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# Hand-out%202 - . A quantitative random variable is said to...

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Graphical representation of sample data There are two main types of ‘plots’: . the data plots , for which only the data are needed – the line chart (in time), the 2-D plots (in space), and the biplot or scattergram are members of this family; . the frequency plots , for which frequencies need to be calculated (see hereafter) – the pie chart, the bar chart, the histogram, and the frequency polygon are members of that other family, in addition to the frequency table. Complement to first lecture There are two main types of random variables/sample data: . qualitative (characters); . quantitative (numbers). There is a subdivision among the quantitative random variables/sample data. . A quantitative random variable is said to be discrete when the number of its possible values is (i) finite or (ii) infinite and countable (integers or fractions).

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Unformatted text preview: . A quantitative random variable is said to be continuous when the number of its possible values is infinite and uncountable (real numbers). Notations . random variables (capitals): X , Y , Z , … . observed value of random variables (small letters): x , y , z , … . individuals: i , j , … or 1, …, n For a given random variable X , . random sample of size n : X 1 , …, X n . individual observations: x i , x j , … or x 1 , …, x n Key message The nature of a random variable (i.e., qualitative or discrete quantitative versus continuous quantitative) directs the drawing of frequency plots from sample data. Frequency classes need to be defined by the data analyst in the continuous quantitative case! Why? … Notes Frequencies or counts add up to n , the sample size. Relative frequencies add up to 1.0 or 100%! Why? …...
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## This note was uploaded on 04/18/2008 for the course AEMA 310 taught by Professor Dutieulle during the Spring '08 term at McGill.

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Hand-out%202 - . A quantitative random variable is said to...

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