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36 Cards in this Set
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categorical variable

variable expressed as categories; can be ordinal or discrete

nominal

categorical variable with values that cannot be ranked
ex. sex (male/female), blood type (A, B, AB, O) 
ordinal

categorical variable with values that can be ranked
ex. cloudiness (overcast, mostly cloudy, partly cloudy, sunny) 
quantitative variable

variable that can be expressed in amounts numbers; can be discrete or continuous

frequency

number of occurrences

descriptive statistics

statistics that describe the data

sample

collection of person or things on which one or more variables is measured

population

party on which inferences are being made

observational unit (case)

instance of the sample; specimen

statistic

numerical measure calculated from data

measures of center

measures meant to define the "center" or "typical value" of observations in a sample; include mean, median

measures of dispersion

include range, standard deviation, coefficient of variation

robust (resistant)

value of statistic relatively unaffected by changes in a small portion

range

difference between largest and smallest observations in a sample

coefficient of variation

the standard deviation expressed as a percentage of the mean

statistical inference

process of drawing conclusion about a population based on observations in a sample of that population

frequency distribution

display of frequency of each value in a data set
shape, center and spread of distribution is significant when discussing a set of data 
density curve

smoothcurve representation of frequency distribution
area under density curve between A and B = proportion of Y values between A and B 
p

population proportion

p̂ (phat)

sample proportion; and estimate of p (population proportion)

μ

population mean

σ

population standard deviation

degrees of freedom

n  1

ȳ (ybar)

sample mean

first quartile (Q₁)

median of data values in lower half or data set

third quartile (Q₃)

median of data values in upper half of data set

interquartile range (IQR)

difference between first and third quartiles
IQR = Q₃  Q₁ 
fivenumber summary

minimum, maximum, median, quartiles

sampling distribution

describes how close resemblance between sample and population is likely to be

sampling distribution of p̂

collection of probabilities of all various possible values of p̂

standard error

describes uncertainty in the mean of the data

standard deviation

describes dispersion of the data

Student's t distributions

theoretical continuous distributions used for construction of confidence intervals; shape depends on degrees of freedom (df)

normal distributions

distributions represented by normal curve: standardized symmetric bellshaped curve

binomial distributions

for binomial random variable Y: probability that n trials result in j successes

binomial random variable conditions (BInS)

Binary outcomes: two possible outcomes for each trial
Independent trials: outcomes of trials are independent of each other n is fixed Same value of p: probability of success on a single trial is same for all trials 