STATISTICS CH.1

population

the whole set of items that are of interest

census

observes or measures every member of a population

sample

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

census advantage

it should give a completely accurate result

census disadvantages

1. time consuming and expensive

2. cannot be used when the testing process destroys the item

3. hard to process large quantity of data

sample advantages

1. less time consuming and expensive than a census

2. fewer people have to respond

   1. less data to process than in a census

sample disadvantages

1. data may not be as accurate

2. sample may not be large enough to give information about small sub-groups of the population

sampling units

individual units of a population

sampling frame

sampling units of a population that are individually named / numbered to form a list

random sampling

every member of the population has an equal chance of being selected (representative of pop. and removes bias)

what are the 3 methods of random sampling?

1. simple random sampling

2. systematic sampling

3. stratified sampling

simple random sampling

every sample of size n has an equal chance of being selected

what are the 2 methods of choosing the numbers for simple random sampling?

1. generating random numbers (e.g. a calculator)

2. lottery sampling (e.g. pick numbers from a hat)

systematic sampling

the required elements are chosen at regular intervals from an ordered list

stratified sampling

population is divided into mutually exclusive strata (e.g. males and females) and a random sample is taken from each

pros and cons of simple random sampling

pros and cons of systematic sampling

pros and cons of stratified sampling

what are the 2 types of non-random sampling?

quota and opportunity sampling

quota sampling

researcher selects a sample that reflects the characteristics of the whole population

opportunity sampling

takes the sample from those available at the time and fit the criteria

quota pros and cons

opportunity pros and cons

what are the 4 data types?

1. qualitative

2. quantitative

3. discrete

4. continuous

qualitative

non-numerical data

quantitative

numerical

discrete

can only take certain values (often integers)

continuous

can take any value in a range, must be grouped