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26 Cards in this Set

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What is a parameter?
The summary measure calculated for population data.
What is a statistic?
The summary measure calculated for sample data.
What is a population?
All elements whose characteristics are being studied.
What is a sample?
A portion of the population that is selected for study.
Part of a bigger picture...
What is a qualitative variable?
-categorical
-does not contain numbers but rather data that can fit into 2 or more non-numerical categories
think qualitative vs. quantitative
What is a quantitative variable?
-numerical, numeric values assigned
-can be discrete or continuous
think quantitative vs. qualitative
What is a discrete variable?
-quantitative variable
-contains a certain value with no intermediate values
ie. integers, grades
What is a continuous variable?
-quantitative variable
-numerical value over a certain interval or intervals
ie. GPA, gas prices
continuous, like continuing over a range
What does a histogram show?
Compared to boxplots, what does it represent?
-number of modes (unimodal or bimodal)
-tail weight
-shape (symmetry and skew)
-->skewness is identified by looking at TAIL
-compared to boxplots, best representation of MODALITY
What does a boxplot show?
Compared to histograms, what does it represent?
-outliers
-shape (symmetry and skew)
-->skewness is identified by looking at GRAPH WITHIN ITSELF or GRAPH AS A WHOLE
-compared to histograms, best representation of SKEWNESS
What is an outlier?
An observation that falls well above or well below (more than three standard deviations) the bulk of the data.
What is the median?
The value of the midpoint of a data set that has been ranked in order (increasing or decreasing)
If dataset has an even number of values, take the average of the two middle values.
What is the mean?
The average of all the values.
What is the mode?
The most frequent value in a dataset.
Graphically, relating MEAN and MEDIAN, how is SYMMETRY shown?
median = mean
Graphically, relating MEAN and MEDIAN, how is LEFT SKEW shown?
median > mean
Graphically, relating MEAN and MEDIAN, how is RIGHT SKEW shown?
median < mean
What is affected by the 'Outlier effect'?
-mean

-median is resistant
What is variance?
The average of squared deviations.
-never negative
-square the original units
-uses (n-1) degrees of freedom to account for the remaining observations.
What is Standard Deviation?
The square root of variance. The larger is is, the larger is the spread of the data.
-never negative
What is a scatterplot?
A graphical display of 2 quantitative variables (x=explanatory, y=responding)
What is correlation? Is it sensitive to outliers? What relationship does it assume?
Summary measure that describes the strength of linear association.
'r' - (-1<r<1)
r>1 = positive linear
r<1 = negative linear
closer to 0, less association.
-sensitive to outliers.
-assume STRAIGHT LINE relationship
What does R-squared represent?
The proportion in variation of y explained by x.
What is a residual? When is it significant?
The prediction error, the difference between the observed and predicted value. The closer it is to zero, the less difference there is, so the better is the prediction.
What is an observational study?
Researcher observes characteristics of subjects in samples from populations of interest.
key word: OBSERVational
What is an experimental study?
Researcher applies different treatments to different subjects and observes the outcomes.
key word: EXPERIMENTal