Sample design

Cohort A

Stratification

  1. The prefectures of Japan were classified into eight blocks.

  2. The number of cities in each block. Within each block, the cities were further classified and stratified by city size as follows.

    1. 13 major cities (Sapporo, Sendai, Chiba, Tokyo metropolitan area, Yokohama, Kawasaki, Nagoya, Kyoto, Osaka, Kobe, Hiroshima, Kitakyushu, Fukuoka)

    2. (Note) Cities in this section are defined as areas where municipal government was in effect as of April 1, 1993.

    3. Towns or villages

Sample distribution

Depending on the size of the estimated population in each city-size stratum, a sample size of 1,500 was proportionally distributed, taking into account the age structure and marital status (the number of people aged 24-34 by age and marital status as of March 31, 1992).

Sampling

  1. The survey area established at the time of the 1990 census was used as the survey point to serve as the primary extraction unit.

  2. The number of survey points (census tracts) The number of survey sites (census tracts) was determined by calculating the number of samples assigned to each stratum so that the sample size per survey site would be 12.

  3. Extraction of study sites (study area) was carried out using the equal interval method by calculating the extraction intervals as follows for the strata where the number of extraction sites within a stratum was assigned to two or more sites.

\[\frac{\text{Number of survey areas in strata (total)}}{\text{Number of survey sites extracted in stratum}} = \text{Extraction interval}\]
  1. The order of cities, towns, and villages in each stratum in the extraction follows the order of the “Prefectural and Municipal Code Table” at the time of the 1990 census.

  2. The respondents at the survey points were extracted from the Basic Resident Register using the equal interval extraction method according to the address of the survey point (specifying the town, street, city block, street number, etc.).

  3. Since this survey was designed to be a survey with a specified number of completions, a reserve respondent 3 was added to the regular respondent 1 above.

  4. The number of samples by stratum and the number of survey sites obtained as a result of the above work are shown in Table-1.

Table 1 Estimated population size, sample size, and number of survey sites by stratum for Cohort A

Table 1-1 Estimated population size

13 major cities

Other cities

Towns or villages

Total

Hokkaido

272,755

328,511

177,644

778,910

Tohoku

143,956

710,759

439,852

1,294,567

Kanto

2,261,067

3,035,727

612,586

5,909,380

Chubu

330,121

1,982,543

787,642

3,100,306

Kinki

791,651

1,684,208

331,368

2,807,227

Chugoku

158,655

578,830

220,257

957,742

Shikoku

0

343,032

175,300

518,332

Kyushu

327,575

1,019,476

580,010

1,927,061

Total

4,285,780

9,683,086

3,324,659

17,293,525

Table 1-2 Sample size

13 major cities

Other cities

Towns or villages

Total

Hokkaido

24

36

12

72

Tohoku

12

60

36

108

Kanto

192

264

60

516

Chubu

36

168

72

276

Kinki

72

144

24

240

Chugoku

12

48

24

84

Shikoku

0

36

12

48

Kyushu

24

84

48

156

Total

372

840

288

1,500

Table 1-3 Number of survey sites

13 major cities

Other cities

Towns or villages

Total

Hokkaido

2

3

1

6

Tohoku

1

5

3

9

Kanto

16

22

5

43

Chubu

3

14

6

23

Kinki

6

12

2

20

Chugoku

1

4

2

7

Shikoku

0

3

1

4

Kyushu

2

7

4

13

Total

31

70

24

125

Cohort B

Stratification

The sample design for Cohort B was the same as that for Cohort A except for the sample size distribution. The distribution of Cohort A respondents closely matched that of the national census, with the only exception being that the proportion of unmarried single individuals was slightly lower than that in the national census. Accordingly, the proportion of unmarried single individuals in Cohort B was taken into account when allocating the number of samples.

Sample distribution

Depending on the size of the estimated population in each city-size stratum, a sample size of 500 was allocated proportionally, taking into account the age structure and marital status (number of people aged 24-27 as of March 31, 1996, by age and marital status, and number of single-person households with no marital status). The sample size by stratum and the number of survey sites are shown in Table-2.

Sampling

For each official respondent, reserve respondents were selected as follows depending on marital status and household circumstances: 3 reserve respondents for each married respondent, 3 reserve respondents for each unmarried respondent not in a single household, and 5 reserve respondents for each unmarried respondent in a single household.

