Test Method
Testsare 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. Reliabilityis 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. Validityis the extent to which an instrument meas-
ures 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 scaleand can be used to count the number of cases. For exam-
ple, 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 42F is 10F. The difference between 64F and 74F is also 10F. H o w e v e r , 6 4F is not
twice as hot as 32F. 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 0F is arbitrary.
Statisticsis 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
orderly arrangement of scores indicating the frequency of each score or group of scores. TheResearch Methods 55