . the medical conditions had been assessed in the gnhs by trained physicians on the basis of structured personal interviews . even the age - specific distributions of hypertension and chronic bronchitis in the healthcare access panel are very good , compared to the correspondence of the german national health survey ( tab . there is no suspicion of a systematic difference among both data sources of disease prevalence . this reconfirms that the access sample is not materially biased if compared with a good - quality representative random sample survey of the same source population - at least for that kind of information . . just as often , however , will the results of analyses in the access panel be sufficient or even preferable concerning cost - effectiveness . advantages of the access panel approach might be :  the results can be obtained in a relatively short period of time ( a few weeks or months ) , at least as compared with a specific designed population - based survey . for a majority of social and health - related issues , matters of health services research or e.g. drug utilisation , the results of the access panel will be usually sufficient to give valid answers .  surveys of very large groups are possible if rare phenomena have to be studied . even for small sub - groups with specific characteristics sufficient numbers of participants will be available in most cases - which are often a problem difficult to overcome for planned population surveys due to the costs . the costs are considerably lower than for a planned cross - sectional random sample survey . even follow - up studies are possible : if certain information has been documented years ago , changes over time can be monitored ( historic cohort approach ) . comparisons among different countries are possible since access panels , using the same method , have been established in many countries of europe and in other continents . disadvantages can be :  the methodological design of the access panel can not be changed , although some helpful minor modifications can be discussed for individual situations . certain bias forms can be inherent in any self - selected cohort unless sufficient evidence for the contrary can be provided . real response rates can not be determined due to the self - selective nature of the panel . nonetheless , non - response rates of the panel members are important to know . the representativeness for the source population needs to be specifically discussed when results of the access panel should be generalized . however , this is also the case , to a lesser degree , for planned population - based random sample surveys . the regional distribution of the healthcare access panel as compared with the data of the statistical yearbook of germany   is shown in table 2 ( tab . the distribution of the healthcare access panel matches the distribution of the german population in the administrative regions , as calculated by the federal agency for statistics , very well . 3 ) . as expected , the older age groups are somewhat underrepresented in the healthcare access panel , although frequent in absolute numbers . the following examples are to show whether and to what extent the evaluations of the healthcare access panel data lead to results that are comparable with population - based health data .   ( a ) hospital admissions rather extensive information is available from the national hospital discharge statistics , annually published by the german federal office for statistics . therefore comparable with the information from the healthcare access panel , which documented the number of hospital stays of the panel participants during the past twelve months . restricting the official population - based hospital discharge statistics to the age range up to 79 years ( as in the healthcare access panel ) , the resulting frequency per inhabitant is 0.17 - as found with the access panel ( tab . . this may be due to the fact that certain subgroups , which for example live in nursing homes , are included in population - based national statistics and are not included in the healthcare access panel . there is also a good congruence of the gender - specific rates of hospital discharge statistics and the rates estimated by the healthcare access panel ( data not shown ) . the comparability of the rates , determined by the healthcare access panel and by the official hospital discharge statistics , is similarly good across all german federal states ( tab . the maximal difference in the hospitalisation rate is 0.01 in 12 of the 16 administrative regions . somewhat more variation , but not alarming differences , can be seen in the four administrative regions with a small population size : hamburg , brandenburg , saxony , and thuringia . 1 ) shows a comparative evaluation of contacts with different outpatient physicians ,   i.e. the percentage of persons who had at least one out - patient consultation with the respective medical discipline . the data obtained with the hcap and those observed in the most recent german national health survey   were found to be very close , i.e. with some random oscillation . the most recent representative german national health survey ( gnhs ) was used again as reference . the figure shows that the frequency estimated by the hcap and the representative random sample survey is very close to each other , i.e. with the expected random oscillation . ( c ) prevalence of diseases in the population we compared the self - reported 12-month - prevalence of selected medical conditions between the healthcare access panel and the last nationwide representative random sample survey ( gnhs ) . the medical conditions had been assessed in the gnhs by trained physicians on the basis of structured personal interviews . even the age - specific distributions of hypertension and chronic bronchitis in the healthcare access panel are very good , compared to the correspondence of the german national health survey ( tab . there is no suspicion of a systematic difference among both data sources of disease prevalence . this reconfirms that the access sample is not materially biased if compared with a good - quality representative random sample survey of the same source population - at least for that kind of information . . just as often , however , will the results of analyses in the access panel be sufficient or even preferable concerning cost - effectiveness . advantages of the access panel approach might be :  the results can be obtained in a relatively short period of time ( a few weeks or months ) , at least as compared with a specific designed population - based survey . usually , the result can be generalised for the source population .    for a majority of social and health - related issues , matters of health services research or e.g. drug utilisation , the results of the access panel will be usually sufficient to give valid answers . surveys of very large groups are possible if rare phenomena have to be studied . even for small sub - groups with specific characteristics sufficient numbers of participants will be available in most cases - which are often a problem difficult to overcome for planned population surveys due to the costs . the costs are considerably lower than for a planned cross - sectional random sample survey . even follow - up studies are possible : if certain information has been documented years ago , changes over time can be monitored ( historic cohort approach ) . comparisons among different countries are possible since access panels , using the same method , have been established in many countries of europe and in other continents . disadvantages can be :  the methodological design of the access panel can not be changed , although some helpful minor modifications can be discussed for individual situations . certain bias forms can be inherent in any self - selected cohort unless sufficient evidence for the contrary can be provided . real response rates can not be determined due to the self - selective nature of the panel . nonetheless , non - response rates of the panel members are important to know . the representativeness for the source population needs to be specifically discussed when results of the access panel should be generalized . however , this is also the case , to a lesser degree , for planned population - based random sample surveys . surveys using the access panel are a valuable methodological supplement to the conventional health survey approaches to get rapid answers for most of the health - relevant issues . the federal statistical office of germany itself is working on a pilot study for testing an access panel approach . the presented examples from germany demonstrated a high degree of validity of access panel results , i.e. in comparison with population - based data sources ( surveys as well as national statistics ) , even if age - specific distributions of chronic diseases are considered .   since the data were collected by mailed questionnaires only self - perceived disease will be reported . however , methodological issues of self - selection of the access panel need to be discussed for every specific study . the access panel network is in a rapid development in order to facilitate comparative studies on a broad international level . the conclusions about the cost - effectiveness of the household panel approach correspond very well with the experiences with the european household panel of eurostat .
background : random sample surveys of the population are time consuming and expensive , particularly if international sampling is planned.method : the healthcare access panel was developed as an alternative to face to face or telephone health survey interviews to estimate prevalence or even incidence rates of health - relevant variables in the population . 
 it is the objective of this paper to demonstrate the validity of health - related data obtained with the healthcare access panel compared with results from other , population - based data sources . 
 the example is germany , where the panel consists of more than 78,000 individuals aged between 0 and 79 years . 
 results : the healthcare access panel reflects the population concerning age , sex , and regional structure with a good correlation . the hospitalisation rate obtained with the panel matches the official national hospital discharge statistics . 
 annual consultations with major medical disciplines were found to be almost identical in the healthcare access panel as compared with the german national health survey ( gnhs ) . 
 the healthcare access panel data matched the gnhs prevalence results of self - reported medical conditions / diseases . 
 advantages and disadvantages of the healthcare access panel compared with specially designed population field surveys are discussed . 
 conclusion : it is worthwhile to consider the healthcare access panel approach as a cost - effective alternative to other population - based data collection methods under many circumstances , i.e. considering the specific methodological pros and cons as necessary for any other method .