Statistics 12 Maths A

Discrete Counting Number of people (can’t have a part of person) Shoe sizes (can have half sizes, but not quarter sizes) Number of cars in a car park Continuous Measuring Time in a race Baby’s weight Length of a leaf What are the limitations with collecting continuous data?

Discrete GraphContinuous Graph

Census Census – data gathered from an entire population Examples of a census: the entire population of a country. Australians must give information about themselves every 5 years to the Australian Bureau of Statistics (next census date is August 2016) Can also conduct a census on a population of objects Example: number of wattle trees in a National Park or soil in a farmer’s field

Survey Survey – data gathered from a sample (a proportion of a the population) It is impractical to conduct a census every time data is needed so a survey is done instead.

Random Sampling Each element of the population has an equal chance of being selected Use 2, 3 or 4 digit random number tables Random function on calculator Lot sampling (lotto numbers used) Using a spreadsheet (page 176)

Accessibility sampling A sample drawn only from easily accessible items often does not represent the views of the population. Eg ask 100 four year old preschool girls if Pink is there favourite colour, then ask the same question of 100 four year old boys.

Systematic Sampling For example choose every 10 person in the school from an alphabetical list Last name on every page in a telephone directory

Quota Sampling Quota refers to a particular number of items to be surveyed Example: 1000 Brisbane residents, 500 must be female, 500 must be male. In each group 25% must be 13 – 17 years, 25% 18 – 25, 25% 26 – 35 years, 25% 36 + years. Any method of choosing each sub-group can be used Open to bias

Judgmental Sampling The person conducting the sample makes a judgment about the composition of the sample.

Stratified Sampling When a sample is selected from a population consisting of various strata, or levels, it is important to have the strata or levels in the sample occurring in the same proportions as they do in the population. Eg selecting a Student Representative Council in a school where each year level has a variation in numbers. (page 179)

Capture - Recapture Capture–recapture sampling is particularly useful for estimating populations of items that are difficult or impossible to count, such as plants and animals. It is often necessary to monitor wildlife numbers to prevent the occurrence of plagues and the extinction of species. The technique used is to capture a certain number of the species, tag them, then release them. At a later date, another sample is caught and the number of tagged specimens in the sample observed. From this information, the population of the species can be estimated.

Exercise 4B Q2 – Random numbers Q9, Q11 – strata Q12, Q13, Q17 capture-recapture