Topic_02_Chap2

# Topic_02_Chap2 - Descriptive Statistics Chapters 2 through...

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Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 1 of 55 Descriptive Statistics Chapters 2 through 4 cover Descriptive Statistics After we collect the raw data (from a sample survey or a designed experiment), we can: § Describe the data using visual methods (charts, etc.) § Describe the data using numeric methods (averages, etc.) Different methods are appropriate for different types of data. Descriptive Statistics : Statements about the Sample Focus is on interpreting and presenting the data that has been collected via the sample. No attempt is made to generalize to other (larger) groups, such as the population.

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Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 2 of 55 Chapter 2, Section 1 (Outline) Organizing Qualitative Data Organize qualitative data in tables. Construct bar graphs. Construct pie charts. Reminder: Raw qualitative data comes as a list of values … each value is one out of a set of categories . Allows researcher to categorize or classify individuals into groups.
Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 3 of 55 Frequency/Relative Frequency A frequency distribution lists: Each of the categories. The frequency, or the count, of the observations that belong to each category. A relative frequency distribution lists: Each of the categories. The relative frequency, or the proportions (or percents), of the observations out of the total that belong to each category. Counts Frequency Proportions (or Percents) Relative Frequency

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Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 4 of 55 Example Consider the following data set: blue, blue, green, red, red, blue, red, blue The frequency distribution for this qualitative data is: The most commonly occurring color is ______ Color Frequency Blue ? Green ? Red ? Frequency Table
Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 5 of 55 Example (cont.) The relative frequency distribution is computed as follows: § Sum of all frequencies = _____ § Blue has a relative frequency of __________________ § Green has a relative frequency of _________________ § Red has a relative frequency of ___________________ Color Relative Frequency Blue ? Green ? Red ? Color Relative Frequency Blue ? Green ? Red ? Proportion Percent Relative Frequency Table

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Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 6 of 55 Bar Graphs A bar graph : Lists the categories on the horizontal axis. Draws rectangles above each category where the heights are equal to the category’s frequency or relative frequency. Relative Frequency A bar graph is a "picture" of a frequency/relative frequency table for qualitative data.
Sullivan – Fundamentals of Statistics , 2nd Edition – Chapter 2 – Slide 7 of 55 Bar Graphs (cont.) Good practices in constructing bar graphs: The horizontal scale: § The categories should be equally spaced.

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## This note was uploaded on 02/14/2011 for the course STAT 250 taught by Professor Sims during the Spring '08 term at George Mason.

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Topic_02_Chap2 - Descriptive Statistics Chapters 2 through...

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