The design and planning
phase:
Types of study designs
(quantitative designs)





Intervention
intervention
(Experimental)
experimental )
Explanatory
Descriptive
(Exploratory)
No
( non
Observational
(analytic)
( non experimental )




Descriptive
Observational
(analytic)
(Exploratory)
Cohort
(prospective)
case report
Case control(retrospective)
case
series
Cross sectional(no follow up)
Types of study designs
1- Non intervention Studies
In which the researcher just observes and
analyses researchable objects or situation
but does not intervene
2-Intervention studies
In which the researcher manipulates
objects or situations and measures the
outcome of his manipulations
1. Exploratory studies 
 An exploratory study is a small-scale
study of relatively short duration,
which is carried out
when little is known about a situation or
problem. It may include description as
well as
comparison.
For example:
 A national AIDS Control Programme wishes
to establish counseling services for HIV
positive and AIDS patients, but lacks
information on specific needs patients have
for support. To explore these needs, a
number of in-depth interviews are
held with various categories of patients (males,
females, married and single) and with some
counselors working on a programme that is
already under way.

When doing exploratory studies we describe
the needs of various categories of patients and
the possibilities for action. We may want to go
further and try to explain the differences we
observe (e.g., in the needs of male and female
AIDS patients) or to identify causes of
problems. Then we will need to compare
groups

Descriptive studies:
Descriptive studies may be defined as
studies that describe the patterns of
disease occurrence and other healthrelated conditions by person place and
time.






Personal variables include: basic
demographic factors, such as age, sex
marital status or
occupation, as well as the consumption of various
types of food or medication use.
Characteristics of place refer to the geographic
distribution of disease, including variation
among countries or within countries, such as
between urban and rural areas.
With regard to time, descriptive studies may
examine seasonal patterns in disease onset,
Uses of descriptive studies
 They can be done fairly quickly and easily.
 Allow planners and administrators to
allocate resources
 Provide the first important clues about
possible determinants of a disease (useful
for the formulation of hypotheses
Types of descriptive studies

A-Individuals . case reports 
Descriptive studies
. 
case series
. cross-sectional 
B-Populations . ecological 
(correlational) 
a) Case reports and case series
 Case report: a careful, detailed report
by one or more clinicians of the profile of
a single
 patient.
 The individual case report can be
expanded to a case series, which
describes characteristics
 of a number of patients with a given
disease.

Uses
 Important link between clinical medicine
and epidemiology
 One of the first steps in outbreak
investigation
 Often useful for hypothesis generating
and examining new diseases, but
conclusions
about etiology cannot be made.
Examples
Grudeva popova et al .2007 described
acase of 47-years-old woman developed
therapy related leukemia after radioiodin
treatment for thyroid carinoma.The
patient was treated with chemotherapy &
achieved complete response lasting for 3
years
 ( case report)

2-In November 2005 tan et al described 5
cases of bacteremia with
Arcanobacterium hemolytic in association
with soft tissue infection from immuno
competent .they also review the literature
about such rate condition in human
specially in D.M
 ( CASE REPORT)

case series
3- Oliver at el 2007 .Reviewed all cases
presenting with extra-tubal presenting with
extra-tubal pregnancy in their institution
including seven interstitial ,2 cervical ,three
ovarian &2 abdominal pregnancy .They found
that both clinical finding &imaging modalities
are essential to make an accurate diagnosis
.Treatment with minimal access technique
,non-invasive radiological procedure or
medical treatment should encourage
Ecological studies:( correlational )
 data from entire populations are used to
compare disease frequencies between
different groups during the same period
of time or in the same population at
different points in time.

Example: Countries with low cigarette
consumption have lower lung cancer rates
than those countries with high cigarette
consumption.
 Ecological studies are usually quick and
easy to do and can be done with already
available information.

Since ecological studies refer to whole
populations rather than to individuals, it is
not
possible to link an exposure to occurrence
of disease in the same person.

II. Analytic studies
(Observational)
Analytic studies may be defined as studies
used to test hypotheses concerning the
relationship between a suspected risk
factor and an outcome and to measure
the magnitude of the association and
its statistical significance.

Observational studies
*No human intervention involved in
assigning study groups; simply observe the
relationship between exposure and
disease.
* Subject to many potential biases, but by
careful design and analysis, many of these
biases can be minimized.
Examples of observational studies:
comparative cross-sectional, cohort and
case control studies.
(A) Cross-)No follow up)
sectional studies
involve the collection of data at one
point in time: the phenomena under
study are captured during one period of
data collection.
 Cross-sectional studies are appropriate
for
describing the status of phenomena or for
describing relationships among
phenomena at a fixed point in time.

