section1-_3_slides

section1-_3_slides - STAT1008 Section 1 Variables Data and...

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1 STAT1008 Section 1 Variables, Data and Statistics – Basic Concepts What is “Statistics”? “a way to get information from data” A framework for dealing with variability A way to make decisions under uncertainty Statistical inference: the problem of determining the behaviour of a large population by studying a small sample from that population What is a population? What is a sample? Population: a collection of the whole of something – e.g. all female students of ANU; all people who live in Tuggeranong; all all people who live in Tuggeranong; all people who play the flute. Sample: a set of individuals drawn from a population e.g. the female students in STAT1008 are a sample of all female students at ANU.

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2 If we have a population…. We can get parameters – true values for things like the centre and spread of the population We know the answers – what proportion are this tall? We look at the population and get the answer. If we have a sample… We can get statistics – these are values that estimate the parameters e.g. sample centre and sample spread used to estimate and sample spread used to estimate population centre and population spread We have to use inference to do this estimation – what proportion are this tall? Based on our sample, we would expect…. So, statistical inference… The process of making an estimate, prediction or decision about a population, based on a sample. Note: populations are generally hard to study – large Note: populations are generally hard to study – large, awkward! So using samples is much more common Decisions made using samples will not always be correct: need a measure of reliability Confidence level: proportion of times that an estimating procedure will be correct Significance level: measures how many times the conclusion will be wrong