Statistics

Data

Facts and statistics collected together for reference or analysis

Population

The total set of all the observations that are the subject of a study.

Census

an official count or survey of a population, typically recording various details of individuals

sample

A subset from the population

Quantitative or Numerical Variable

A number (quantity), something that can be counted or measured from the individual.

Qualitative or Categorical Variable

A word or name that describes a quality of the individual

Nominal data

Categorical data that has no order or rank. For example, the color of your car, ethnicity, race, or gender.

Ordinal data

Categorical data that has a natural order to it

Interval data

Numeric data where there is a known difference between values, but zero does not mean "nothing."

Ratio Data

Numeric data that has a true zero, meaning when the variable is zero nothing is there. Most measurement data are ratio data.

discrete data

Data with space between possible data values. Graphs are represented by dots.

continuous data

Data that can take on any value. There is no space between data values for a given domain. Graphs are represented by solid lines.

Observational Study

An observational study is when the investigator collects data by observing, measuring, counting, watching or asking questions. The investigator does not change anything.

Experiment

An activity or process that has specific results that can be repeated indefinitely which has a set of well-defined outcomes.

raw data

The original data as it was collected.

Frequency

the number of complete wavelengths that pass a point in a given time

Ogive

a graph that represents the cumulative frequencies for the classes in a frequency distribution

Scatterplot

A scatterplot shows the relationship between two quantitative variables measured on the same individuals.

Stemplot

Also called a stem-and-leaf plot. Data are separated into a stem and leaf by place value and organized in the form of a histogram.

Bar graph

A graph that uses horizontal or vertical bars to display data

Pareto Chart

A bar graph that is ordered from the most frequent down to the least frequent category.

Pie chart

a circular chart divided into triangular areas proportional to the percentages of the whole

mean

arithmetic average of the numbers. This is the center that most people call the average.

Median

data value in the middle of the data that has 50% of the data below that point and 50% of the data above that point.

Mode

data value that occurs the most frequently in the data.

sample size

the number of times a measurement is replicated in data collection

skew

to place at an angle; to cause bias in or distort; asymmetric; distorted or biased

Range

The difference between the largest and smallest data values.

Variance

The average squared distance from the data points to the mean.

Standard Deviation

The average distance of the data points from the mean

Coefficient of Variation

The standard deviation divided by the mean, which allows you to compare variability among data sets when the units or scale is different

biased estimator

If the mean of its sampling distribution is not equal to the true value of the parameter being estimated

unbiased estimator

The mean of its sampling distribution is equal to the true value of the parameter being estimated

Z-Score

The number of standard deviations a data point is from the mean.

percentiles

indicate the distance of a score from 0

Quartile

Numbers that divide a data set into fourths. One fourth (or a quarter) of the data falls between consecutive quartiles.

Interquartile Range (IQR)

The distance between the first and third quartile.

box plot

A graph that displays the highest and lowest quarters of data as whiskers, the middle two quarters of the data as a box, and the median

potential outlier

anything more than 2 standard deviations away from the mean