selection of participants
DESCRIPTION
Selection of participants. EHES Training Material . Who can be invited?. In principle, every person age 25 to 64 years living in the country is eligible Temporary visitors are not included in the survey. How are people selected?. Stage 1 The country is divided into examination areas - PowerPoint PPT PresentationTRANSCRIPT
Selection of participants
EHES Training Material
Who can be invited?
• In principle, every person age 25 to 64 years living in the country is eligible
• Temporary visitors are not included in the survey
How are people selected? Stage 1• The country is divided into examination areas• A number of these are selected randomly
An example country
How are people selected? Stage 2• Within each selected examination area we select
people from the population register also randomly
An example country
How are people selected? Stage 2• Within each selected examination area we select
households from a local household list also randomly
An example country
How are people selected? Stage 3• Within each selected household we select all
household members
An example country
Stage 3• Within each selected household we select
1 person
How are people selected?
An example country
What is random selection?• Selecting a person, household, dwelling or area
randomly means that they are selected entirely by chance
• We can calculate how likely someone is to be selected.
• We can not calculate if they actually will be selected – this is the random part.
Why random selection?• To estimate the health of the population we need
to know everyone’s chances of being selected/invited
• This is only possible with random selection• Replacing someone who does not want to or can
not participate with someone else means we no longer have a random sample and can not estimate health figures accurately from the data
Sample
Biased samples• A sample is biased if it does not reflect the
population and will tend to give the wrong result• Biased samples can result from:
• Samples that are not randomly taken from the population
• Low response rates among certain groups of the sample (eg. people who are not well)
Biased sample
Sample
Population Population
Representative sample Biased sample
Questions and answersThe following slides are frequently asked questions
that may come from the survey participants and which fieldwork staff should be able to answer
“Why was I selected for the survey?”
• We have drawn a random sample of people from all over the country using the population register. It is share chance that you have been selected.
“How many people have you invited to participate in this
survey?”
• We have invited 4000 people from all over the country.
”Why do you select participants at random?”
• We can’t ask everyone to participate so we invite a small fraction of the population. It is important for this group to be selected randomly so they reflect the population as a whole.
”How can you learn about the general health for the entire
country by only examining a few people?”
• It’s not feasible to interview and examine everybody in the country. Instead we randomly select a group to represent the country. This is enough for us to gauge an accurate picture of the country’s health.
“What do I get in return for participating?”
• You will receive (mention incentive and) a free health check-up
• Additionally, the information is important for research and health monitoring purposes, which are needed to plan health services and health promotion activities for future generations
”My husband/friend is participating and I would like to
too. Can I turn up?”• It’s great that you are interested in the survey but
unfortunately we can’t include you this time as we only have the resources to survey those we selected randomly to participate.
• It’s great that you are interested in the survey and you are welcome to come on (date/time). Unfortunately you won’t be included in our official data but you can still join in and receive your test results.
”I don’t mind answering some health questions but I’m not
prepared to give a blood sample so I don’t think I should
participate at all.”• It is very important for the survey that you
participate in any way you can. We can start with the questionnaire and measurements and if you want to stop there that’s fine. You can stop at any time during the survey.
Acknowledgements• Slides
• Susie Jentoft and Johan Heldal