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Variables Soodeh Arabnejad KMUPRESS, KMU

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Review of Terms Sample / Individual: The objects described by a set of data, individuals may be people, animals or things Sample / Individual: The objects described by a set of data, individuals may be people, animals or things Ex: Students, Patients, Mice Ex: Students, Patients, Mice Variable: any characteristic of an individual. A variable can take on different values for different individuals Variable: any characteristic of an individual. A variable can take on different values for different individuals Ex: Heights of individuals: Ex: Heights of individuals: Student #1: 184cm Student #2: 171cm Student #3: 171.5cm Student #1: 184cm Student #2: 171cm Student #3: 171.5cm

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Types of Variables Categorical, Qualitative or Discrete Categorical, Qualitative or Discrete Nominal Nominal Ordinal Ordinal Continuous or Quantitative Continuous or Quantitative

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Types of Variables Nominal Nominal objects or people are categorized according to some criterion objects or people are categorized according to some criterion do not imply an ordering do not imply an ordering Records which of several groups or categories to which an individual belongs Records which of several groups or categories to which an individual belongs If there are only 2 possible categories, the variable is called binary / Dichotomous If there are only 2 possible categories, the variable is called binary / Dichotomous Ex: Ex: Gender Gender Race Race Marital status Marital status Job Job

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Types of Variables Ordinal Ordinal Categories which are ranked according to characteristics Categories which are ranked according to characteristics Imply an ordering Imply an ordering Records which of several groups or categories to which an individual belongs Records which of several groups or categories to which an individual belongs Ex: Ex: SES (socio-economic status) SES (socio-economic status) Cancer Staging Cancer Staging Age group Age group Education Education

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Types of Variables Continuous or Quantitative: Continuous or Quantitative: Variables that are measured in terms of numbers Variables that are measured in terms of numbers. Numeric value that it makes sense to do arithmetic operations (+, -, x, /) Numeric value that it makes sense to do arithmetic operations (+, -, x, /) Finding an arithmetic “average” makes sense Finding an arithmetic “average” makes sense EX: EX: Height Height Weight Weight Age Age Income Income

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Caution!!! Most quantitative variables can be asked in such a way as to make them a categorical variable. Most quantitative variables can be asked in such a way as to make them a categorical variable. Ex: Age: Ex: Age: Please choose the category that describes how old you are Please choose the category that describes how old you are 0-1920-39 40-59 60-79 OVER 80 0-1920-39 40-59 60-79 OVER 80

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Kind (Role) of variables Kind (Role) of variables Independent Variable : Independent Variable : something that is changed by the scientist What is tested What is manipulated Ex: the effect of smoking on LBW Ex: the effect of smoking on LBW Dependent variable : Dependent variable : something that might be affected by the change in the independent variable What is observed What is measured The data collected during the investigation Ex: Low SES and Smoking Ex: Low SES and Smoking Confounding Confounding

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Confounding Opium MI SMK

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Determine if the variable is Quantitative or Categorical Whether or not the individual went to sleep before 12:00am Month of birth Distance from home Whether the individual has a cell phone How many e-mail messages a person has sent in the last 24 hours The age of a bride on her wedding day Whether the bride is older, younger, or the same age as the groom in a wedding couple Check your answers on the next slide

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Quantitative Variables Distance from home How many e-mail messages a person has sent in the last 24 hours The age of a bride on her wedding day Categorical Whether or not the individual went to sleep before 12:00am Month of birth Whether the individual has a cell phone Whether the bride is older, younger, or the same age as the groom in a wedding couple

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Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley Chapter 2 Data.

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