ch2 - Ch 2 TheGraphicalRepresentation ofData

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1 Ch 2 The Graphical Representation  of Data variable , usually denoted with a capital letter, say X, Y, or Z, is  some characteristic of a population or a sample of interest. For  example, students’ grades. The  values   of the variable are the range of possible values for a  variable, say, students’ marks could range from 0 to 100. And,  data  are the  observed values  of a variable, for example,  student marks {67, 74, 71, 83, 93, 55, 48, …}.
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2 Types of Variables
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3 Types of Data Cardinal data  ( interval   data and ratio data are real numbers, e.g.  heights, weights, prices, etc, which are also referred to as  quantitative   or  numerical . Arithmetic operations can be performed on interval data,  thus its meaningful to talk about (2  x  Height), or (Price + Baht1000),  etc. Ordinal   data  are values which only  order  or  ranking  is meaningful, e.g.  a college course rating system as follows: {poor = 1, fair = 2, good = 3,  very good = 4, excellent = 5}. Arithmetic operations usually don’t  make any sense (Does 2  x  fair = very good?!). However, order is  maintained no matter what numeric values are assigned to each  category. That is  excellent > poor , or  fair < very good etc. Nominal data , also known as  qualitative  or  categorical  data, have  arbitrary values attached to categories of interest. For example,  responses to questions about marital status can be  coded  as: {Single =  1, Married = 2, Divorced = 3, Widowed = 4}. Because the numbers are 
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4 Data:
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5 It’s all the same  information , (based on the same  data ).
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ch2 - Ch 2 TheGraphicalRepresentation ofData

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