PIN in the total population register at statistics Sweden
The PIN is the unique identifier in the TPR . The TPR includes data on name, place of residence, sex, age, civil status, place of birth (country, county, parish), citizenship, immigration (date, country, ground for settlement), and relations (married couples, child–parent). Until the year 2000, PINs were sometimes assigned also to individuals who had not entered into the TPR , but since that year individuals that do not qualify for a PIN receive a personal coordination number instead (see below). On Dec 31 2007 the total population of Sweden was 9,182,927. The estimated number of PIN’s in Sweden since 1969 is however, larger, and has been estimated to some 13,500,000 until Dec 31 2007 (Statistics Sweden).
Structure of the PIN
The PIN has three parts: date of birth, a three-digit birth number, and a check digit. The three-digit birth number is sex-specific.
Date of birth is listed as year, month, and day (e.g. 640823). This is followed by a three-digit birth number (e.g. 323) and a check digit (e.g. 4). The birth number can take on any value between 001 and 999. It is odd for men (e.g. 999) and even for women (998), i.e. the third digit is odd for men but never for women. The combination of a specific date of birth and a specific birth number will allow all Swedish individuals to have a unique PIN. Until the 1980s, the birth numbers could be linked to county of birth (not country of birth), but since 1990, birth numbers are drawn from a national pool of numbers. Between the date of birth and the birth number is a hyphen (“-”). The hyphen should in fact be changed into a plus sign the year an individual attains 100 years of age. This is to differ between individuals with the same birthday and same birth year but in different centuries. Hence individuals born in the 1900s (and being above 100 years old) and those born in the 2000s (below 100 years old) respectively should be listed as e.g. 010203+6578 and 010203-6578 respectively. However, the plus sign is seldom used, and in more and more IT systems the century is also included in the PIN (e.g. 19010203-6578).
The check digit is calculated according to the modulus-10-method, assigning alternating weights of two or one to the first nine digits of the PIN (Fig. 1). The purpose of the check digit is to check the correctness of the PIN, and such checks should always be performed prior to register linkages.
Assignment of the PIN
Every birth in Sweden must be reported to the Tax Board. The birth of a child is reported by the obstetric department, or if the birth takes place outside hospital, by the midwife, or if no midwife is present at the delivery, by the parents of the newborn child. According to Swedish law, the birth of the newborn child must be reported within 1 month after birth. It is estimated that 90% of all births and 93% of all deaths are reported to Statistics Sweden within 10 days, and 98 and 100% respectively within 30 days. A person who has once been assigned a PIN cannot have a new PIN other than for special reasons.
Immigrants without a PIN will also receive a PIN if they intend to stay in Sweden for at least 1 year. Immigrants who do not fulfil this criterion, but who e.g. are taxed in Sweden or who use the Swedish social security system will be assigned a coordination number.
Assignment of the coordination number
Coordination numbers were introduced in the year 2000, and are assigned to residents who are not registered in the TPR (mostly individuals that intend to stay in Sweden <1 year) . These individuals do not receive a PIN. The coordination numbers are assigned by the National Tax Board, and enables different government agencies to collaborate around and identify individuals that stay in Sweden for a short time. In the years 2000–2007, some 350,000 individuals received a coordination number . Uses of the coordination number include: tax payment, police registers, use of social security, seamen on a visit to Sweden, driving license purpose and car ownership, and diplomats. In the future, it is possible that diplomats residing in Sweden will also enter the TPR. The structure of the coordination number is very similar to that of the PIN, except that the value “60” is added to the day of birth digit. E.g. an individual born on the 13th of July 1969 will have a coordination number that begins with “690773” (13 + 60 = 73 on the “day of birth position”).
Although individuals with coordination number often frequent medical care, these individuals are not registered in the national health registers or in the TPR. Hence non-permanent residents with coordination numbers will not be sampled in national register studies in Sweden.
Judicial regulation of the PIN
All jurisdiction of the PIN can be found in the Population Registration Act §18 (1991:481).
Use of the PIN
When the PIN was established in 1947 it was primarily intended as an efficient means of identifying an individual. With the introduction of computerized national registers, the PIN has become a vital component of register linkages for research purposes [4–6], and is used as the key number in all national linkages. Today the PIN is extensively used in the public administration. In more and more medical research, the PIN is also used as the linkage tool between national register data and data collected through patient charts  or biobank data .
In health care, the PIN is used for vital statistics (date of birth, date of death), but it is also the unique identifier and the key variable when matching between different registers including The Patient Register (with inpatient and outpatient data), Cancer Register, Cause of Death Register, Medical Birth Register, and e.g. the National surveillance system of infectious diseases.
The most important use of the PIN in Swedish health care is however to trace patients and their medical records. The PIN enables efficient handling of referrals and referral letters, and is a means of identifying patients handled by different health care staff such as physicians, nurses, occupational therapists, physiotherapists etc. The PIN drastically reduces the risk of duplication errors, and can also separate the identities of same-sex twins. The PIN is also used as a marker for age. Traditionally individuals aged below 18 years are referred to the department of paediatrics, while adults are referred to departments primarily caring for adults.
Outside health care, the PIN is used for population statistics, migration, taxation, education, passports, income, and social security etc. It is also used for conscription purposes and by insurance companies. In real life, residents may be asked for their PIN for such various tasks as subscribing to a newspaper and hiring a car.
The vital statistics of Sweden is maintained by Statistics Sweden and updated daily regarding births, migrations, deaths, and marital status.
The PIN is the basis for efficient register linkages, and its use allows for easier (better) evaluations of Swedish health care, than in countries where residents lack a unique identifier.
Several authorities handle register linkages for health research purposes and the two major operators are Statistics Sweden and the National Board of Health and Welfare. Their areas of responsibility differ, and many register linkages involve both agencies (Figs 2, 3). Figure 2 presents the initial data linkage procedure in a project that examined the risk of multiple sclerosis among individuals with coeliac disease . Figure 3 presents a possible linkage between cardiovascular morbidity data collected by a researcher and data from the national health registers. The linkage in Fig. 3 would enable the researcher to study cause-specific death, risk of cancer, risk of e.g. thyroid disease, and risk of adverse pregnancy outcome in patients with heart failure, myocardial infarction or stroke etc.