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discrete
type of quantitative variable that can not be divided (whole # only)

Tail to the left
skewed left

If histogram is symmetric... mean and median
are similar

If histogram is asymmetric median is...
more useful than mean


outlier
1.5*IQR +/ Q_{1/3}

Standard Deviation
 how are on average samples are from the mean

Sample Variance
Square of the Sample standard Deviation

Coefficient of Variation
 gives a unitless quantity
 it is sd/ȳ
 hard when close to zero
 need nonnegative

When bell shaped:
+/ 1 SD has ___ %
+/ 2 SD has ___ %
+/ 3 SD has ___ %

linear transformation
 linear = 1 multiplicative factor & 1 additive factor
 For means: use same formula
 For SD: additive factor is cancelled and just want absolute value of multiplicative
 For Variance: square the multiplicative

Frequency Interpretation
 Interpreting probability that you would actually experiment each time
 Not the only way to interpret

Probability of nonoverlapping events
OR events
add P{1} + P{2}

Probablility of independent events
AND events
P{1}*P{2}

For simultaneous events visualize with...
venn diagram

For sequential events visualize with...
 Probability trees
 (medical tests)
 AND events

sensitivity v. specificity
 sensitivity % true positives
 Specificity % True negatives


