APPLIED YEAR 1- Data Handling

Population

The entire set of items (sampling units) in the group being studied

Sample

A selection from the population

Advantages of sample

Cheaper, quicker

Disadvantages of sample

Data may not be accurate, Data may not be large enough to reflect sub-groups

Sampling unit

A member from the population

Sampling frame

List of all the sampling units

Census

Taking data from every member of a population

Advantages of census

Accurate

Disadvantages of census

Expensive, some testing destroys the item

Simple random sampling

1. Each member of the population (sampling units) is given a unique number 2. Random number generator to select sample 3. Each member of the population (sampling unit) has an equal chance of being selected

Avantages of simple random sampling

Bias free, Easy/cheap

Disadvantages of Simple random sampling

Sampling frame required

SystematiK random sampling

K =. Sampling interval - population size/sample size.

1. Number population 2. Choose random starting point between 1-k 3. Select every kth item

Advantages of systematic random sampling

Simple/quick

Disadvantages of systematic random sampling

Sampling frame required

Stratified random sampling

1. Divide population into strata (groups) 2. Work out how many to sample from each strata (eg. ratio of girls to boys in entire population should mirror number of strata girls and strata boys) 3. Carry out simple random sample on each strata

Advantages of systematic random sampling

Accurately reflects population

Disadvantages of stratified random sampling

Need clear strata for population, selection within each strata requires a sampling frame

IF SAMPLING FRAM REQUIRED

Random sampling

Opportunity sampling

Take sample from who/what is available

Advantage of Opportunity sampling

Easy/cheap

Disadvantage of opportunity sampling

Unlikely to be representative of the whole population

Quota sampling

Similar to stratified sampling, quotas (groups) chosen out of population, taking into account ratio compared to entire population. However members to go within groups are not selected randomly, they are filled by opportunity sampling.

Advantage of quota sampling

No sampling frame needed

Disadvantage of quota sampling

Not random, bias

Qualitative data

No numerical data

Quantitative data

Numerical data

Discrete

Can only take certain values (eg. Shoe size)

Continuous

Can take any value in a range, including decimals (eg. Height)