For example,
 we might be interested in determining
whether psychological symptoms in
menopausal women are correlated
contemporaneously with physiologic
symptoms.

Cross-sectional designs are sometimes used
for time-related purposes, but the results
may be ambiguous.
For example, we might test the hypothesis,
using cross-sectional data, that a determinant
of excessive alcohol consumption is low
impulse control, as measured by a
psychological test. When both alcohol
consumption and impulse control are
measured concurrently, however, it is
difficult to know which variable influenced the
other, if either.


The main advantage of cross-sectional
designs in such situations is that they are
practical: they are easy to do and are
relatively economical
Example of a cross-sectional studY





Example of a cross-sectional study:
Mindell and Jacobson (2000) assessed sleep
patterns and the prevalence of sleep
disorders during pregnancy. With a crosssectional design, they compared women who
were at four points in pregnancy:
8 to 12 weeks, 18 to 22 weeks; 25 to 28
weeks; and 35 to 38 weeks. They concluded
that sleep disturbances were especially
common in late pregnancy.
b) Cohort )Prospective design)
studies
starts with a presumed cause and then
goes
forward in time to the presumed effect.
For example, we might want to test the
hypothesis that the incidence of rubella
during pregnancy (the independent
variable) is related to infant abnormalities
(the dependent variable

Cohort studies: Study groups identified
by exposure status prior to ascertainment
of their disease status and both exposed
and unexposed groups followed in
identical manner until they develop the
disease under study, they die, the study
ends, or they are lost to follow up

Example of a prospective non experimental
study:
Brook, Sherman, Malen, and Kollef (2000)
conducted
 a prospective cohort study to examine
 clinical and cost outcomes of early versus
late tracheostomy in patients who require
prolonged mechanical ventilation. Early
tracheostomy was found to be associated
with shorter lengths of hospital stay and
lower hospital costs.

Strengths and limitations of
the cohort study design
Strengths:
 Is of particular value when the exposure
is rare
 Can examine multiple effects of a
single exposure
 Allows direct measurement of incidence
of disease in the exposed and nonexposed
 groups.

Limitations:
 Is inefficient for the evaluation of rare
diseases
 Expensive and time consuming
 Validity of the results can be seriously
affected by losses to follow-up.

c) Case-control
studies(Retrospective)


Group of subjects with the disease (cases)
and group of subjects without the disease
(controls) are identified. Information, about
previous exposures are obtained for cases
and controls, and frequency of exposure
compared for the two groups. OR
are ones in which a phenomenon existing
in the present is linked to phenomena that
occurred in the past, before the study was
initiated.
Example of a retrospective study:

Heitkemper, Jarrett, Taylor, Walker,
Landenburger, and Bond (2001) used a
retrospective design in their study of
factors contributing to the onset of
irritable bowel syndrome (IBS). They
compared samples of women with and
without IBS in terms of their history of
physical abuse, and found that abusive
experiences were more prevalent among
women with IBS
Strengths and limitations of
the case-control study design
Strengths:
 Is relatively quick and inexpensive
 Is optimal for the evaluation of rare
diseases.
 Can examine multiple etiologic factors for
a single disease

Limitations:
 Is inefficient for the evaluation of rare
exposures
 Cannot directly compute incidence rates
of disease in exposed and non- exposed
individuals.
 Is particularly prone to bias compared
with other analytic designs, in particular,
selection and recall bias.

Intervention studies
In intervention studies, the researcher 
manipulates a situation and measures the
effects of this manipulation. Usually (but
not always) two groups are compared,
one group in which the intervention takes
place (e.g. treatment with a certain drug)
and another group that remains
‘untouched’ (e.g. treatment with a
placebo).
The two categories of intervention
studies are:
 Experimental.
 Quasi-experimental.

1. Experimental studies
Experiment: A research study In which the
investigator controls [manipulates] the
independent variable and randomly
assigns subjects to different conditions.
experimental design is characterized
by
the following properties:
• Manipulation—the experimenter does something 
to at least some subjects 
• Control—the experimenter introduces controls 
over the experimental situation, including the use 
of a control group
• Randomization—the experimenter assigns 
subjects
to a control or experimental group on a random 
basis
Types of experimental design:
1. Basic experimental designs
 A simple design that is sometimes
referred to as and after only design or a
posttest only design because data on the
dependent variable are only collected
once-after the experimental treatment
has been introduced. When data are also
collected before treatment (i.e., at
baseline), the design is a before-after or
pretest-posttest design

For example testing hospitalized

children’s affective behavior after being
cared for by nurse wearing differentcolored uniforms.
2. Solomon four-group design
 When data are collected both before and
after an intervention, the pretest (initial)
measure sometimes has the potential to
distort the results. That is, the posttest
measures may be affected not only by the
treatment but also by the exposure to the
pretest.


