Edexcel A Level Maths Year 1 Applied Chapter 1

Sample

A selection of observations taken from a subset of the whole population which is used to find out information about the population as a whole.

Census Adv / Disadv

- It should give a completely accurate result. - Time consuming & expensive. - Cannot be used in cases were testing will destroy the sampling units. - Harder to process large quantity of data.

Sample Adv / Disadv

- Less time consuming & expensive than census. - Fewer respondents needed. - Less data to process makes it easier. - The data may not be as accurate as a census (owing to bias). - The sample may not be large enough to give information about small subgroups of th population.

Sampling units

Individual members of the population

Sampling frame

A named or numbered list of all the members of the sampling units (like a register or electoral roll).

Random Sampling

Every member of the population has an equal chance of being selected, and so the sample ought to be representative of the population and less likely to be biased.

Simple random sampling

This type of sampling requires a sampling frame. It can be carried out by two methods - lottery or generating random numbers using a calculator or computer.

Systematic Sampling

The required elements of the sample are chosen at regular intervals from an ordered list. The first sampling unit is selected at random.

Stratified Sampling

The population is divided into mutually exclusive strata (groups) and a random sample is taken from each, in proportion with the population.

Simple random sampling Adv/Disadv

- free of bias. - easy and cheap for small populations and samples. - each samplng unit has a known and equal chance of selection. - not suitable for large populations or samples. - A sampling frame is needed.

Systematic Sampling Adv/Disadv

-simple and quick. - Suitable for large samples and populations. - A sampling frame is needed. - It could introduce bias if the sampling frame is not random.

Stratified Sampling Adv/Disadv

-the sample accurately reflects the population. - Guarantees the proportional representation of groups within a population. - Population must be clearly classified into distinct strat. - Selection within each category suffers from the same disadvantages as simple random sampling.

Quota sampling

- An interviewer or researcher selects a sample that reflects the characteristics of the whole population.

Opportunity sampling

This sample is from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Quota sampling adv/disadv

- Allows a small sample to be still be representative of a population. - No sampling frame required. - Quick, easy and inexpensive. - Allows for easy comparison between different groups within a population. - Non-random sampling can introduce bias. - Population must be divided into groups, which can be costly or inaccurate. - Increasing scope of a study increases the number of groups which adds time and expense. - Non-responses are not recorded as such.

Opportunity sampling Adv/Disadv

- Easy to carry out. - Inexpensive. - Unlikely to provide a representative sample. - Highly dependent on individual researcher.

Quantitative Variables

Variables or data associated with numerical observations.

Qualitative Variables

Variables or data associated with non-numerical observations.

Continuous Variables

Data which can take any value in a given range.

Discrete Variables.

Data which can only take particular values in a given range.