Statistics and Probability Dictionary
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Statistics Dictionary
Absolute Value
Accuracy
Addition Rule
Alpha
Alternative Hypothesis
Back-to-Back Stemplots
Bar Chart
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Region of Acceptance
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Scalar Matrix
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Scatterplot
Selection Bias
Set
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Simple Random Sampling
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Skewness
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Standard Deviation
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Statistical Experiment
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Statistics
Stemplot
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Subtraction Rule
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Transpose
Treatment
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Type I Error
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Unbiased Estimate
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Uniform Distribution
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Univariate Data
Variable
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Vector Inner Product
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Vectors
Voluntary Response Bias
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Y Intercept
z Score

Addition Rule
The rule of addition applies to the following situation. We have two events from
the same sample space, and we want to know the probability that either event
occurs.

Rule of Addition If events A and B come
from the same sample space, the probability that event A and/or event B occur
is equal to the probability that event A occurs plus the probability that event
B occurs minus the probability that both events A and B occur.

P(A ∪ B) = P(A) + P(B) - P(A ∩ B)

Note: Invoking the fact that P( A ∩ B ) = P( A )P( B | A ), the Addition Rule can also be expressed as

P(A ∪
B)
= P(A) + P(B) - P(A)P( B | A )