Biostatistics

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categorical variable

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variable expressed as categories; can be ordinal or discrete

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nominal

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categorical variable with values that cannot be ranked

ex. sex (male/female), blood type (A, B, AB, O)

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ordinal

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categorical variable with values that can be ranked

ex. cloudiness (overcast, mostly cloudy, partly cloudy, sunny)

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quantitative variable

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

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frequency

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number of occurrences

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descriptive statistics

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statistics that describe the data

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sample

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

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population

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party on which inferences are being made

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observational unit (case)

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instance of the sample; specimen

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statistic

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numerical measure calculated from data

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measures of center

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

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measures of dispersion

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include range, standard deviation, coefficient of variation

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robust (resistant)

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value of statistic relatively unaffected by changes in a small portion

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range

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difference between largest and smallest observations in a sample

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coefficient of variation

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the standard deviation expressed as a percentage of the mean

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statistical inference

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

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frequency distribution

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display of frequency of each value in a data set

shape, center and spread of distribution is significant when discussing a set of data

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density curve

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smooth-curve representation of frequency distribution

area under density curve between A and B = proportion of Y values between A and B

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p

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population proportion

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p̂ (p-hat)

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sample proportion; and estimate of p (population proportion)

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μ

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population mean

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σ

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population standard deviation

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degrees of freedom

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n - 1

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ȳ (y-bar)

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sample mean

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first quartile (Q₁)

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median of data values in lower half or data set

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third quartile (Q₃)

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median of data values in upper half of data set

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interquartile range (IQR)

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difference between first and third quartiles

IQR = Q₃ - Q₁

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five-number summary

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minimum, maximum, median, quartiles

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sampling distribution

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

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sampling distribution of p̂

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collection of probabilities of all various possible values of p̂

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standard error

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describes uncertainty in the mean of the data

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standard deviation

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describes dispersion of the data

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Student's t distributions

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

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normal distributions

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distributions represented by normal curve: standardized symmetric bell-shaped curve

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binomial distributions

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

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binomial random variable conditions (BInS)

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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