chap2 - Chap 2: Description of Populations and Samples...

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1 1 Chap 2: Description of Populations and Samples (STAT 350) Chapter 2 2 Review of Lecture 1 z Introduction to Statistics coverage: chap 1 + additional materials 1.1. Variation in data: (motivation) One group, two groups 1.2. What is statistics? What does it do? (its role in science) 1.3. Key ideas in statistical reasoning. Coin example, idea Study design Æ Stat. analysis z Statistical Language - coverage: chap 2.1 2.1, Variable and notation 2.2, Measurement scale
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2 3 Objective of Exploratory Data Analysis Why we need to organize our data? z Condense data and present it in a manageable form z Look at detailed distributions (shape, center, spread) before computing summary measures or performing statistics z Gain insight into the nature of the data set z Look for errors, abnormal points 4 Outline of Chap 2 How to organize your data? 2.1 Frequency Plots: Bar chart (categorical data) Dotplot (quantitative data) Stem-and-Leaf Diagrams Histogram 2.2 Summarizing your data: Shapes of Frequency Distribution Measure of Center Boxplot , Percentiles Measure of Dispersion (how spread is your data)
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3 5 2.1.1 Bar chart –for categorical variable (textbook, eg. 2.1) Æ Simple graph Show both the categories (variable value) and the number of observations in each category 6 Bar Chart – cont. z What type variable? “color of poinsettias” z The amount of space between the bars in plot matters? Frequency = the number of times that value occurs in the data Relative Frequency = frequency / n (n = total number of observations, sample size) Percent frequency = Relative Freq * 100%
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chap2 - Chap 2: Description of Populations and Samples...

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