For example which consists of two
experimental groups and two control
groups. One experimental group and one
control group would be administered the
pretest and the other groups would not,
thereby allowing the effects of the pretest
measure and intervention to be
segregated.
3. Factorial design
 When a research manipulates more than
one variable at a time the design is known
as factorial experiment. Factorial designs
permit testing of both main effects
(effects resulting from the experimentally
manipulated variables) and interaction
effects (effects resulting from combining
the treatments).


For example Suppose that we were
interested in comparing two therapeutic
strategies for premature infants: one method
involves tactile stimulation, and the second
approach involves auditory stimulation. At
the same time, we are interested in learning
if the daily amount of stimulation is related
to the progress of the infant. The dependent
variables for the study will be various
measures of infant development, such as
weight gain, cardiac responsiveness, and so
forth.
4. Repeated measures deign
 In repeated measures (crossover)
designs, one group of subjects is exposed
to two or more conditions in random
order, thereby allowing subjects to severe
as their own controls. In which the
subjects who are randomly assigned to
different treatments are different people.


For example the infants exposed to 15
minutes of auditory stimulation were not
the same infants as those exposed to the
other five possible treatment conditions.
A repeated measures design (sometimes
called a crossover design) involves the
exposure of the same subjects to more
than one experimental treatment.
5. Randomized clinical trails
 When an experimental design is used to
tests the efficacy of a clinical treatment in
a large, heterogeneous population, the
study is often referred to as a clinical trail.
Clinical trails typically use either a beforeafter or an after-only design



For example, for evaluating a promising
new drug for the treatment of AIDS,
researchers may randomly allocate 75% of
the subjects to the experimental group
and 25% to the control group.
2-Quasi-experimental

Quasi-experimental: A study in which
subjects are not randomly assigned to
treatment conditions, but the researcher
does manipulate the independent variable
and exercises certain controls to enhance
the internal validates of the results
Types of quasi-experimental
a. Non-equivalent groups or static
groups design
 Two receive different treatments, but are
not randomly assigned or matched to
conditions. Eliminates history effects but
not subject effects.


Example: Participants may be given the
choice of which therapy to receive. The
potential participants most likely to benefit
from the new therapy are assigned to that
condition. Intact (already existing or static)
group may also be used, for example, all the
clients in an existing therapy group may be
given the new therapy. If the group receiving
the new therapy improves more than the
control group, we can be somewhat more
confident in the benefits of the new therapy.
b.Time-series design
 There is one group of research
participants with several baseline
measures, “a treatment and at least one
more measurement eliminates subject
effects but not history effects.


Example: One group of research
participants is selected. Their mental
health is measured each month for
several months. Then they are given the
new therapy and measured again
Qualitative design:


Qualitative research: The investigation
of phenomena, typically in an in depth and
holistic fashion, through the collection of
rich narrative materials using a flexible
research design.
Qualitative research types
1-Phenomenology: a form of qualitative
research in which the researcher
attempts to understand how one or more
individuals experience a phenomenon.
For example, you might interview 20 
widow and ask them to describe their
experiences of deaths of their husbands
2-Ethnography: is the form of qualitative
research that focuses on describing the
culture of a group of people.
For example, you might decide to go and 
live in a Mohawk communities and study
the culture and their educational
practices
3-Case study research: is a form of 
qualitative research that is focused on
providing a detailed account of one or
more cases.
For example, you might study a 
classroom that was given a new
curriculum for technology use.
4-Grounded theory: is a qualitative
approach to generating and developing a
theory form data that the researcher
collects.
 For example, you might collect data
from parents who have pulled their
children out of public schools and develop
a theory to explain how and why this
phenomenon occurs, ultimately
developing a theory of school pull-out
5-Historical research: research about
events that occurred in the past.
 For example, you might study the use of
corporeal punishment in schools in the
19th century.

Mixed research methods:
It is a general type of research “it’s one of
the three paradigms” in which
quantitative and qualitative methods are
mixed in one overall study.
 i.e. it is research in which the researcher
uses the qualitative research paradigm for
one phase of a research study and the
quantitative research paradigm for
another phase of the study.


For example, a researcher might
conduct an experiment (quantitative) and
after the experiment conduct an
interview study with the participants to
see how they viewed the experiment and
to see if they agreed with the results.