Vinnumarkaður - 01.09.1996, Blaðsíða 26

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Synopsis of methods and concepts
3. Synopsis of Methods and Concepts
Part 3.1 of this synopsis deals with the Icelandic Labour Force
Survey (ILFS), its methods, reliability and principal con-
cepts. Other data sources are described in a similar manner in
parts 3.2-3.5.
3.1 The Icelandic Labour F orce Survey
3.1.1. Previous labour force statistics
The principal source for labour force statistics in Iceland has
for a long time been based on information on working weeks
derived from tax returns as well as the official registration of
unemployment. These data, however, have many shortcom-
ings, e.g., little possibility of anaiysis according to various
socio-economic groups, lack of important variables such as
working hours and status in employment, and lack of inter-
national comparability.
For these reasons Statistic Iceland (SI) decided to start its
own labour force survey in 1991 based on intemational
recommendations. The first such survey was conducted in
April 1991 and since the survey has been conducted twice a
year, in April and November.
3.1.2. Execution
Questionnaire. The ILFS questionnaire is based on compa-
rable questionnaires used in the Nordic countries. The ques-
tionnaire has also been developed so that standardised data can
be sent to Eurostat according to the EEA agreement. Ques-
tions of particular national interest have also been included.
In the course of the first three years of the ILFS the
questionnaire has changed considerably, even though the main
core of questions has remained the same. Many questions
have been added, some have been discarded while others have
been rephrased.
Survey periods and number of interviewers. Each sur-
vey has one reference week. As each survey is conducted for
10-11 days, the reference week is moved forward after the
seventh day for the remaining respondents (Table 2.1).
Usually the first reference week is the first or second week of
the interview month.
From November 1991 interviewers have been hired from
outside the SI. For the most part the interviewers have had
previous experience in working with telephone surveys. Each
survey is conducted by approximately 20 interviewers. Be-
fore each survey the interviewers are trained in conducting
interviews and working with the computer aided interviewing
system.
Data gathering. All interviews in the ILFS are telephone
interviews. Most interviews take place in the evenings and
during weekends, except for interviews by appointment
during normal working hours. Telephone numbers for re-
spondents are provided by the Post and Telecommunication
Administration. Considerable effort is made to reach partici-
pants who have moved or do not have a telephone. No
participant is visited, however.
In No vember 1992 computer aided telephone interviewing
(CATI) was introduced, using the Dutch program BLAISE.
This has proved to save both time and effort as well as reducing
interviewererrors. InNovember 1992 and April 1993 answers
to open questions about economic activity and occupation
continued to be handwritten but since November 1993 all
responses have been entered immediately into a computer by
the interviewers.
Sample and response. The sampling frame for the ILFS
is drawn from all persons in the National Register who are 16-
74 years of age and with domicile in Iceland at the time of the
survey. Icelandic persons who are students outside
Scandinavian countries are allowed to retain their domicile in
Iceland, whereas students in other Nordic countries are
required by Nordic agreements to transfer their registration to
the respective country. In order to treat both groups of
students in the same manner, all persons who reside abroad
for more than 6 months are defined as ineligible in the final
sampling frame. This differs somewhat from international
recommendations where all students abroad are considered as
part of the population, irrespective of length of study.
The sample is a rotating panel sample of approximately
4.400 individuals selected by simple random sampling with-
out replacement from the sampling frame. The sample is
divided into four rotation groups of approx. 1.100 individuals,
each of which participates in four successive surveys. The
sample units are returned to the sampling frame when four
years have elapsed from their first being selected.
From November 1994 the sampling frame was extended to
persons 14 years of age who will reach 16 years by the time
the fourth successive survey will be conducted. The size of
the rotation group was also increased to 1,140 individuals.
Persons younger than 16 years of age are subsequently
introduced into the sample when they reach the lower age
limit. This ensures that 16 and 17 year age groups will alway s
be proportionately represented.
In the second to fifth surveys sampled individuals who had
previously refused to answer or were not able to participate
due to illness or disability were not contacted again. The
number of people contacted was thus smaller than the actual
sample. In November 1993 refusers (from earlier surveys)
were recontacted. Of these 37% refused again, 52% re-
sponded. 7 % were not at home and 4% were unable to ans wer
due to illness or disability. In 1994 and 1995 this effort of
refusal conversion was continued, albeit with less success. As
a result, the net non-response has been reduced to less than
10% of the sample (cf. Table 2.2).
3.1.3. Reliability
Errors in a sample survey fall roughly into two categories:
Sampling errors and non-sampling errors. This section deals
mostly with the errors that have affected the ILFS and is not
a comprehensive discussion of errors in sample surveys.
Sampling errors. Every sample incurs uncertainty due to
the method of sampling. Because of the random nature of this
uncertainty, it is possible to calculate the confidence limits for
the estimates. These are shown in Table 2.3 for the 95%
confidence level. If, e.g., the mean number of unemployed in
the year 1995 is estimated as 7,200, the confidence limit for
the number which comes nearest to this estimation is ± 1,000.