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Published by nurm1605, 2019-04-15 04:11:01

research design_merge pdf




List of Content

• Cohort
• Prospective
• Retrospective
• Cross sectional
• Longitudinal
• Randomized control trial


• Research design

• Cohort
• Prospective
• Retrospective
• Cross sectional
• Longitudinal
• Randomized control trial

• Cohort study
• The word cohort means a group of people. These types of studies look at groups of people.

They can be forward-looking (prospective) or backward-looking (retrospective).

• Prospective" studies are planned in advance and carried out over a future period of time.
• Retrospective cohort studies look at data that already exist and try to identify risk factors for

particular conditions. Interpretations are limited because the researchers cannot go back
and gather missing data.

• The cohort study design is the best available scientific method for measuring the effects of a
suspected risk factor..

• Cohort study
• outcome is measured after exposure
• yields true incidence rates and relative risks
• may uncover unanticipated associations with outcome
• best for common outcomes

• expensive
• requires large numbers
• takes a long time to complete
• prone to attrition bias (compensate by using person-time methods)
• prone to the bias of change in methods over time

• Prospective study
• A prospective study watches for outcomes, such as the development of a disease, during the

study period and relates this to other factors such as suspected risk or protection factor(s).

• The study usually involves taking a cohort of subjects and watching them over a long period.
• The outcome of interest should be common; otherwise, the number of outcomes observed

will be too small to be statistically meaningful (indistinguishable from those that may have
arisen by chance).

• All efforts should be made to avoid sources of bias such as the loss of individuals to follow
up during the study.

• Prospective study
• Sometimes called as prospective cohort study
• participants are enrolled into the study before they develop the disease or outcome
• Prospective studies typically last a few years .Recommended 5 years
• Study participants typically have to meet certain criteria to be involved in the study. For

example, they may have to be of a certain age, profession, or race. Once the participants are
enrolled, they are followed for a period of time to see who gets the outcome in question
(and who doesn’t). Usually, the research is conducted with a goal in mind and participants

are periodically checked for progress, using the same data collection methods and questions
for each person in the study. Follow ups might include:

• Email questionnaires,Phone, internet, or in-person interviews, Physical exams, Imaging or
laboratory tests.

• Example
• Example
• Relative risk
• COnclusion RR
• If the RR<1 then the exposed group have less risk in developing disease
• If RR>1 then the exposed group have more risk in developing disease
• If RR=1 the exposed group have almost equal risk (no difference) with unexposed group in

developing disease

• Retrospective study
• A retrospective study looks backwards and examines exposures to suspected risk or

protection factors in relation to an outcome that is established at the start of the study.

• Most sources of error due to confounding and bias are more common in retrospective
studies than in prospective studies.

• Retrospective study
• In retrospective cohort studies, two groups are retrospectively identified and compared
• A cohort of healthy subjects is subdivided into two groups – one exposed to a given factor

and the other nonexposed to the same factor

• Advantage and disadvantage
• The advantages of retrospective cohort studies are that they are less expensive to perform

than cohort studies and they can be performed immediately because they are retrospective.

• their limitation is: poor control over the exposure factor, covariates, and potential

• Case control study
• outcome is measured before exposure
• controls are selected on the basis of not having the outcome
• good for rare outcomes
• relatively inexpensive
• smaller numbers required
• quicker to complete
• prone to selection bias
• prone to recall/retrospective bias
• Analysis:, chi-square 2 by 2 test, Fisher's exact test, logistic regression.
• Case control study
• Cases should be selected based on objective inclusion and exclusion criteria from a reliable

source such as a disease registry.

• Regardless of how the cases are selected, they should be representative of the broader
disease population that you are investigating to ensure generalisability.

• As such, controls should also be selected carefully. It is possible to match controls to the
cases selected on the basis of various factors (e.g. age, sex) to ensure these do not confound
the study results.

• Case-control studies are retrospective.
• Case control study
• Odds ratio
• Conclusion odds Ratio
• = 1 – indicates no association

> 1 – indicates a positive association
< 1 – indicates a negative association

• OR=0.26 The odds of developing disease is low compare those who is not vaccinated
• Differences between cohort and case control study
• A cohort study is a research design where the researcher studies a group of people, also

known as a cohort, for a longer period of time.

• On the other hand, a case-control study is a research design used by researchers where the
research begins with an outcome to comprehend the cause

• Both exposure and outcome (Disease) have occurred before the start of the study.(case
The study proceeds backward from effect to cause (case control)

• It uses a control or comparison group to support or refute an inference.(case control)

Differences between cohort and case control study

• Cross sectional study

• Cross-sectional studies collect all data at a set point in time. This allows the researcher to
assess the prevalence of a disease or of other variables of interest.

• Is an observational study
• Suitable to find relationships between variable
• For example
• relationship between daily walking , glucose level, BMI and cholesterol levels among

residence in KL

• example

• Longitudinal study
• Researchers conduct several observations of the same subjects over a period of time,

sometimes lasting many years.

• Observational study
• Follow up among the same sample(subjects)
• For example
• To determine the change in cholesterol levels among women over 40 who walk daily for a

period of 2 years

• example
• Randomized control trial
• A study design that randomly assigns participants into an experimental group or a control


• As the study is conducted, the only expected difference between the control and
experimental groups in a randomized controlled trial (RCT) is the outcome variable being

• Randomized controlled trials
• There are two groups,
• 1)one treatment group and one control group. The treatment group receives the treatment

under investigation, and the control group receives either no treatment (placebo) or
standard treatment.

• 2) Patients are randomly assigned to all groups.
• To answering questions about the effectiveness of different therapies or interventions.
• Randomization helps avoid the bias in choice of patients-to-treatment that a physician might

be subject to.

• Example

• tips
• To decide which research design depending on objective of the study
• Limitation of your study
• Inclusion and exclusion criteria
• references


• Haynes, S. G., & Feinleib, M. (1980). Women, work and coronary heart disease: prospective
findings from the Framingham heart study. American Journal of Public Health, 70(2), 133-


• De Groot, L. C., Verheijden, M. W., De Henauw, S., Schroll, M., & Van Staveren, W. A. (2004).

Lifestyle, nutritional status, health, and mortality in elderly people across Europe: a review

of the longitudinal results of the SENECA study. The Journals of Gerontology series A:

Biological sciences and Medical sciences, 59(12), 1277-1284.

• Kirchengast, S., & Haslinger, B. (2008). Gender differences in health-related quality of life
among healthy aged and old-aged Austrians: cross-sectional analysis. Gender Medicine, 5(3),


• Robinson, T. N. (1999). Reducing children's television viewing to prevent obesity: a
randomized controlled trial. Jama, 282(16), 1561-1567.

• Natour, J., Cazotti, L. D. A., Ribeiro, L. H., Baptista, A. S., & Jones, A. (2015). Pilates improves
pain, function and quality of life in patients with chronic low back pain: a randomized

controlled trial. Clinical rehabilitation, 29(1), 59-68.

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