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Finland Sample Design

World Health Survey 2002 – Sampling Plan

 1. Introduction

This is a stratified cluster sampling, where clusters are formed from zip code areas (total number: 2865). Primary stratification is based on municipality data and secondary stratification is based on zip code areas.

2. Primary stratification

The primary stratification is based on two dimensions:

  1. North-South dimension grouped the municipalities according to NUTS 2 into three groups: South (NUTS 2 = 1,2), Central Finland (NUTS 2 = 3,4) and Northern Finland (NUTS 2 = 5)
  1. Urban-rural dimension was used to form two groups: 1) Urban municipalities and 2) semi-urban and rural municipalities

By linking these two dimensions six primary level strata are obtained.  The Capital Region ( Helsinki , Espoo , Vantaa , Kauniainen) forms an individual stratum:

Number of people aged 18+

 

Capital region

Urban

Semi-urban/rural

Southern

748953

1076445

685277

Central

0

445502

633891

Northern

0

192810

222939

Since the sample size is 1000 persons and one starting/sampling point contains six interviews, the total number of starting/sampling points is 167. Starting points are distributed among strata in accordance to the population (aged 18+).  Thus the distribution of starting points is as follows:

Sample sizes (number of sampling/starting points)

 

Capital region

Urban

Semi-urban/rural

Southern

31

45

29

Central

0

19

26

Northern

0

8

9

3. Secondary stratification

The second stage stratification groups zip code areas within the first stage strata in such a way, that the second stage strata are as homogeneous as possible in terms of socio-economic dimensions. This increases the accuracy of estimation. In total there are 16 second stage strata. Since there is not very much information available from zip code areas, it was decided to use mean income in the capital region and proportion of apartment buildings in other regions as the stratification variable. At each first stage stratum the number of starting points was distributed as equally as possible amongst the second stage strata. From this followed, that within each first stage stratum each second stage stratum contains approximately similar number of people.

Capital region was divided into four second stage strata.

 

Stratum 1

Stratum 2

Stratum 3

Stratum 4

Maximum mean income in zip code area (€)

15749

17466

19002

30384

Southern Finland was divided into four second stage strata.

 

Urban

Semi-urban/rural

Stratum 5

Stratum 6

Stratum 7

Stratum 8

%-share of people living in apartments

>53,5%

<=53,5%

>12,5%

<=12,5%

Central Finland was divided into four second stage strata.

 

Urban

Semi-urban/rural

Stratum 9

Stratum 10

Stratum 11

Stratum 12

%-share of people living in apartments

>49%

<=49%

>7,5%

<=7,5%

Northern Finland was divided into four second stage strata.

 

Urban

Semi-urban/rural

Stratum 13

Stratum 14

Stratum 15

Stratum 16

%-share of people living in apartments

>36,5%

<=36,5%

>2,5%

<=2,5%

The number of people and clusters and the sample sizes are in the following table. The total number of clusters was reduced to 2830, because 35 zip code areas have no inhabitants.

 

Number of inhabitants

Number of clusters

Sample size

Capital region

 

Total

748953

153

31

 

Stratum 1

194324

32

8

 

Stratum 2

192679

40

8

 

Stratum 3

189521

43

8

 

Stratum 4

172429

39

7

Southern Finland

Total

1761722

1158

74

Urban

1076445

347

45

 

Stratum 5

550183

116

23

Stratum 6

526262

231

22

Semi-urban/rural

685277

811

29

 

Stratum 7

354454

143

15

Stratum 8

330823

668

14

Central Finland

Total

1079393

1095

45

Urban

445502

176

19

 

Stratum 9

234475

64

10

Stratum 10

211027

112

9

Semi-urban/rural

633891

919

26

 

Stratum 11

316385

126

13

Stratum 12

317506

793

13

Northern Finland

Total

415749

423

17

Urban

192810

73

8

 

Stratum 13

95957

25

4

Stratum 14

96853

48

4

Semi-urban/rural

222939

350

9

 

Stratum 15

123993

66

5

Stratum 16

98946

284

4

Total

4005817

2830

167

The number of starting/sampling points inside each stratum is in a direct relation to the number of inhabitants in each stratum. Therefore proportional allocation has been used.  Inside each stratum, clusters (zip code areas) have been picked using PPS-sampling and inside each picked cluster the same sample size (6 interviews) has been used. From this follows, that each person has similar probability to be picked into the sample – tn=1000/4005817=0,0002496. In this case estimators are self-weighting.

Inside each sampled cluster (zip code area), a starting point is chosen randomly.

4. Background information

Clusters (zip codes) were sampled with Visual Basic –programmed MS Excel –application.

The sample was prepared in cooperation with Dr. Manninen, Professor of Statistics at University of Tampere .

 

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Last updated: 6 September 2005
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