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28 Cards in this Set
- Front
- Back
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Bimodal
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Distributions with two modes
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Boxplot
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A boxplot displays the 5-number summary as a central box with whiskers that extend to the non-outlying values. Boxplots are particularly effective for comparing groups
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Center
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The middle of the distribution, usually summarized numerically by the mean or the median
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Distribution
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The distribution of a variable gives:
--Possible values of the variable --Frequency or relative frequency of each value |
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Five-number summary
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A five-number summary for a variable consists of:
--The minimum and maximum --The quartiles Q1 and Q3 --The median |
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Histogram (relative frequency histogram)
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The histogram uses adjacent bars to show the distribution of values in a quantitative variable. Each bar represents the frequency (relative frequency) of values falling in an interval of values
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Interquartile range (IQR)
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The difference between the first and third quartiles. IQR = Q3-Q1
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Mean
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A measure of center found as the sum of the variables divide by the total number of the variables
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Median
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The middle value with half of the data above it and half below it
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Mode
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A peak or local high point in the shape of the distribution of a variable. The apparent location of modes can change as the scale of a histogram is changed
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Multimodal
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Distributions with more than two modes
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Outliers
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Extreme values that don't appear to belong with the rest of the data. They may be unusual values that deserve further investigation or just mistakes; there's no obvious way to tell
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Quartile
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The lower quartile (Q1) is the value with a quarter of the data below it. The upper quartile (Q3) has a quarter of the data above it. The median and quartiles divide the data into four equal parts.
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Range
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The difference between the lowest and the highest values in a data set. Range = maximum-minimum
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Shape
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The visual appearance of the distribution. To describe the shape, look for:
--single versus multiple modes --symmetry versus skewness |
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Skewed
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A distribution is skewed if one tail stretches out farther than the other
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Spread
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The description of how tightly clustered the distribution is around its center. Measures of spread include the IQR and the standard deviation
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Standard deviation
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A measure of spread.
The equation says that SD is found by subtracting the mean from each point on the graph, squaring those values and then adding them all up. Then divide by the amount of points on the graph minus one. |
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Standardized value
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Standardize a value by subtracting the mean and dividing by the standard deviation for the variable. These values, called z-scored, have no units
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Stationary
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A time series is said to be stationary if its statistical properties don't change over time
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Stem-and-leaf display
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A stem and leaf display shows quantitative data values in a way that sketches the distribution of the data. It's best described in detail by example
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Symmetric
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A distribution is symmetric if the two halves on either side of the center look approximately like mirror images of each other
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Tail
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The parts of a distribution that typically trail off on either side
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Time series plot
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Displays data that change over time. Often, successive values are connected with lines to show trends more clearly
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Uniform
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A distribution that's roughly flat
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Unimodal
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Having one mode. This is a useful term for describing the shape of a histogram when it's generally mound-shaped
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Variance
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The standard deviation squared
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Z-score
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A standardized value that tells how many standard deviations a value is from the mean; z-scores have a mean of 0 and a standard deviation of 1
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