Lecture2 - sampling Flashcards
describe the differences between a population and an individual
An individual animal either has the disease or not, whereas in a population animals with or without the disease may be present
also
an individual animal shows certain signs of the disease, whereas in a population these signs may differ between animals
Prevalence and distribution are characteristics of …?
These characteristics cannot be established by examining …?
the population
an individual animal
define sampling
method to collect information about a subset of the population to make inferences about the characteristics of that population
why would you choose to sample over running a census?
census can be: costly, take forever, unfeasible, may contain irrelevant differences
a sample can: generate results faster, data less expensive to collect, sample results may be more accurate as it is possible to make more efficient use of resources
define target population
population to which the study results are to be extrapolated
define source population
the immediate population for which the study conclusions are to be used and from which the subset is to be selected
define sampling frame
lists all sampling units in the source population
define sampling units
individual members of the sampling frame
define internal validity
describes the relationship between study and source populations
define external validity
describes the relationship between the source and target populations
draw flow chart with terminology used in sampling process
fig 7.1 text book or lecture slide 22
Sampling design has 2 factors, what are they and what do they imply?
methodology (bias)
sample sizes - statistical inference (precision)
What are the general considerations for a study design? use injuries of working dogs in Aus as eg
- state objectives clearly and concisely
eg. estimation of the prevalence of injuries in working dogs in Australia - Define the target population
eg. All working dogs in Australia - Define the study population
eg. All working dogs on farms in the Riverina
what are the main types of sampling?
Non-probability sampling
Probability sampling
define non-probability sampling
not based on random sampling techniques