This document discusses various types of quasi-experimental research designs used to study genetic and health-related topics when random assignment is not possible. It describes retrospective and prospective studies, case studies, twin studies, and adoption studies as ways to examine relationships between variables. Key factors like heredity, environment, age, and epigenetics are discussed in relation to traits, diseases, and health outcomes. Combining experimental and non-experimental methods is recommended to strengthen research conclusions.

1. Quasi Experimental Research and
Genetic studies

2.  They look like experiments but they are not
because they have separate group of subjects
, but they are not because the subjects were
not randomly assigned to groups.
 In some quasi experiments independent
variables are manipulated but in some they
are not.
 A commonly used quasi-experimental
approach is called an expost facto study in
which subjects are categorized and placed in
groups on the basis of the existing variable.

3.  For example groups based on gender (male
and female), cholesterol level (high, moderate
and low).
 A Quasi experimental study relating to the
cholesterol theory of heart disease can be
done in the following way.
 Suppose a researcher wants to see that if
people’s cholesterol level at the time of the
heart attack is related to their severity of
heart attack.

4.  For this study the records of heart disease
patients are consulted.
 Then the patients were characterized into two
groups :
 Those having high cholesterol level when they were
admitted in the hospital
 Those having low cholesterol level when they were
admitted in the hospital.
It was found that patients having high cholesterol
level had more severe heart attacks.

5.  But we cannot conclude that it is the higher
blood cholesterol level only which causes
heart attack
 In general , the conclusions from quasi
experimental studies are basically co
relational and the relationships they reveal do
not become casual simply because we
categorize subjects.

6.  Retrospective approach has been derived
from the prefix ‘retro’ meaning backward and
spective comes from the latin word to ‘look’.
 It uses the procedure that look back at the
histories of subjects who have or do not have
this disease. The purpose is to find
commonalities in the people’s history that
may suggest why they have developed this
disease.

7.  The retrospective approach can be used in quasi-
experimental studies also.
 For the example cited above the individuals are
divided into two groups. One group would
consist of people who have already developed a
disease and the other group would consist of
people without the disease.
 Then the two groups would be examined for
characteristics of their histories that are common
to one group but not to the other.
 For example one group reported having eaten
high cholesterol diet as compared to the other
group.

8.  Retrospective report has a potential
shortcoming because in this we have to rely
on the person’s memories so the likelihood of
inaccuracy increases.

9.  It uses procedures that look forward in the
lives of the individuals , by studying whether
the differences in a variable at one point of
time are related to differences in another
variable at a later time.
 By using prospective approach we would start
by recruiting people say 2000 who did not
have illness like heart disease and then
studying them again after several years at
regular intervals.

10.  Doctors examine the individuals , check their
medical records and ask them about their
diet and cholesterol intake and then
categorize the people into two groups as
having or not having a heart attack.
 Retrospective and Prospective Approaches
have been developed by epidemiologists and
they have been helpful in identifying risk
factors for specific illnesses

11.  An essential research approach in studying
life span development is to examine and
compare subjects at different ages.
 We can assign individuals to groups based on
their age.
 This approach is quasi experimental and
therefore age cannot be viewed as a cause of
health or behavior.

12.  Two basic approaches are used for studying
the age variable.
◦ Cross-sectional approach
◦ Longitudinal approach
In cross sectional approach different individuals of
different ages are observed at the same time.
In the longitudinal approach is the like the
prospective method.

13.  Cross sectional approach
◦ For example if we want to
examine age related
changes in dietary intake
of cholesterol among
middle aged adults . Then
in a cross sectional
approach we would study
the dietary pattern of 50
adults at each of three
approximate ages like 35
,45 and 55 year old.
◦ It is less costly in terms
of time and money
 Longitudinal approach
 If we will use
longitudinal approach
then we would study
the same group at the
age of 35, 45 and then
55.
 It is more costly in
terms of time and
money.

14.  The influence of having been born and raised in a
different time is known as cohort effect
 The term cohort refers to a group of people who
have a common demographic factor such as age,
generation or social class.
 This cohort effect can be there in the example
cited above also. Now if we do a cross sectional
study then the diet intake of the older adults in
the age range of 55 year old is very different
from the 35 years old and 45 years old in the
past as well as the current time. So, the cohort
effect can hinder the results
 The best way to do away with the cohort effect is
to combine cross sectional as well as longitudinal
research

15.  Sometimes studies are done on just one
subject . One type of this research is case
study approach.
 In this the researcher constructs a systematic
biography of records of the person’s history ,
interviews and current observation.
 This type of research is used to describe in
depth the development and treatment of an
unusual medical and psychological problem.

