Statistics

Question 1

Examples of sampling frames

Answer 1

Local electoral roll/register(to vote locally)
Driver Vehicle Licencing Authority
School registers

Question 2

Census

Answer 2

Data collected from the entire population

Question 3

Census advantages

Answer 3

Should give completely accurate results - uses all data

Question 4

Census disadvantages

Answer 4

Time consuming and expensive
Cannot be used when testing involves destruction
Large volume of data to process
Can destroy all bulbs

Question 5

Population

Answer 5

The whole set of items that are of interest

Question 6

Sample

Answer 6

A subset of items chosen from a population/a selection of observations taken from a population

Question 7

Sampling unit

Answer 7

Each individual item in the population that can be sampled

Question 8

Sampling frame

Answer 8

A list where sampling units of a population are individually named or numbered

Question 9

Sample advantages

Answer 9

Less expensive
Less time consuming
Less data to process

Question 10

Sample disadvantages

Answer 10

Data may not be representative of population

Question 11

Random sampling metjod

Answer 11

1. Need a sampling frame(put the population into an ordered list).
2. Each item is assigned a different number from 1 to N(population size). Use a random number generator to select ‘n(size of random sample)’ unique numbers.
3. Choose the items corresponding to these numbers to form the sample.

Question 12

Advantages of random sampling

Answer 12

Bias free
Easy and cheap to implement for small populations and samples.
Each sampling unit has a known equal chance of being selected.

Question 13

Disadvantages of random sampling

Answer 13

Not suitable when population size is large
Sample may not accurately reflect the population - not accurate proportion of population
A sampling frame is needed

Question 14

Systematic sampling metjod

Answer 14

1. Need a sampling frame - ordered list.
2. Generate the number of the first item to be chosen randomly.
3. Each item is assigned at a different number from 1 to N(population size). Take every kth elements from the ordered list of population to form the sample.
4. k= pop size(N)/samp size(n)

Question 15

Advantages of systematic sampling

Answer 15

Simple and quick to use
Suitable for large samples and populations

Question 16

Disadvantages of systematic sampling

Answer 16

Can introduce bias if sampling frame is small and not random as patterns can be picked up in the data.
A sampling frame is needed.

Question 17

Advantages of stratified sampling

Answer 17

Sample accurately reflects population structure.
Guarantees proportional representation of groups within population.

Question 18

Disadvantages of stratified sampling

Answer 18

Sampling frame is needed and population must be clearly classified into distinct strata.
Selection within each stratum suffers from same disadvantages as random sampling.

Question 19

Disadvantages of electoral register

Answer 19

Doesn’t include people ineligible to vote, like this under the age of 18, and may also be incomplete since there may be residents not registered to vote

Question 20

A simple random sample

Answer 20

A simple random sample of size n is one where every sample of size n has an equal chance of being selected

Question 21

What is meant by a systematic sample

Answer 21

Here, the required elements are chosen at regular intervals from an ordered list. The first item is chosen at random

Question 22

Stratified sample

Answer 22

A sample which is proportional to the number of items in each stratum/group

Question 23

How t9 take a stratified sample

Answer 23

hDivide the sample size into the same proportion as the population/different strata, then randomly select this sample size of the population( from an ordered list)