Stats Knowledge chapters

Population

A whole set of items which are of interest

Census

Observes or measures every member of the population

Sample

A selection of observations taken from a subset of the population which is used to gather information about the whole population

Pros and Cons of a Sample

+Quicker and easier because less people have to respond and there is less data to process

-the sample may not be large enough to give information about small subsets of the population OR the population as a whole (innacurate)

Pros and Cons of a Census

+Completely accurate

-Time consuming and expensive because lots of data to process (which is hard)

Sampling units meaning

Individual units of the population

Sampling Frame

A sampling frame is defined as the source material or device from which a sample is drawn. It includes a complete list of all individuals, households, or institutions within a target population that can be sampled.

named and numbered into a list

Random Sampling types and explanations

1. Simple random(size n, everyone has the same chance of selection), Decided through RNG on calc or lottery sampling

2. Systematic damling, elements are chosen at a regular interval from a list. Take every Xth person and choose the first at random

3. Stratified Sampling divides the population into mutually exclusive Strata and random sample is taken from all (proportion same as prop in population)

Why can a sampling frame be a con

Expenive, time consuming, human error in creation, bias, innaccurate to population (bias)

Pros and Cons of simple random sampling

+cheap, easy, no bias p is same for all units

-innacurate if population is large, hard if sample is large

-needs sampling frame

Pros and Cons of systematic sampling

+quick, simple, and good for any populattion size

-sampling frame needed and may be bias if not random

Pros and Cons of stratified sampling

+reflects the population structure inculding minorities

-population has to be clearly classified into distinct strata

-sampling frame issues

Non random sampling

1. Quota sampling where researchers choose a sample which relects the characteristics of the whole population

   (div pop into groups to find the correct proportions, interview people then allocate)

2. Opportunity/ convenience is where people who are avaliable and fit the criteria are chosen.

Pros and Cons of Quota sampling

+no sampling frame so is quick, easy and inexpensive.

+can use a small sample which is representative

+allows for comparison between groups in the population

-bias if not random

-hard to divide the population (costly and innacurate)

-non responses arent recorded

Pros and Cons of opportunity sampling

+easy, quick, cheap

-unrepresentive, bias dependent on researchers