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40 Cards in this Set
- Front
- Back
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individuals
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the objects described by a set of data
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variables
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any characteristic of an individual
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categorical variable
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places an individual into one of several groups
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quantitative variable
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takes a numerical value that can be used for calculations
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distribution
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what values a variable can take and how often it takes them
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center
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a value that divides the observations in half
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spread
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the smallest and largest values
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outlier
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an individual observation that falls outside the overall pattern of the graph; to be a true outlier, it must fall more than 1.5 times the IQR above the 3rd quartile or below the first quartile
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bimodal shape
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graph shows two peaks
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unimodal shape
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graph shows one peak
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symmetric
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the right and left sides of the histogram are approximately mirror images of each other
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skewed
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a distribution is skewed to the right (or left) if the right (or left) side of the histogram extends much farther out than the left side
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Pth percentile
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the value such that p percent of the observations fall at or below it
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trend
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a long term upward or downward movement over time
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seasonal variation
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a pattern that repeats itself at regular intervals
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mean
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average; the most common measure of the center of distribution; x bar
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Σ - sigma
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add all the values
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median
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midpoint of the distribution
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resistant
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not dramatically affected by adding an extreme value
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range
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the difference between the largest and smallest observations
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quartiles
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mark the middle half of the observations
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First Quartile (Q1)
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one-fourth of the observations are below this value
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Third Quartile (Q3)
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one-fourth of the observations are above this value
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Interquartile Range
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the distance between the first and third quartiles
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Five Number Summary
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smallest, Q1, median, Q3, largest - these describe the center and spread of a distribution
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variance
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the average of the squares of the deviations from the mean
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standard deviation
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measures spread by looking at how far the observations are from the mean
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degrees of freedom
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(n-1) describes amount of choice
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linear transformation
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changing the units of measurement
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mathematical model
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an idealized description of an overall pattern, ignoring minor irregularities and outliers
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density curve
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a curve with an area of 1 for which the area under the curve for a range of values represents the proportion of all observations that fall in that range
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frequency histogram
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plots the frequency of each outcome in a histogram
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uniform distribution
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all bars have the same height
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normal distributions
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symmetric, single peaked, bell shaped
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inflection points
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the points at which the curve changes from falling more steeply to falling less steeply. They are located at a distance equal to the standard deviation on either side of the mean
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standardizing
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changing to units of size σ about μ as a center
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Z-score
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standardized value that tells hows many standard deviations the original observation falls away from the mean and in which direction z= (x-μ)/σ
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standard normal distribution
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N(0,1)- a normal distribution with a mean of 0 and a standard deviation of 1
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Z table
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the value in the table shows the proportion of observations to the left of the z score
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normal probability plot
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used to assess normality. if the data is approximately normal, the normal probability plot will be roughly linear.
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