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Stats Notes For Exam 1

# Stats Notes For Exam 1 - Statistics 227 Notes Ch 1 Basics...

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Statistics 227 Notes Ch. 1 - Basics Online Notes o Individuals: objects described by a set of data o Variable: any characteristic of an individual o Ask questions when exploring data: Who are the individuals? What and how many variables are there? What purpose does the data have? o Categorical variable: places an individual into 1+ groups or categories o Quantitative variable: takes numerical values for which arithmetic operations make sense; usually recorded in a unit of measurement o Exploratory data analysis: use of graphs and numerical summaries to describe the variables in a data set and the relations among them o EXPLORING DATA 1. Begin by examining each variable by itself. Then move on to study the relationships among the variables. 2. Begin with a graph or graphs. Then add numerical summaries of specific aspects of the data. o DISTRIBUTION OF A VARIABLE Distribution of a variable tells us what values it takes and how often it takes these values. Distribution of a categorical variable lists the categories and gives either the count or the percent of individuals who fall in each category. o EXAMINING A HISTOGRAM In any graph of data, look for the overall pattern and for striking deviations from that pattern. You can describe the overall pattern of a histogram by its shape, center, and spread. An important kind of deviation is an outlier, an individual value that falls outside the overall pattern. o SYMMETRIC AND SKEWED DISTRIBUTIONS A distribution is symmetric if the right and left sides of the histogram are approximately mirror images of each other. A distribution is skewed to the right if the right side of the histogram (containing the half of the observations with larger values) extends much farther out than the left side. It is skewed to the left if the left side of the histogram extends much farther out than the right side. o Other methods of displaying data: 1) stem plots 2) time plots : plots each observation against the time at which it was measured 1

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Statistics 227 Notes Class Notes – 8/29/07 o Descriptive statistics : extract or recapitulate the info content; kernel of important info is available at a glance o Inferential statistics : produce valid conclusions o Unemployment rate : % of labor force who are not employed for pay o Labor force : all those over 16 who’re either employed, actively seeking work, or awaiting recall from layoff o Condensed array (sort) : It is an arrangement of the data from lowest to highest. Frequency distribution : It is a condensed array or sort of the data. 1) class intervals (bins) 2) count up the observations in the bins Bins Frequency 3.0 – 3.9 4 4.0 – 4.9 3 5.0 – 5.9 11 6.0 – 6.9 3 7.0 – 7.9 7 8.0 – 8.9 1 9.0 – 9.9 2 o Distribution: includes uniform (looks like a rectangle) Ch. 2 - Distributions Online Notes o Mean : ordinary arithmetic average (x bar) To find the mean: Compact notation: o Median : midpoint of a distribution (M) To find the median of a distribution: 1. Arrange all observations in order of size, from smallest to largest.
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Stats Notes For Exam 1 - Statistics 227 Notes Ch 1 Basics...

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