Psychological tests (II)
The norm group should be chosen as to allow reasonable comparisons. If the
test is intended to be given to third-grade pupils, the norm group must be
composed of pupils of the same grade. The score may take the form of a grade-
equivalent score, or of a percentile score. In the first case, a score of 5
would mean that the subject scored as well as the middle of the norm group.
In the second case, a score of 95 would mean that the subject scored better
than 94 percent of the norm group.
The use of objective tests--such as standardized multiple-choice tests--was
advocated on the grounds of avoiding discrimination when attempting to
measure aptitudes and achievements of people with diverse cultural
background. Nevertheless, such criticisms have been raised against tests
using this methodology such as intelligence tests. The argument is that they
discriminate against Blacks, Hispanics, women, and other groups who differ
from the norm. To fully comprehend the controversy, a certain knowledge of
statistics and its key concepts (average, deviation, and the like) is needed.
Statistics
Statistics is a scientific discipline which deals with data gathered through
observation and attempts to determine population characteristics by analyzing
data from samples. Collection and interpretation of data are the main
problems faced by statistics. Although examples of data collection can be
found in the Old Testament, statistics as a modern science is considered to
be born in the 19th century.
Statistics is used in many fields of science as a means to shed more light on
complex problems. To reach this goal, some conditions must be observed.
Sample data must be ensured to be representative of the population by using a
random sampling method. In biomedical research, experimental treatments must
be controlled with a group of patients who receive no treatment. Without
precautions of this kind the results of observation or experimenting should
not be taken as scientific evidence.
Average and standard deviation
Observation results are concisely expressed using a small set of numbers
which collectively receive the name of statistics. A statistic is, for
example, the average of a set (also called the mean). The average is the most
probable value in a random sample. A graph is usually drawn called a
histogram, where the observed quantity of each value of the measured variable
(in the X-axis) is plotted on the Y-axis. The average usually corresponds to
the higher bar in the graph, marking the location of the population.
Another useful statistic is the standard deviation, which is a measure of the
distribution's spread or dispersion. The average and the standard deviation
are usually enunciated together because the average alone can be a misleading
figure. When the individual measurements are very different, it is said that
the data set is scattered or that the data distribution is highly dispersed.
In this case, although the average is always the most probable value (as
stated by the Central Limit theorem), its probability is low. Therefore, the
average is not a good predictor of the variable's value for an individual
chosen at random
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