How do you determine possible sources of bias?
Determine the bias in these two situations:
i) A survey asks 500 americans in each state on what religious beleifs they possess.
ii) A food survey studying obesity is having their survey conducted near fast food resteraunts.
(i) The largest source of bias is asking the same number of Americans in each state. The result will give too much weight to states with small populations. (e.g. 500 people out of South Dakota with a population under 1 million compared to 500 people from California.)
Another possible source of bias is that some states have larger populations that conform to one religion -- for example Utah has a large Mormon population, etc...
(ii) People habituating fast food restaurants would seem to be more prone to obesity than people who do not frequent these establishments. ( Portions are large; fat and salt content are higher, etc...) This could be considered a convenience sample -- it is certainly not a random sample of the population since anyone who doesn't go to fast food places willnot be interviewed.