16.  This type of research is often used to
demonstrate the usefulness of a new treatment
method for a specific medical or behavioral
problem.
 Data on the subjects problem at the beginning
and at the end of treatment are compared.
 Follow-ups are done at periodic intervals.
 Disadvantage of single subject approach is that
information on only one subject may not describe
what would be found with other individuals.

17.  Genetic Material and Transmission
 Threadlike structures called chromosomes
contain units like genes.
 Genes carry DNA – Deoxyribonucleic acid . It
determines our growth patterns and physical
structures.
 Gene are discrete particles of DNA that are
strung together in chromosome and
transmitted from parent to child.

18.  Each parent contributes half of the genetic
material we inherit.
 Chromosomes have identifying features like
one pair is called sex chromosomes because
they carry the genes that will determine
whether an individual will be male or female.
 Normal sex chromosome for males consist of
one large chromosome (called an X
chromosome) and one small chromosome (y
chromosome).
 Females have two X chromosomes.

19.  Some traits occur in the presence of a single
dominant gene with the paired gene making
little contribution.
 Some traits occur only if two identical genes
make up the pair , these genes are called
recessive genes.

20.  There are two types of twins
◦ Monozygotic twins- or identical twins . They are
conceived together and have the same genetic
inheritance.
◦ Dizygotic twins- they are fraternal twins and they
are not genetically similar.
◦ Most of the research on hereditary factors has
focused on the differences in characteristics shown
in MZ twins as compared with DZ twins.
◦ Investigations using this approach are called twin
studies.

21.  If two individuals in a MZ pair are genetically
similar or identical, we can assume that
differences between them are
environmentally determined.
 Conversely, the greater the similarity between
MZ twins , the more likely it is that the
characteristic is genetically influenced.
 Differences between DZ twins on the other
hand are due to genetic and environmental
factors even when they are the same sex.

22.  If we assume that both the members of each
MZ and DZ pair that we study have had equal
environmental experiences, then we could
measure genetic influence simply by
subtracting the difference from MZ from the
difference for DZ twins.

23.  It compares traits of adopted children with
those of their adoptive parents.
 Adoptive parents contribute greatly to the
rearing of children but are genetically
unrelated to the children , the natural parents
are genetically related to the children
 So, if adopted children are more similar to
their natural parents than to their adoptive
parents , then there is evidence for heredity's
influence.

24.  Heredity affects not only physical characteristics
like height and weight but also the physiological
functions such as heart rate and blood pressure.
 Genetic disorders can produce very high levels of
cholesterol in the blood
 Heredity has its greatest impact on people’
health early in life and by old age the role of
habits and lifestyle becomes increasingly
important.
 Along with genetic factors in cancer,
environmental factors also play an important role

25.  Sickle cell anemia is a hereditary disease
whose victims are usually black people.
 The body of a person who has two of these
genes manufacture large quantities of sickle
shaped red blood cells that carry little
oxygen and tend to clump together in the
bloodstream.
 As a result the vital organs of people with
sickle cell anemia receive inadequate
amounts of oxygen and incur tissue damage.
 It leads to organic failure and brain damage.

26.  It is disease caused due to recessive gene
 In this the baby’s body fails to produce a
necessary enzyme for metabolizing
phenylanine , a toxic amino acid present in
foods.
 If this disease is not treated then the amount
of phenylanine builds up and causes brain
damage.
 Placing PKU babies on special diet low on
phenylanine after birth can prevent this.

27.  These are the genes that can cause cancer.
Researchers have found oncogenes for
cancer, of colon, breast cancer, prostrate
cancer, skin and lung cancer.
 Oncogenes are normal genes or mutations
which result from exposure to harmful
chemical substances such as tobacco smoke.

28.  It is a process in which chemical structures
within or around the DNA govern how, when
and how much a gene acts.
 These structures typically suppress the gene's
usual activity , can change and can be passed
on to offspring.
 Epigenetic operates in normal development
but environmental events can change
epigenetic processes like exposure to toxic
substances , viral infection, dietary elements ,
tobacco, alcohol and drugs.

29.  Research evidence suggests that epigenetic
changes can influence an individual's
response to stress, ability to learn and
remember, and development of health
problems such as cancer.

30.  The combination of experimental and non
experimental is the best.
 For example if we want to study that whether
people’s reading information about the health effects
excessive cholesterol would induce them to modify
their diets we could manipulate the independent
variable by having the experimental group but not
the control group read the health information.
 If the researcher is interested in finding out the age
related differences that whether its easy to persuade
a group of 50 years of age and 20 years of age. The
researcher would randomly assign the people into
two groups according to the age and then examine
their diet and blood cholesterol level.