Table 2 Estimated population size, sample size, and number of survey sites by stratum for Cohort B

Table 2-1 Estimated population size

13 major cities

Other cities

Towns or villages

Total

Hokkaido

315,837

354,942

163,782

834,561

Tohoku

165,648

717,759

403,002

1,286,409

Kanto

2,759,343

3,683,433

623,364

7,066,140

Chubu

385,263

2,239,332

831,210

3,455,805

Kinki

942,807

1,994,082

345,852

3,282,741

Chugoku

180,561

607,938

209,568

998,067

Shikoku

0

359,337

168,459

527,796

Kyushu

363,696

1,041,798

557,448

1,962,942

Total

5,113,155

10,998,621

3,302,685

19,414,461

Table 2-2 Sample size

13 major cities

Other cities

Towns or villages

Total

Hokkaido

8

10

4

22

Tohoku

4

20

9

33

Kanto

72

98

14

184

Chubu

9

61

20

90

Kinki

25

55

5

85

Chugoku

4

15

4

23

Shikoku

0

10

4

14

Kyushu

10

26

13

49

Total

132

295

73

500

Table 2-3 number of survey sites

13 major cities

Other cities

Towns or villages

Total

Hokkaido

2

3

1

6

Tohoku

1

5

3

9

Kanto

16

22

5

43

Chubu

3

14

6

23

Kinki

6

12

2

20

Chugoku

1

4

2

7

Shikoku

0

3

1

4

Kyushu

2

7

4

13

Total

31

70

24

125

Cohort C

Stratification

  1. The prefectures of Japan were classified into eight blocks.

  2. The number of cities in each block. Within each block, the cities were further classified and stratified by city size as follows.

    1. 14 major cities (Sapporo, Sendai, Saitama, Chiba, Tokyo metropolitan area, Yokohama, Kawasaki, Nagoya, Kyoto, Osaka, Kobe, Hiroshima, Kitakyushu, Fukuoka)

    2. (Note) Cities in this section are defined as areas where municipal government was in effect as of April 1, 1993.

    3. Towns or villages

Sample distribution

Depending on the size of the estimated population in each city size stratum, 836 samples were proportionally distributed, taking into account the age structure and marital status (number of people aged 24-29 years as of March 31, 2003, by age and marital status). The sample size and number of survey sites by stratum are shown in Table-3.

Sampling

Between 4 and 9 respondents were selected for each survey site depending on the age and marital status distributions for each city size stratum. Reserve respondents were identified as follows depending on marital status and household circumstances: 3 reserve respondents for each married respondent, 4 reserve respondents for each unmarried respondent not in a single household, and 7 reserve respondents for each unmarried respondent in a single household

Table 3 Estimated population size, sample size, and number of survey sites by stratum for Cohort C

Table 3-1 Estimated population size

14 major cities

Other cities

Towns or villages

Total

Hokkaido

540,756

613,383

265,566

1,419,705

Tohoku

317,436

1,244,232

665,448

2,227,116

Kanto

4,679,379

6,137,133

1,135,146

11,951,658

Chubu

614,394

4,021,920

1,447,863

6,084,177

Kinki

1,565,124

3,533,046

628,206

5,726,376

Chugoku

337,476

1,169,547

385,989

1,893,012

Shikoku

0

681,645

299,001

980,646

Kyushu

675,927

1,902,615

962,382

3,540,924

Total

8,730,492

19,303,521

5,789,601

33,823,614

Table 3-2 Sample size

14 major cities

Other cities

Towns or villages

Total

Hokkaido

11

15

6

32

Tohoku

6

29

17

52

Kanto

118

158

29

305

Chubu

19

97

35

151

Kinki

40

87

14

141

Chugoku

8

28

9

45

Shikoku

0

18

6

24

Kyushu

18

45

23

86

Total

220

477

139

836

Table 3-3 Number of survey sites

14 major cities

Other cities

Towns or villages

Total

Hokkaido

2

3

1

6

Tohoku

1

5

3

9

Kanto

17

21

5

43

Chubu

3

14

6

23

Kinki

6

12

2

20

Chugoku

1

4

2

7

Shikoku

0

3

1

4

Kyushu

2

7

4

13

Total

32

69

24

125

Cohort D

Stratification

  1. The prefectures of Japan were classified into eight blocks.

  2. The number of cities in each block. Within each block, the cities were further classified and stratified by city size as follows.

    1. 18 major cities (Sapporo, Sendai, Saitama, Chiba, Tokyo metropolitan area, Yokohama, Kawasaki, Niigata, Shizuoka, Hamamatsu, Nagoya, Kyoto, Osaka, Sakai, Kobe, Hiroshima, Kitakyushu, Fukuoka)

    2. (Note) Cities in this section are defined as areas where municipal government was in effect as of April 1, 1993.

