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41 Cards in this Set
- Front
- Back
individuals
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are the objects described by a set of data.
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variable
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any characteristic of an individuals.
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categorical variable
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places an individual into one of several groups or categories. (distribution is measured in count or percent)
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quantitative variable
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takes numerical values for which arithmetic operations such as adding and averaging make sense.
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distribution
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tells us what values the variable takes and how often it takes these values.
use words like center,spread and shape. |
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outlier
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an individual observation that falls outside the overall pattern of the graph.
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symmetric
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the left and right sides are mirror images.
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skewed to the right
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if the right sides extends farther out then the left side. (tail off to the right)
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skewed left
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if the left side of the histogram extends much farther out than the right side. (tail off to the left)
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P-th percentile
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the value such that p percent of the observations fall at or below it.
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relative frequency
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count per class/total x 100%
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cumulative frequency
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add the counts of the current class and all classes below that level (add classes together as each class increases)
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relative cumulative frequency
(ojive graph) |
cumulative frequency per class/total x100%
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IQR
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Q3-Q1= ?
where Q3 is the median of all observations to the RIGHT of the overall median and Q1= median of all observations to the LEFT of the overall median. |
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upper outlier cut off
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Q3 + (1.5 X IQR)
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lower outlier cut off
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Q1 - ( 1.5 x IQR )
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5 number summary
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minimum , Q1, Median, Q3, Maximum
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standard deviation
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the distance of #s from the mean
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density curve
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is always on or above the horizontal axis and has an area of exactly 1 underneath it. THE MEDIAN SPLITS THE CURVE IN HALF.
THE MEAN IS THE POINT AT WHICH THE CURVE WOULD BALANCE. |
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response variable
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measures an outcome of a study
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exploratory variable
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attempts to explain the observed outcomes. (independent variable)
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scatterplot
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shows the relationship between two quantitative variables measured on the same individuals.
notice the: overall pattern, strength, form, and outliers |
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regression line
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a straight line that describes how response variable y changes as an explanatory variable x changes.
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coefficent of determination
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r2-ed
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residuals
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the difference between an observed value and predicted value.
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linear growth
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increases by a fixed amount
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exponential growth
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increases by a fixed percentage
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extrapolation
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the use of a regression line for prediction far outside the domain of values of the x and y
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lurking variable
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not among the x and y variables but may influence the interpretations of the relationship between x and y
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are usually too high when applied to individuals
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correlations based on averaged data.
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simpsons paradox
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the reversal of the direction of a comparison or an association when data from several groups are combined to form a single group.
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observational study
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observes individuals and measures variables of interest but does not influence responses.
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experiment
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deliberately imposes some treatment on individuals in order to observe their responses.
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population
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the entire group of individuals we want information about.
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sample
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part of the population that is actually examined.
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census
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attempts to contact every individual in the entire population.
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voluntary response sample
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consists of people who choose themselvers by responding to a general appeal. BIASED - brings out especially those with negative opinions
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convenience sampling
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chooses individuals easiest to reach - BIASED
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biased
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systematically favors certain outcomes.
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SRS or simple random sample
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eveyrone in the population has an eaqual chance of being chosen.
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strata
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groups of similar individuals
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