2. Definition of Terms
•Sampling is the process of selecting a
representative group from the population
under study.
•The target population is the total group of
individuals from which the sample might be
drawn.
3.
4. Definition of Terms
• A sample is the group of people who take part
in the investigation. The people who take part
are referred to as “participants” or respondents.
• Generalisability refers to the extent to which
we can apply the findings of our research to the
target population we are interested in.
5.
6. Purpose of Sampling
• In research we are interested in learning about
large groups of people who all have something in
common. We call the group that we are interested
in studying our 'target population’.
• The target population might be as broad as all
humans, but in other types of research the target
population might be a smaller group such as
teenagers, pre-school children or people who
misuse drugs.
7. Purpose of Sampling
• It is more or less impossible to study every single
person in a target population so we select a sample or
sub-group of the population that is likely to be
representative of the target population we are interested
in.
• This is important because we want to generalize from
the sample to target population. The more
representative the sample, the more confident the
researcher can be that the results can be generalized to
the target population.
8. Sampling Bias
•One of the problems that can occur when
selecting a sample from a target population
is sampling bias. Sampling bias refers to
situations where the sample does not
reflect the characteristics of the target
population.
10. •There are various sampling methods.
The one chosen will depend on a
number of factors (such as time,
money etc.).
11. How many participants should be used?
• This depends on several factors; the size of the target
population is important. If the target population is very large
(e.g. all 4-6 yr olds in Guangdong) then you need a fairly large
sample in order to be representative.
• If the target population is much smaller, then the sample can be
smaller but still be representative. There must be enough
participants to make the sample representative of the target
population.
• Lastly, the sample must not be so large that the study takes too
long or is too expensive!
13. Instrument Development
Step 1: Choice of measurement method (e.g.
questionnaire/physical test, Interview, Observation, etc)
• For example, physical functioning can be measured with a
performance test, observations, or with an interview or self-report
questionnaire. With a performance test for physical functioning,
information is obtained about what a person can do, while by
interview or self-report questionnaire information is obtained
about what a person perceives he/she can do.
14. Instrument Development
Step 2: Selecting and formulating items
• To get input for formulating items for a multi-item questionnaire
you could examine similar existing instruments from the literature
that measure a similar construct, e.g. for different target
population, and talk to experts (both clinicians and patients) using
in-depth interview techniques.
15. Instrument Development
Step 3: Selecting and formulating items
• In addition, you should pay careful attention to the formulation of
response options, instructions, and choosing an appropriate
recall period (Van den Brink & Mellenbergh, 1998).
16. Instrument Development
Step 4: Pilot study/try out/validate
• Be aware that the first version of the instrument you develop will
(probably) not be the final version. It is sensible to (regularly) test
your instrument in small groups of people.
• A pilot test is intended to test the comprehensibility, relevance,
and acceptability and feasibility of your measurement instrument.
• From the pilot testing, you will include their (from the small group)
suggestions to improve the questionnaire
17. Instrument Development
Step 5: Field-testing
Step 6: Administration of the survey
instrument (data - gathering procedure)
31. Good Hypothesis
There are two criteria for good hypotheses.
• One, hypotheses are statements about relationships
between variables.
• Two, hypotheses carry clear implications for testing the stated
relationships.
• These criteria mean, then, that hypothesis statements contain
two or more variables that are measurable or potentially
measurable and that they specify how the variables are related.
34. Research without hypotheses
• In exploratory research our base knowledge of a subject may be so
low that we cannot formulate meaningful hypotheses.
• Nonetheless, exploratory research should be guided by a clear sense
of purpose.
• Instead of hypotheses, the design for the exploratory study
should state its purpose, or research objectives as well as criteria by
which the exploration will be judged successful.