    3. Towns or villages

Sample distribution

Depending on the size of the estimated population in each city size stratum, 836 samples were proportionally distributed, taking into account the age structure and marital status (number of people aged 24-28 years as of March 31, 2008, by age and marital status). The sample size and number of survey sites by stratum are shown in Table-4.

Sampling

Between 4 and 9 respondents were selected for each survey site depending on the age and marital status distributions for each city size stratum. Reserve respondents were identified as follows depending on marital status and household circumstances: 3 reserve respondents for each married respondent, 4 reserve respondents for each unmarried respondent not in a single household, and 7 reserve respondents for each unmarried respondent in a single household

Table 4 Estimated population size, sample size, and number of survey sites by stratum for Cohort D

Table 4-1 Estimated population size

18 major cities

Other cities

Towns or villages

Total

Hokkaido

66,227

69,550

24,681

160,458

Tohoku

37,916

175,721

46,499

260,136

Kanto

539,215

709,813

64,797

1,313,825

Chubu

133,722

451,572

69,476

654,770

Kinki

206,915

385,174

34,559

626,648

Chugoku

37,244

155,344

15,805

208,393

Shikoku

0

92,753

15,981

108,734

Kyushu

85,115

290,154

65,475

440,744

Total

1,106,354

2,330,081

337,273

3,773,708

Table 4-2 Sample size

18 major cities

Other cities

Towns or villages

Total

Hokkaido

11

11

4

26

Tohoku

7

29

8

44

Kanto

89

118

10

217

Chubu

23

75

12

110

Kinki

34

63

5

102

Chugoku

6

26

3

35

Shikoku

0

15

3

18

Kyushu

14

48

11

73

Total

184

385

56

625

Table 4-3 Number of survey sites

18 major cities

Other cities

Towns or villages

Total

Hokkaido

2

3

1

6

Tohoku

1

7

2

10

Kanto

18

22

3

43

Chubu

5

17

3

25

Kinki

7

11

2

20

Chugoku

1

6

1

8

Shikoku

0

4

1

5

Kyushu

2

9

2

13

Total

36

79

15

130

Cohort E

Stratification

  1. The prefectures of Japan were classified into eight blocks.

  2. The number of cities in each block. Within each block, the cities were further classified and stratified by city size as follows.

    1. 21 major cities (Sapporo, Sendai, Saitama, Chiba, Tokyo metropolitan area, Yokohama, Kawasaki, Sagamihara, Niigata, Shizuoka, Hamamatsu, Nagoya, Kyoto, Osaka, Sakai, Kobe, Okayama, Hiroshima, Kitakyushu, Fukuoka, Kumamoto)

    2. (Note) Cities in this section are defined as areas where municipal government was in effect as of April 1, 1993.

    3. Towns or villages

Sample distribution

Depending on the size of the estimated population in each city-size stratum, a sample size of 625 was proportionally distributed, taking into account the age structure and marital status (the number of people aged 24-34 by age and marital status as of March 31, 1992).

Sampling

Between 4 and 9 respondents were selected for each survey site depending on the age and marital status distributions for each city size stratum. Reserve respondents were identified as follows depending on marital status and household circumstances: 3 reserve respondents for each married respondent, 4 reserve respondents for each unmarried respondent not in a single household, and 7 reserve respondents for each unmarried respondent in a single household

Table 5 Estimated population size, sample size, and number of survey sites by stratum for Cohort E

Table 5-1 Estimated population size

21 major cities

Other cities

Towns or villages

Total

Hokkaido

60,858

58,665

20,731

140,254

Tohoku

34,186

151,987

40,590

226,763

Kanto

529,768

631,066

47,369

1,208,203

Chubu

125,493

419,440

50,945

595,878

Kinki

194,725

345,567

29,450

569,742

Chugoku

54,925

122,797

12,914

190,636

Shikoku

0

83,412

13,903

97,315

Kyushu

101,576

248,224

53,685

403,485

Total

1,101,531

2,061,158

269,587

3,432,276

Table 5-2 Sample size

21 major cities

Other cities

Towns or villages

Total

Hokkaido

11

11

4

26

Tohoku

6

28

8

42

Kanto

96

115

8

219

Chubu

23

76

10

109

Kinki

35

63

5

103

Chugoku

10

23

2

35

Shikoku

0

15

3

18

Kyushu

18

45

10

73

Total

199

376

50

625

Table 5-3 number of survey sites

21 major cities

Other cities

Towns or villages

Total

Hokkaido

2

2

1

5

Tohoku

1

6

2

9

Kanto

19

23

2

44

Chubu

5

15

2

22

Kinki

7

13

1

21

Chugoku

2

5

1

8

Shikoku

0

3

1

4

Kyushu

4

9

2

15

Total

40

76

12

128