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2.1 Definition of target population and sampling

2.1.1 Target population

Level 1

The definition of the target population needs to be given in the report. This definition should include the geographical area (country, region, town, etc.) covered by the target population as well as the age group and gender.  It is also important to specify the exclusion of any population subgroups, such as certain ethnic groups, non-citizens or those who do not speak some major languages of the country. (See Example 2.1.1.)

EXAMPLE 2.1.1 Target population of Finnish risk factor survey in 1992. Level 1 information. 

Population

A random sample of the adult population (25-64 years of age) was studied in three areas of Finland In 1992:

map of Finland

Population size

The total population of age group 25-64 in these three areas was 340 000.

Survey organizer

Survey was organized and conducted by National Public Health Institute, Helsinki.

Level 2

The Level 2 reporting should describe in more detail the representativeness of the results. Response rates help to see if the proportion of the sample that participated to the survey is high enough to give reliable representation of the target population. (See Example 2.1.2.)

EXAMPLE 2.1.2  Target population in Finnish risk factor survey in 1992. Additional, Level 2 information.

Response rates

The over all response rate in 35-64 years old men and women was 80 %. It was 81 % in Kuopio Province, 77 % in North Karelia and 82 % in Turku/Loimaa.

Level 3

The Level 3 should report the details that may be relevant for thorough investigation of the results. To facilitate this,  information on population distribution and response rates by smaller area, age group and gender is useful. If the data are reported by socio-economic status, also information about socio-economic distribution of population are needed.  (See Example 2.1.3.)

EXAMPLE 2.1.3 Target population in Finnish risk factor survey in 1992. Detailed, Level 3 information.

Population size

The population distribution in 1992 by area, age group and gender was:

Kuopio province North Karelia Turku/Loimaa
Age group Men Women
25-34 19382 18074
35-44 22390 19923
45-54 15970 15245
55-64 13112 14272
Age group Men Women
25-34 12834 11898
35-44 15664 13473
45-54 10960 10031
55-64 9066 9703
Age group Men Women
25-34 15550 15347
35-44 15585 15615
45-54 12864 13124
55-64 9856 11721

Response rates

Response rate (%) is a number of persons participating to the survey divided by eligible sample size. The response rates by area, age group and gender in 1992 were:

Kuopio province North Karelia Turku/Loimaa
Age group Men Women
25-34 71 83
35-44 69 84
45-54 81 84
55-64 82 84
35-64* 77 84
Age group Men Women
25-34 58 73
35-44 69 79
45-54 72 85
55-64 74 87
35-64* 72 83
Age group Men Women
25-34 69 77
35-44 72 85
45-54 76 86
55-64 85 86
35-64* 78 86

* Age standardized to the Word population by 10-year age groups with weights 12, 11 and 8 (1).

2.1.2 Sampling

Level 1

For Level 1 no other information than the sample size is needed. (See Example 2.1.4.)

EXAMPLE 2.1.4 Sampling in Finnish risk factor survey in 1992. Level 1 information.

Sample size

The total eligible sample size was 5 917. 

Level 2

For Level 2, additional to Level 1 information, basic information about the sampling frame should be provided. (See Example 2.1.5.)

EXAMPLE 2.1.5 Sampling in Finnish risk factor survey in 1992. Additional, Level 2 information.

Sampling frame

The sampling frame was the national population register (http://www.vaestorekisterikeskus.fi/prc.htm) which includes all the residents of the country and which is updated continuously.

Level 3

Level 3 should report the detailed sampling information. Additionally to previous levels, the sampling method should be described. (See Example 2.1.6.)

EXAMPLE 2.1.6 Sampling in Finnish risk factor survey in 1992. Detailed, Level 3 information.

Sample size

The eligibility of the person to the sample was defined at the time of survey. The individual selected to the original sample was eligible if he/she still lived in the survey area and was alive during the time of survey examination.

The eligible sample size by area, age group and gender were:

Kuopio province North Karelia Turku/Loimaa
Age group Men Women
25-34 244 243
35-44 249 249
45-54 248 250
55-64 249 249
Age group Men Women
25-34 236 243
35-44 246 242
45-54 245 246
55-64 243 246
Age group Men Women
25-34 248 248
35-44 248 249
45-54 249 249
55-64 249 249

Sampling methods

In each area, simple random sampling, stratified by sex and 10-year age group, was used. No population groups were excluded from the sample.

References

  1. Waterhouse J, Muir CS, Correa P, Powell J (eds.) Cancer incidence in five continents. Lyon, IARC, 1976 (Vol. 3, pl 456)

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