The personal identity number (PIN) was introduced in 1947 and then consisted of date of birth and a three-digit number. From 1947 and onwards, every individual that has resided in Sweden on a permanent basis (and been recorded in the Total population register, TPR) has been assigned a PIN. In 1967, a check digit was added to the three-digit number. The check digit verifies that data of birth and the three-digit number are correct. In 1991, when the responsibility for the local population registers was moved from the local parishes to the local tax offices, the National Tax Board took over the full responsibility for the Swedish PIN. When the local population registers were computerized in 1967, Statistics Sweden established the TPR.

In 1997, the National Tax Board initiated a new notification system with partially new data. As of today (year 2009), all notifications are delivered from the National Tax Board to other administrations, including Statistics Sweden, on a daily basis. Statistics Sweden stores all notifications with updates in a notification database.

The large number of individuals with (true or wrongly assigned) birth dates in the 1950s and 1960s illustrates the risk of a shortage of PINs. Due to the current construction of the PIN, there are a maximum of 500 male and 499 female PINs, and it has been estimated that in 5 years PINs referring to certain days of births will not be available [3]. Also in the future, will Sweden and other counties face large numbers of migrants with birthdays on the 1st of Jan and the 1st of July.

Increased awareness of the high stress on the current PIN system has led to a government investigation on the future structure of the PIN. Given that a lot of the digital infrastructure in Sweden is conditioned on a 10–12 digits PIN (12 digits when the PIN includes the century), the Swedish Council of Legislation is currently considering a change of law, that would allow future immigrants for which there are no PINs corresponding to their birth date, to be assigned a PIN where the “day position” corresponds to a date just before or after his/her actual birth date. Information on the exact date of birth would, however, be stored separately in the TPR. There are no plans to change existing PINs or the structure of the coordination numbers [3].

But the PIN also allows medical data to be used for educational purposes, research and quality assurance schemes. Large medical databases such as the Swedish Cancer Register or the Swedish Patient Register, built around the PIN, create additional value to society. The PIN enables researchers to merge such registers and to examine an array of questions, including the long-term consequences of preterm birth [13] or certain diseases [14], the medical consequences of alcohol abuse [15], or the association between a medical event and human behaviour [16]. Hence, the PIN allows researchers to estimate morbidity and mortality in patients. Such research will not only optimize health care resource allocation but more importantly improve the management of both current and future patients. Through the PIN it is possible to trace virtually any patient. The medical outcome of a patient (e.g. with increasing age a prostate cancer may become obvious) can be used to evaluate sensitivity and specificity of new diagnostic techniques tested on both historic and new blood samples. Finally, the natural course of disease (as recorded in registers and patient charts) serves to educate medical students.

The fact that historic medical data often benefit the patient him-/herself is an important reason why individual patients cannot withhold or withdraw their medical data from the national health registers, or request that such register data be anonymised (i.e. that all links to their PIN is deleted). Such rights would harm both medical care and the quality of medical research. Considering that withholding data is not an option for Swedish patients it is difficult to estimate the proportion of individuals who had this been possible would have requested anonymisation, deletion or restricted use of their medical data. However, in a study on patient’s refusal to consent to storage and use of samples in Swedish biobanks [17] only 1 in 690 patients objected to the storage and use of such data for research purposes, and even fewer were willing to complete a dissent form. Although a refusal of 1/690 individual will not affect study power in medical research, such refusals may cause some bias since they are unlikely to be non-differential with regards to background factors, socioeconomic status, ethnicity, and morbidity.

According to current Swedish regulation, the use of national register data for research purposes does not require informed consent. We argue that the current situation benefits patients and society, and that informed consent should not be required for large-scale medical research. A number of arguments can be put forward to defend this ethical position (equally relevant to biobank data [18]).

(1) Some patients will not understand the consequences of their objections to the use of register-based health data. (2) The impossibility to acquire the approval of everyone would reduce the statistical power of most studies. (3) There is an obvious risk that consent would be especially difficult to obtain in high-risk groups where positive outcomes are most frequent, in children, and in immigrants with limited knowledge of the Swedish language. This conflicts with the principle of justice and equality [19] that stipulates that individuals should not be discriminated against due to inability to consent or to understand the meaning or need of medical research. (4) Relatives may find questions on the use of medical data from their “dead mother or father” for research purposes lacking in respect. (5) The costs of obtaining the consent of millions of patients with health data would be exorbitant and prohibit most large-scale research. The cost is however not always a valid argument, and in small-scale register-linkages it may be feasible to seek patients’ consent before carrying out the study. Finally (6), it should be remembered that the public is not without voice in matters of any medical research (including that based on the PIN). When a register contains identifiable data (through the PIN, name or any other unique identifier), each individual has a right to obtain a copy of his/her data in that register. Furthermore, it is preferable to inform the public of large-scale ongoing research projects through the media, including what groups of people are being involved (e.g. men born between 1913 and 1923).

Hence, it may be concluded, that although large-scale register-based studies do not routinely involve personal consent), researchers in Sweden are nevertheless expected to protect the integrity of participating individuals and meet the demands of study participants whenever possible.