AS Level Statistics: Sampling
Definitions
1. Census – A survey that involves all the population.
2. Sample – A small section of a population that is chosen for the survey.
Advantages and disadvantages
Census Sample
Adv. Adv.
• Accurate information • Faster and cheaper than a census.
• Does not introduce bias. • Easier.
Disadv. Disadv.
• Can be time consuming. • Each sample will give different
• Expensive. results which causes a variation
• Difficult to ensure everyone is between samples.
surveyed. • Very easy to introduce bias.
Sampling Techniques
These are the methods by which a representative sample is chosen from a
population. There are six of them.
1. Random Sampling
o Each member of the sample frame has an equal chance of being
selected.
o One way of doing this is to assign each member of the sample frame a
number. Random numbers are then generated (using a computer or from
a table) and the members whose numbers come out are sampled.
o An advantage of this is that it is completely unbiased.
o However, a disadvantage of it is that the sample might not be very
representative of the population.
2. Systematic Sampling
o Selects every nth member of a population.
o The advantage of this method is that it does not involve random
elements, so can be done faster with a machine.
Definitions
1. Census – A survey that involves all the population.
2. Sample – A small section of a population that is chosen for the survey.
Advantages and disadvantages
Census Sample
Adv. Adv.
• Accurate information • Faster and cheaper than a census.
• Does not introduce bias. • Easier.
Disadv. Disadv.
• Can be time consuming. • Each sample will give different
• Expensive. results which causes a variation
• Difficult to ensure everyone is between samples.
surveyed. • Very easy to introduce bias.
Sampling Techniques
These are the methods by which a representative sample is chosen from a
population. There are six of them.
1. Random Sampling
o Each member of the sample frame has an equal chance of being
selected.
o One way of doing this is to assign each member of the sample frame a
number. Random numbers are then generated (using a computer or from
a table) and the members whose numbers come out are sampled.
o An advantage of this is that it is completely unbiased.
o However, a disadvantage of it is that the sample might not be very
representative of the population.
2. Systematic Sampling
o Selects every nth member of a population.
o The advantage of this method is that it does not involve random
elements, so can be done faster with a machine.
