Chapter 2: Frequency Distributions

apparent limits

The score values that appear as the lowest score and the highest score in an interval.

skewed distribution

The scores tend to pile up toward one end of the scale and taper off gradually at the other end.

tail of a distribution

The section where the scores taper off toward one end of a distribution.

cumulative frequency (cf)

The total of a frequency and all frequencies so far in a frequency distribution.

negatively skewed distribution

A distribution with the tail on the left-hand side. A distribution where the scores pile up on the right side and taper off to the left.

positively skewed distribution

A distribution with the tail on the right-hand side, because the tail points toward the positive (above-zero) end of the X-axis. A distribution where the scores pile up on the left side and taper off to the right.

polygon

A graph consisting of a line that connects a series of dots. A dot is placed above each score or interval so that the height of the dot corresponds to the frequency.

histogram

A graph showing a bar above each score or interval so that the height of the bar corresponds to the frequency and width extends to the real limits.

class interval

A group of scores in a grouped frequency distribution.

stem and leaf display

A plot where each data value is split into a "leaf" (usually the last digit) and a "stem" (the other digits).

interpolation

An estimation of a value within two known values in a sequence of values.

frequency distribution

An organized tabulation of the number of individuals located in each category on the scale of measurement.

symmetrical distribution

It is possible to draw a vertical line through the middle so that one side of the distribution is a mirror image of the other.

range

The difference between the lowest and highest values.

grouped frequency distribution

The organizing of raw data in table form, using classes and frequencies. A frequency distribution where scores are grouped into intervals rather than listed as individual values.

percentile rank

The percentage of individuals in the distribution with scores equal to or less than the particular value.

relative frequency

The proportion of the total distribution rather than the absolute frequency. Used for population distributions for which the absolute number of individuals is not known for each category.

percentile

When a score is identified by its percentile rank.

cumulative percentage (c%)

[]Cumulative percentage is another way of expressing frequency distribution. It calculates the percentage of the cumulative frequency within each interval, much as relative frequency distribution calculates the percentage of frequency. [] The main advantage of cumulative percentage over cumulative frequency as a measure of frequency distribution is that it provides an easier way to compare different sets of data.