Research Methods ❮ 67Test Method
Tests are procedures used to measure attributes of individuals at a particular time and place.
Like surveys, tests can be used to gather huge amounts of information relatively quickly
and cheaply. Results of tests can be used for correlational analysis or for generating ideas
for other research.
For surveys or tests to be accurate measures of behaviors or mental processes, they
must be both reliable and valid. Reliability is consistency or repeatability. Subjects should
answer questions the same way on two different occasions. A subject should also get the
same score on a test on two different occasions. Validity is the extent to which an instru-
ment measures or predicts what it is supposed to. Questions about frequency of showering
would not be valid indicators of cooking ability. Algebra questions would not be valid
measures of what you learned in this chapter.Case study
Another research method, the case study method, is an in-depth examination of a specific
group or single person that typically includes interviews, observations, and test scores. The
intensive description and analysis of the small group or individual is especially useful for
understanding complex or rare phenomena. For example, case studies done on patients
with gunshot wounds to the head enabled scientists to better understand how the loss of
brain tissue affected specific aspects of behavior. Case studies have enabled us to better
understand a wide range of topics, from how the brain processes information to autism.
Clinical psychologists frequently do case studies.elementary statistics
A large amount of data can be collected in research studies. Psychologists need to make sense
of the data. Qualitative data are frequently changed to numerical data for ease of handling.
Quantitative data already are numerical. Numbers that are used simply to name something
are said to be on a nominal scale and can be used to count the number of cases. For
example, for a survey, girls can be designated as “1,” whereas boys can be designated as “2.”
These numbers have no intrinsic meaning. Numbers that can be ranked are said to be on an
ordinal scale, and can be put in order. For example, the highest scorer can be designated as
“1,” the second highest as “2,” the third highest as “3,” etc. These numbers cannot be averaged.
Number 1 could have scored 50 points higher than 2. Number 2 may have scored 4 points
higher than 3. If there is a meaningful difference between each of the numbers, the numbers
are said to be on an interval scale. For example, the difference between 32° Fahrenheit (F)
and 42°F is 10°F. The difference between 64°F and 74°F is also 10°F. However, 64°F is
not twice as hot as 32°F. When a meaningful ratio can be made with two numbers, the
numbers are said to be on a ratio scale. The key difference between an interval scale and a
ratio scale is that the ratio scale has a real or absolute zero point. For quantities of weight,
volume, and distance, zero is a meaningful concept, whereas the meaning of 0°F is arbitrary.
Statistics is a field that involves the analysis of numerical data about representative
samples of populations.Descriptive Statistics
Numbers that summarize a set of research data obtained from a sample are called descrip-
tive statistics. In general, descriptive statistics describe sets of interval or ratio data.
After collecting data, psychologists organize the data to create a frequency distribution, an