Baseline Survey of JPHC Study-Design and Participation Rate

The data collection from cohort subjects at baseline is the core work for prospective study as well as follow-up. We set up 140,420 cohort subjects (68,722 men and 71,698 women) (61,595 in 1990 as Cohort I and 78,825 in 1993 as Cohort II) based on resident registry of 29 districts under 11 Public Health Center areas and baseline survey were submitted for them. The survey consisted of the following three components: (1) self-administered questionnaire survey, (2) collection of blood samples (plasma and buffy coat) for deep-freezed storage and (3) collection of health check-up data. All survey were completed during the first five year of each study. Among all cohort subjects, 113,461 (81%) (53,375 men and 60,086 women, 50,245 in Cohort I and 63,216 in Cohort II) returned the questionnaire and 49,011 (35%) (18,159 men and 30,852 women, 24,637 in Cohort I and 24,374 in Cohort II) provide their blood. The health check-up data were collected from 47,910 (34%) (17,276 men and 30,664 women, 23,311 in Cohort I and 24,599 in Cohort II). These data and blood samples serve as basis for the Japan Public Health Center-based prospective Study on cancer and cardiovascular diseases (JPHC Study) . J Epidemiol, 2001; 11 (Suppl): S24-S29.


INTRODUCTION
The data collection from cohort subjects at baseline is the core work for prospective study as well as follow-up.The data obtained from questionnaire is usually served as baseline data in most prospective studies.However these data are subjective and can be unreliable in some factors.More objective information is useful and thus human materials such as blood, tissue and toenail are frequently collected and stored for future use in prospective studies.

METHODS
The Japan Public Health Center-based prospective Study on cancer and cardiovascular diseases (JPHC Study) was initiated by 4 population cohorts and a health checkup cohort (Cohort I) in 1990 and it merged 5 population cohorts and two Suita city cohorts (Cohort II) in 1993.

Subjects CohortI
As of January 1, 1990, we established a population-based cohort of 54,498 residents (27,063 men and 27,435 women) who registered their address in 14 administrative districts (city , town or village) supervised by four Public Health Center (PHC) areas: 12,291 from Ninohe city and Karumai town in Ninohe PHC area, Iwate prefecture , 15,782 from Yokote city and Omonogawa town in Yokote PHC area , Akita prefecture, 12,219 from Usuda, Saku, Koumi , Kawakami towns and Yachiho, Minami-aiki, Kita-aiki, Minami-maki villages in Saku PHC areas, Nagano prefecture , 14,206 from Gushikawa city and Onna village in Ishikawa PHC area , Okinawa prefecture, and who was born from January 1 , 1930 to December 31, 1949 (40 to 59 years of age) .We further included 7,097 participants (2,919 men and 4 ,178 women) of health checkup program in Katshushika PHC area in Tokyo metropolis from the fiscal year 1990 to 1994 (2 ,440 in 1990, 2,211 in 1991, 173 in 1992, 1,033 in 1993, and 1 ,240 in 1994), in which all residents with 40 and 50 year-old were invited.Five PHC areas were selected based on variation in mortality rate of stomach cancer for our previous ecological study, in which randomly selected subjects were intensively examined 1,2,3,).

Cohort II
As of January 1, 1993, we established a population-based cohort of 62,398 residents (30,651 men and 31,747 women) who registered their address in 13 administrative districts (city, town or village) supervised by five PHC areas: 21,488 from Tomobe town and Iwase town in Kasama PHC area, Ibaraki prefecture, 3,571 from Oguni town in Kashiwazaki PHC area, Niigata prefecture, 8,606 from Kagami town and Noichi town in Tosayamada PHC area, Kochi prefecture, 14,624 from Uku town, Ojika town, Shin-uonome town, Arikawa town, Kamigoto town and Narao town in Arikawa PHC area, Nagasaki prefecture, and 14,109 from Hirara city and Gusukube town in Miyako PHC area, Okinawa prefecture, and who was born from January 1, 1923 to December 31, 1952.In Suita city in Suita PHC area, Osaka prefecture, two different cohorts were set up.The first cohort (Suita 1) was defined as all 9,747 residents (4,793 men and 4,954 women) in Suita city with 40 or 50 year-old in the fiscal year 1993, because they were invited to the comprehensive health checkup program conducted by the city.The second cohort (Suita 2) was defined as a part of the Suita study 4), in which subjects were arbitrarily selected based on the population registry of the city, in the years 1989 through 1992 and aged 30 to 79 years, stratified by sex and 10 year age group.The 6,680 subjects (3,296 men and 3,384 women) with aged 40 to 69 years as of April 1, 1993 were used for the JPHC study.Six PHC areas were selected considering geographical distribution and feasibility.

