Chapter 2 Flashcards
cumulative frequency graph curve
descriptive statistics
rectangular curve
SAS
SPSS
h
Range
the distance in numerical value from the highest (H) to the
lowest (L) score. It is calculated by subtracting the lowest score from the highest score:
R = H − L.
Simple Frequency Distribution
used to organize larger data sets; an ordered listing of the variable being studied (X), with a frequency column (f) that indicates the number of cases at each given value of X.
Grouped Frequency Distribution
an ordered listing of, in one column, a
variable (X) in groups of scores and, in a second column [the frequency column (f)], the number of persons who performed in each group of scores.
Interval Size
the size of a group of scores on a given variable; is
i = range/15.
Apparent Limit of each group are…
the integer values listed for each group
in the grouped frequency distribution.
Real Limits of each group are…
the assumed upper and lower score values in each group, created to the degree of accuracy required by the data; the real limits define the true upper and lower limits of the group.
The lower real limit of the 80-to-84 group is…
79.5
The upper real limit of the 80-to-84 group is…
84.49999
Spreadsheet
Tables present data in a row-and-column format. In computer terminology, a table is sometimes
Multivariate
data with more than one variable measured on each subject
Excel
can easily sum-mate columns or rows, calculate descriptive statistics, and perform other types of statistical tests on uni-or multivariate data
Graphs
is a figurative, or visual, repre-sentation of data; helpful for comparing two or more sets of data or for showing trends. All should include at least three characteristics: (a) a title, (b) a label on the X-axis (the abscissa), and (c) a label on the Y-axis (the ordinate).
Histogram
(or bar graph). It is usually constructed from a grouped frequency distribution, but it may also originate from
a simple frequency distribution.
Frequency Polygon
constructed from frequency distribution data; a line graph of the scores plotted against the frequency.
Cumulative Frequency Graph
or cumulative frequency curve; a line graph of ordered scores on the X-axis plotted against the number of subjects who scored at or below a given score on the Y-axis.
Curve
the line that results when scores (X) are plotted against frequency (Y) on a graph. The shape depends on the distribution of the data; presents a visual picture that permits us to see trends in the data that we may not easily observe when looking at a table.
Normal Curve
characterized by symmetrical distribution of data about the center of the curve in a special manner. The mean (average), the median (50th percentile), and the mode (score with the highest frequency) are all located at the middle of the curve. The frequency of scores declines in a predictable manner as the scores deviate farther and farther from the center of the curve.
Central Limit Theorem
, a sum of random numbers becomes normally distributed as more and more of the random numbers are added together
Mesokurtic
When most scores fall in the midrange and the frequency of the scores tapers off symmetrically toward the tails, the familiar bell-shaped curve occurs
Platykurtic Curve
if the results have a very wide range of scores with low frequencies in the midrange, the curve
Leptokurtic Curve
opposite of the platykurtic curve; results when the range of the group is limited and many scores are close to the middle.
Mode
score with the highest frequency; on the normal curve, a single mode is always in the middle
Bimodal
(multimodal) some distributions of data have two or more modes; If one mode is higher than the other, the modes are referred to as the major and minor modes. When such data distributions are plotted, they have two or more humps representing the cluster-ing of scores; not normal curves.
Skewed
sometimes the data result in a curve that is not normal, that is, the tails of the curve are not symmetrical; a disproportionate number of the subjects score toward one end of the scale
Ceiling Effect
when there is a limit on how high scores can be and scores tend to bunch around that limit.
Floor Effect
can occur when there is a limit on how low scores can go and scores tend to bunch around that limit.
U-shaped curve
the result of a high frequency of values at the extremes of the scale and a low frequency in the middle.
J-curve
results when frequency is high at one end of the scale, decreases
rapidly, and then flattens and reduces to almost zero at the other end of the scale; curve is different from a straight line, in which frequency decreases uniformly from one end of the scale to the other; can be positive or negative in direc-tion, depending on the orientation of the lower tail of the curve. If the tail points to the positive end of the X-axis, the curve is positive. (may also be inverted)
