When making inferences from survey data we need to
distinguish between inferences that
- only want to make statements about the units in the
population from which our respondents are a sample or
- where we want to broaden the conclusions to go to wider
groups
In the first case our conclusions would only apply to the
population that existed at the time. For example, if we were
interested to know what was the total capacity of Scotland to
accommodate tourists in 2004 we might do a survey of
guesthouses and try to be estimate that fixed number.
However, as part of the same survey, we might be
interested to know whether, in the last year, guesthouses in
seaside towns had higher occupancy than those elsewhere with
a view to looking at the planning of guest house
accommodation in future. In this case our inferences would
need to go beyond the current sample and to look to predict
trends for the future. In this case we would not be
interested in exactly what had happened in the last year but
we would want to know about the underlying mechanism or model
might be producing these figures.
In the first of these examples we would be more interested
in making inferences for the current finite population but in
the second we can be thinking of our sample as generalising
more widely to a typical guest house that might be running in
Scotland this year or in future years.
It is only for the first kind of fixed population
inference that it is appropriate to make the finite sample
corrections that we will be discussing in the next
section.