Baseline Survey
Questionnaire: A self-administered questionnaire was submitted to all cohort subjects and asked to report their lifestyle such as socio-demographic situation, personal medical history, smoking and drinking history, and dietary habits.The questionnaire used in Cohort II was modified in several items.The questionnaire was distributed mostly by hand or partly by mail in 1990 (as a rule) in 4 populations in Cohort I and in 1993 (as a rule) in 5 populations in Cohort H.The incomplete answer was supplemented by telephone interview.In Katsushika PHC area, questionnaire was interviewed on the occasion of health checkup from 1990 to 1994.In Suita PHC area, the questionnaire was mailed to all the subjects from 1993 to 1995 and supplemented by interview for participants of health checkup on that occasion or by telephone interview for those who did not attend the health check-up.
Blood and health checkup: A total of 10 ml blood was provided voluntarily by cohort subjects and gathered into heparinized tube in the occasion of health checkup program    * Subjects of health check-up program at 40 and 50 years of age , ** Randomly selected subjects their plasma and huffy layer at -80.We also obtained health checkup data from 19,292 (31%) population cohort, 6,476 (21%) men and 12,312 (40%) women, and 5,307 (32%) health checkup cohort, 1,993 (25%) men and 3,314 (40%) women.

DISCUSSIONS
The JPHC Study includes 29 study sub-areas (city, town or village level) from 11 PHC area.These sub-areas are divided into 3 types: urban city with over 300,000 populations (Katsushika ward and Suita city), local city with over 20,000 populations (Ninohe, Yokote, Gushikawa and Hirara cities), rural town or village (the other 23 towns or villages).The questionnaire and the collection of blood and checkup data were applied only for participants of health checkup program in Katsushika area and therefore the response rate was substantially higher than the other areas.Although the method applied in two sub-areas in Suita city were slightly different from population-based cohort, the subjects were both extracted from population registry and not participants of health checkup program.The response rates to the questionnaire tended to be higher (87%) in 23 rural town or villages, lower (66%) in urban city (Suita city) and intermediate (73%) in 4 local cities.The same trend was also observed for the collection rates of blood and checkup data which were only collected from the participants of local healthcheck up program, although the rates were lower in a Gushikawa city when compared with other local cities.
The response rates were consistently lower in men than in women.The sexual differences were more marked in the collection rates of blood and checkup data.This is because women tend to participate in health checkup program provided by local government which is our major source of checkup data and blood collections.Men usually take a health checkup in their workplace.
In summary, among 140,420 targeted subjects, we created a database with information from 113,461 (81%) questionnaires regarding lifestyle and from 47,910 (34%) health checkup data.We also stored 3 aliquotes of plasma and one aliquote of buffy coat from 49,011 subjects.These data and blood samples serve as basis for JPHC Study.

Table la .
Participants of baseline survey, cohort I.
* Participants of health check -up program at 40 and 50 years of age

Table lb .
Participants of baseline survey , cohort I males.
* Participants of health check-up program at 40 and 50 years of age

Table 2b .
Participants of baseline survey, cohort II males.Subjects of health check-up program at 40 and 50 years of age , ** Randomly selected subjects *

Table 2c .
Participants of baseline survey, cohort II females.