MATH1005 STATISTICS M.Harahap@maths.usyd.edu.au Mahrita Harahap Tutorial 2: Numerical Summaries and Boxplot

In statistics we usually want to statistically analyse a population but collecting data for the whole population is usually impractical, expensive and unavailable. That is why we collect samples from the population (sampling) and make inferences about the population parameters using the statistics of the sample (inferencing) with some level of accuracy (confidence level). A population is a collection of all possible individuals, objects, or measurements of interest. A sample is a subset of the population of interest.

Population vs. Sample

Population vs. Sample

MEASURES OF CENTRAL TENDENCY: The mean is the average of a set of numbers. > Affected by each value in the data set including extreme values. The mean is helpful for data which is basically symmetric which not too many outliers, and for theoretical analysis. The median is the middle value of a set of numbers after they have been arranged in an order. > Unaffected by extremely large and extremely small values. The median is robust which means it is not aected by some extreme readings. This makes the median preferable for data which is skewed or has many outliers (eg Sydney house prices).