Data
Information.
Data Distribution
A listing of the values or responses associated with a particular variable in a data set.
Data Point
The individual pieces of information in a data set.
Data Set
The collection or bundle of information relative to specific variables.
Descriptive Statistics
Statistical procedures used to summarize or describe data.
Frequency Distribution
A table or graph that indicates how many times a value or score appears in a set of values or scores.
Inferential Statistics
Statistical procedures used to make statements or inferences about a population, based on sample statistics.
Interval Level of Measurement
A system of measurement based on an underlying scale of equal intervals. See also interval/ratio level of measurement and ratio level of measurement.
Interval/Ratio Level of Measurement
Since there is no practical difference between the interval and ratio levels of measurement when it comes to statistical analysis, the terms are often combined to refer to any scale of measurement that is either interval or ratio.
Nominal Level of Measurement
The simplest level of measurement; a system of measurement based on categories that are mutually exclusive and collectively exhaustive.
Ordinal Level of Measurement
A level of measurement that presumes the notion of order (greater than and lesser than).
Parameter
A characteristic of a population.
Population
All possible cases; sometimes referred to as the universe. It is often thought of as the total collection of cases that you're interested in.
Ratio Level of Measurement
A level of measurement that has all the properties of the interval level of measurement, plus the presence (or possibility) of a true or legitimate zero (0) point. See interval/ratio level of measurement.
Sample
A portion of a population.
Statistic
A characteristic of a sample. Compare parameter.
Universe
See population.
Variable
Anything that can take on different quantities or qualities; anything that can vary.
average deviation
See mean deviation.
bimodal distribution
A distribution with two modes.
central tendency
The center or typicality of a distribution. The three most common measures of central tendency are the mean, median, and mode.
dispersion (variability)
The extent to which the scores in a distribution are spread around the mean value or throughout the distribution. The two most commonly used measures of dispersion are the variance and the standard deviation.
mean
The most widely used measure of central tendency. The mean is calculated by summing all the scores in a distribution and dividing the sum by the total number of cases in the distribution.
mean deviation
An infrequently used measure of dispersion based, in part, on the absolute deviations from the mean of the distribution. Also known as the average deviation.
median
The score that divides a distribution in half; the midpoint of a distribution, or the point above and below which one-half of the scores or values are located. The formula for the median is a positional formula; it will tell you the position of the median
mode
The response or value that appears most frequently in a distribution. The mode is the only measure of central tendency that is appropriate for nominal level data.
mu (?)
The mean of a population.
range
A statement of the difference between the highest and lowest scores or values in a distribution. As a measure of dispersion or variability, the range is simple to calculate, but it doesn't say much about the distribution.
standard deviation
A widely used measure of dispersion or variability. The standard deviation is the square root of the variance.
unimodal distribution
A distribution with only one mode.
variance
A widely used measure of dispersion or variability. The variance is equal to the standard deviation squared.
1-2-3 Rule
A statement of how much area under the normal curve is found between �1, �2, and �3 standard deviations from the mean.
frequency distribution
A table or graph that indicates how many times a value or score appears in a set of values or scores.
negative skew
The shape of a distribution that includes some extremely low scores or values. A distribution is said to have a negative skew if the tail of the distribution points toward the left.
normal curve
A unimodal, symmetrial curve that is mathematically defined on the basis of the mean and standard deviation of an underlying distribution.
point of inflection
The point at which a normal curve begins to change direction. It is one standard deviation above or below the mean of the underlying distribution.
positive skew
The shape of a distribution that includes some extremely high scores or values. A distribution is said to have a positive skew if the tail of the distribution points toward the right.
skewed distribution
A distribution that departs from symmetry, in the sense that most of the cases are concentrated at one end of the distribution.
symmetrical distribution
A distribution in which the two halves are mirror images of each other.
tail of the distribution
In a skewed distribution, the elongated portion of the curve.