1.8 Indicate whether each of the following studies is an experiment or an observational study. If
it is an experiment, identify the independent variable and note any possible confounding
variables.
(a) A psychologist
...
1.8 Indicate whether each of the following studies is an experiment or an observational study. If
it is an experiment, identify the independent variable and note any possible confounding
variables.
(a) A psychologist uses chimpanzees to test the notion that more crowded living conditions
trigger aggressive behavior. Chimps are placed, according to an impartial assignment rule, in
cages with either one, several, or many other chimps. Subsequently, during a standard
observation period, each chimp is assigned a score based on its aggressive behavior toward a
chimp-like stuffed doll.
This is an experiment. The independent variable is the number of chimps that are placed together.
The example states they are placed according to an impartial assignment rule. A potential
confound variable in this study could include cage size, age, or gender or the chimps.
(b) An investigator wishes to test whether, when compared with recognized scientists, recognized
artists tend to be born under different astrological signs.
This is an observational study because the astrological sign according to birthdate cannot be
manipulated, it is just observed.
(c) To determine whether there is a relationship between the sexual codes of primitive tribes and
their behavior toward neighboring tribes, an anthropologist consults avail-able records,
classifying each tribe on the basis of its sexual codes (permissive or repressive) and its behavior
toward neighboring tribes (friendly or hostile).
This is an observational study because the researcher cannot change the sexual codes of primitive
tribes. They are just observing the records and recording the data.
(d) In a study of group problem solving, an investigator assigns college students to groups of
two, three, or four students and measures the amount of time required by each group to solve a
complex puzzle.
This is an experiment. The independent variable would be the size of the group that the
researcher assigns the students into. A potential confound could be because of no random
assignment. If random assignment was done to place students into groups, it would not be a
confound.
(e) A school psychologist wishes to determine whether reading comprehension scores are related
to the number of months of formal education, as reported on school transcripts, for a group of
12-year-old migrant children.
This is an observational study since the tests have already been previously completed and have
been recorded on the transcript. If the researcher was manipulating the exams, it would change
the study. However, the researcher is strictly just recording the data that has already been
completed.
(f) To determine whether Graduate Record Exam (GRE) scores can be increased by cramming,
an investigator allows college students to choose to participate in either a GRE test-taking
workshop or a control (non-test-taking) workshop and then com-pares the GRE scores earned
subsequently by the two groups of students.
This is an experiment. The independent variable is the type of workshop that they students are
participating in. A potential confound in this study could be studying. If some students already
studied previously or had more knowledge of the GRE than others, they may do better regardless
of the workshop. This would make is a confound.
(g) A social scientist wishes to determine whether there is a relationship between the
attractiveness scores (on a 100-point scale) assigned to college students by a panel of peers and
their scores on a paper-and-pencil test of anxiety.
This is an observational study. The researcher is the observing the results of the attractiveness
scores and the paper-and-pencil test of anxiety. The researcher is not manipulating the
environment in any way and is just overserving the results.
(h) A political scientist wishes to determine whether males and females differ with respect to
their attitudes toward defense spending by the federal government. She asks each person if he or
she thinks that the current level of defense spending should be increased, remain the same, or be
decreased.
This is an experiment. The independent variable is gender. Potential confounds could include
political affiliation or age of the person. Another confound could be education and knowledge of
defense spending. Some individuals may know more about defense spending than others.
(i) Investigators found that four year-old children who delayed eating one marshmallow in order
to eat two marshmallows later, scored higher than non-delayers on the Scholastic Aptitude Test
(SAT) taken over a decade later.
This is an observational study. The researchers recorded the results and did not manipulate any
variables.
1.9 Recent studies, as summarized, for example, in E. Mortensen et al. (2002). The association
between duration of breastfeeding and adult intelligence. Journal of the American Medical
Association, 287, 2365–2371, suggest that breastfeeding of infants may increase their subsequent
cognitive (IQ) development. Both experiments and observational studies are cited.
(a) What determines whether some of these studies are experiments?
An experiment is when something is applied to a certain group or individual to measure an
outcome or effect. This could include givin
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