handout240.2

# handout240.2 - Stat240 Describing Data by Tables and...

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1 Stat240. Describing Data by Tables and Graphs. (Chapter 2, sects 1, 2, 3). Handout 2 some good Stats Links: http://www.learner.org/exhibits/statistics/ Gallup - http://www.gallup.com/ - the famous polling company Some Terminology Variable : a characteristic which varies over time or in different individuals/objects. – Response of a student. (Age, height, religious affiliation, social class). Population : the whole set of units on which some feature is investigated. – American registered voters. The set of students. Sample : a subset of the population. – In the poll example, the set of students who were interviewed. Sample/experimental unit : the unit on which measurements are taken. – The individuals selected to be interviewed. – The individuals selected for an experiment. Sample size : the number of sample/experimental units. •A measurement results when a variable is actually measured on an experimental unit. A set of measurements is called data. Example 2.1 Student GPA Gender Year Major Units Enrolled 1 2 F Fr Psychology 16 2 2.3 F So Maths 15 3 2.9 M So English 17 4 2.7 M Fr English 15 52 . 6 F J r B u s i n e s s 1 4 A sample of n = 500 students was selected from all undergraduates at a large university to investigate gender and major distribution How many variables have you measured? Univariate data: One variable is measured on a single experimental unit. Bivariate data: Two variables are measured on a single experimental unit. Multivariate data: More than two variables are measured on a single experimental unit. Types of variables and information Qualitative variables (categorical data)- measure a quality or characteristic on each experimental unit . Examples: • Make of car (Dodge, Honda, Ford…) • Gender (male, female) • Hair color (black, brown, blonde…) • State of birth (California, Arizona,….) • Data: frequency, that is the number of times a particular category is observed in the sample/population.

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2 Quantitative variables (numerical ) measure a numerical quantity on each experimental unit. 9 Discrete - if it can assume only a finite or countable number of values. 9 Continuous - if it can assume the infinitely many values corresponding to the points on a line interval. – Data: are the actual measurements. – Example: • For a particular day, the number of cars entering a college campus is measured. ( Quantitative discrete) • Time until a light bulb burns out ( Quantitative continuous) categorical Example 2.1 cont’d Student GPA Gender Year Major Units Enrolled 1 2 F Fr Psychology 16 2 2.3 F So Maths 15 32 . 9 M S oE n g l i s h 1 7 42 . 7 M F r E n g l i s h 1 5 5 2.6 F Jr Business 14 Sample units numerical numerical Sample size: n=500 Types of Variables variables Qualitative
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## This note was uploaded on 04/09/2008 for the course STAT 240 taught by Professor Jeneralczuk during the Spring '08 term at UMass (Amherst).

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handout240.2 - Stat240 Describing Data by Tables and...

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