Personality Chapter 2: The Scientific Study of People
The three major methods in personality research: case studies; correlational studies (using
questionnaires); and laboratory experiments.
1) Questions to be Addressed in this Chapter
The personality scientist must formulate his or her idea very explicitly, so that they can be tested
by objective scientific evidence. Scientists follow established procedures to ensure that they obtain
information that is as objective and accurate as possible. They check these procedures to ensure
that their observations are stable and reliable. They report the procedures in publications so that
other investigators can replicate their procedures and verify their findings.
Research involves the systematic study of relationships among events. Generally, we need a theory
to identify the events that are most important to study. We also need a theory to tell us how to
study them. Theory without research can be mere speculation; research without theory is an
2) The Data of Personality Psychology
A) Lots of Data
There are 4 categories of data that one might use in research: 1) life record data (L-Data), 2)
observer data (O-Data), 3) test data (T-Data), and 4) self-report data (S-Data)or LOTS of
1) L-Data consist of information that can be obtained from a persons life history or life record.
(ex: official school records, criminal records, ...) However, such objective records are not
2) O-Data consist of information provided by knowledgeable observers such as parents, friends,
or teachers. Generally, such persons are provided with a questionnaire with which they rate
the target individuals personality characteristics. Sometimes observers are trained to
observe individuals in their daily lives and to make personality ratings based on these
observations. O-data can consist of observations of very specific pieces of behaviour or of
more general ratings based in observations of behaviour. In addition, data on any individual
can be obtained from one observer or from multiple observers.
3) T-Data consist of information obtained from experimental procedures or standardized tests.
4) S-Data consist of information provided by the subject himself or herself. Typically such data
are in the form of responses to questionnaires. Personality questionnaires can be relevant to
single personality characteristics (ex: optimism) or can attempt to cover the entire domain of
Self-reports clearly have limitations. People may be unaware of some of their own
psychological characteristics. They may be motivated to present themselves in a positive
manner to the psychologist administering the test. However, self-report measures are
convenient, in that they are relatively easy to obtain. Thus, self-reports are the most
commonly used source of data in personality psychology.
Researchers do not need to choose only one source of data for their research. Quite commonly,
they combine data sources.
Some forms of data do not easily fit into this 4-category LOTS scheme. Thus, additional
categories may be necessary to capture the diversity of data that the contemporary psychologist
uses to assess personality characteristics. For example: Implicit Individual-Difference Measures:
these measures are designed to tap beliefs or self-evaluations of which people may not be
consciously aware; one popular implicit measure involves reaction time: how long it takes for
people to answer a question. Other researchers employ diary methods: techniques in which
people are asked to report about their psychological experiences soon after their occurrence,
rather than completing a questionnaire that inquires about things that have happened in thedistant past. Diary methods have a major advantage: diary methods avoid the problem of
forgetting, as well as eliminate biases that may occur when people try to remember emotionally
significant events that occurred far in the past.
B) How do Data from Different Sources Relate to One Another?
Self-reports (S-data) are often discrepant from scores obtained from laboratory procedures (T-
data). Self-report questionnaires tend to involve broad judgements that relate to a wide variety
of situations whereas experimental procedures measure personality characteristics in a very
Self-report (S-data) and observer reports (O-data) tend to be related more closely. When the
personality characteristics being rated is highly evaluative, self-perception biases enter the
rating process, lowering agreement between self and observer ratings. Moreover, some
personality characteristics are more observable and easier to judge than others, leading to
greater agreement between self and observer ratings as well as to greater agreement among
ratings obtained from different observers of the same person. Furthermore, some individuals
appear to be easier to read or more judgable than others.
Self-report questionnaires have a clear advantage: people know a lot about themselves. Yet,
self-report methods have limits: peoples descriptions of themselves on questionnaires can be
influenced by irrelevant factors such as the phrasing of the question and the order in which
items appear on a test; people may also lie or may unconsciously distort their questionnaire
Problems may also arise in questionnaire ratings by others who know the person: different raters
may sometimes rate the same person in quite different ways.
Objective measures of behaviour and of biological systems underlying that behaviour may be a
more reliable source of evidence for building a science of personality. Yet the personality
psychologist is often inter