Answer :
b) not valid because it is not a random sample
a) is biased because the first 8 people are unlikely to be representative of the population
c) is biased as offering money will influence the people who reply
d) is untrue because short studies are valid if they are representative
a) is biased because the first 8 people are unlikely to be representative of the population
c) is biased as offering money will influence the people who reply
d) is untrue because short studies are valid if they are representative