AP STATISTICS: WHY? WHO? WHAT? | SHUBLEKA
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Statistics = science of learning from data Data = numbers with a context Individuals = objects described by a set of data; may be people, animals, or things. Variable = a characteristic of an individual; it can take different values for different individuals
Categorical Variable = places an individual into one of several groups Example: math course a student is enrolled in. Quantitative Variable = takes numerical values for which arithmetic operations make sense Example: math midterm grade of a student Distribution of a Variable = tells us what values it takes and how often it takes these values Exploratory Data Analysis: 1. Examine each variable by itself 2. Study relationships among the variables 3. Construct graphs and add numerical summaries CATEGORICAL VARIABLES The distribution of a categorical variable includes the categories and the count or percent of individuals who fall in that category. • •
Bar graph – may be used to display the count of any categorical variable Pie chart ‐‐‐ percents must add to 100% so any individual may belong to exactly one category
QUANTITATIVE VARIABLES Stemplot = quick picture of the shape of the distribution 1. Separate each observation into a stem consisting of all but the final digit and a leaf, the final digit. 2. Write the stems in a vertical column in increasing order. 3. Write each leaf in the row to the right of its stem, in increasing order out from the stem. Example: Literacy Rates Histogram = breaks the range of values into classes (count or frequency VS variable values)
AP STATISTICS: WHY? WHO? WHAT? | SHUBLEKA
Example: IQ Test Scores Examining Distributions • • • • • •
overall pattern striking departures shape – center – spread outlier = an observation falling outside the overall pattern mode = peak (unimodal = one major peak) symmetric vs skewed
Examples: biological phenomena tend to have symmetric distributions; money amounts tend to have skewed distributions.