STUDY DESIGN

SiswantoDepartment of Public Health

Faculty of MedicineUniversity of Brawijaya

OVERVIEW STUDY DESIGNS

• The difference between interventional (experimental) study and observational study

An interventional or experimental study is when the investigator test whether modifying or changing something about study participant (risk factor) alter the development of the outcome (disease)

• The essence of an interventional study is that the investigator has the power to randomly assign exposure in a way that enhances the validity of a study (Investigator determine who exposed or not exposed)

• Observational studies involve the investigator collecting data on factors (exposures) associated with the occurrence of the outcome of interest, without attempting to alter the exposure status of participant (no control over exposure)

• The investigator does not intervene or manipulate the situation

• Since the investigator does not control the circumstances of the exposure, a simple comparison of exposed and not exposed will not accurately reflect the effect of the exposure if those who are exposed differ from those who are unexposed in other ways that are related to the outcome

• Observational studies : descriptive (without control group), analytic (with control group ) : cross-sectional, case-control study and cohort study.

RESEARCH DESIGN

OBSERVATIONAL STUDIES (NO CONTROL OVER EXPOSURE)

NO COMPARISON GROUP

THE RESEARCH

INTERVENTIONAL STUDIES (INVESTIGATOR DETERMINE WHO EXPOSED

OR NOT EXPOSED)

ANALYTIC

CASE REVIEW SURVEILLANCE SURVEY CROS SEC TIONAL STUDY

CASE CONTROL STUDY

COHORT STUDY

DESCRIPTIVE

COMPARISON GROUP

SCHEME FOR RESEARCH CYCLE

DESCRIPTIVE STUDIES

MODEL BUILDING FORMULATION OF

HYPOTHESIS

ANALYSIS OF RESULTS, SUGGEST FURTHER-DESCRIPTIVE AND NEW HYPOTHESIS

ANALYTICAL STUDIES

- X - SECTIONAL

- CASE-CONTROL STUDY

- COHORT

- CLINICAL TRIALS

- FIELD TRIALS

EXPERIMENTAL STUDIES :

TEST HYPOTHESIS

DESCRIPTIVE STUDIES

• The activities related to characterizing the distribution of diseases (time, person and place) within population

• Information is collected only on those individuals with a health problem or a particular exposure. There is no comparison group. Much useful information can be derived from these studies but no definite analysis of cause-effect association can be made from these information

• Descriptive studies are used by public health specialist and health provider for the surveillance of communicable disease or non-communicable disease, to decide on the allocation of resources and to plan prevention or health promotion programmes ( Grimes and Schulz 2002)

• Epidemiologist also undertake descriptive studies to identify clues as to possible determinants of diseases or risk factors and to formulate of hypothesis

ANALYSES BY TIME

• The frequency of diseases, health events or risk factors may increase, decrease or stay constant over time

• Disease rates change over time. Some of these changes occur regularly and can be predicted

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Comparison of the incidence of tuberculosis among migrants who moved from high to low risk countries with the incidence in the general population of the adopted country

ANALYSES BY PLACE

We describe a health event by place to gain insight into the geographical extent of the problem.

For place, we may use place of residence, birthplace, place of employment, hospital unit, urban and rural etc, depending on which may be related to the occurrence of the health event or disease

Example : diseases that are passed from one person to another spread more rapidly in urban areas than in rural ones, because the greater crowding in urban areas provides more opportunities for susceptible people to come into contact with some one who is infected.

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ANALYSES BY PERSON

When we organize or analyze data by “person” there are several person categories.

Inherent characteristics of people ( age, race, sex), acquired characteristics ( immune, marital status), their activities ( occupation, use of tobacco, drugs), the conditions under which they live ( socioeconomic, access to medical care)

• Example : Sex• For some disease, this sex-related difference is

because of genetic, hormonal, anatomic, or other inherent differences between the sexes.

• Premenopausal women have a lower risk of heart disease than man of the same age. This difference is attributed to higher estrogen level in women.

New smear-positive case notification by age and sex (2005)

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Number of reported cases of tuberculosis by age in the United States 2002

Toll-like receptor 2 genotypes and clinical types of tuberculosis (TB) disease (Ogus et al., 2004) Type of TB Subjects Genotype n(%) AA GA GG Pulmonary 129 (85.4) 11 12 106Lymphadenitis 8 (5.3) 2 1 5Pleural 10 (6.6) 10Pulmonary andLymphadenitis 2 (1.3) 1 1Bone 1 (0.7) 1Renal 1 (0.7) 1• A: adenine; G: guanine

CROSS-SECTIONAL STUDIES

A cross-sectional studies (prevalence study) describes the frequency of particular attribute such as a specific exposure , disease or other health-related event in a defined population or a sample of a population  at a given point in time 

CROSS SECTIONAL STUDIESThe comparison is made between a group of persons who has the disease and a group that does not have the disease, but the characteristic and/ or exposure of the two groups are observed in the same time

D+ D- TOTAL

FR + A B A+B

FR - C D C+D

TOTAL A+C B+D A+B+C+D

CROSS-SECTIONAL-STUDY

TARGET POPULATION

STUDY SAMPLE

COMPARE

STUDIED CHARACTERISTICSTUDIED CHARACTERISTIC

D+ D-

SAMPLING

Study Process

1. Statement of the research question or hypothesis.2. Research variable identification : Operational definition of risk factor (independent

variable) and disease ( dependent variable)3. Assessment of risk factor and disease : Interview, physical examination, laboratory test,

special procedures , medical record.

4. Analysis of data

Prevalence ratio = A/(A+B):C/(C+D)

D+ D- TOTAL

FR + A B A+B

FR - C D C+D

TOTAL A+C B+D A+B+C+D

ADVANTAGES

1 Quick and easy to perform

2 Losses to follow up –

3 Can be used to investigate many exposures

and outcomes

DISADVANTAGES

1 Difficult to interpret association in terms of cause and effect (Problem with direction of causality/reverse causality

2 Not suitable for the rare disease, since sample size requirement will have to be large

3 Not suitable for diseases of short duration

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EpileptologyVolume 1, Issue 1 , Pages 55-60, March 2013

Costs of epilepsy and their predictors: Cross-sectional study in Germany and review of literature

• The aim of this cross-sectional study was to quantify epilepsy-related costs in Germany and to identify cost-driving factors. In addition, we reviewed recent studies on costs of epilepsy and put the present results in an international perspective.

• Conclusion Indirect costs remained higher than direct costs in this

study conducted in primary care sector and at an epilepsy center in Germany. Our study and other recent studies with a top-down approach demonstrated hospitalization beside AED costs as an important direct cost factor.

CASE-CONTROL STUDY

THE STUDY MOVE BACKWARD FROM DISEASE ( EFFECT) TO RISK FACTOR (CAUSE).PERSON WITH AND WITHOUT DISEASE ARE IDENTIFIED AND THEN THE PRESENCE OR ABSENCE OF PREVIOUS EXPOSURE TO THE RISK FACTOR IS DETERMINED

scheme of case-control study

select cases select appropriate controls

obtain information about previous exposure to proposed risk of factors each group

compare the frequency of exposure between the two group

STUDY PROCESS

1 Selection of cases . Clearly define case definition . Should be incidence cases . Representative of total cases.2 Selection of controls . Should be representative of the population from which the cases come . Be sure that the risk factor under study is not also related to disease among control group

3. Sources of cases and controls Cases : Hospital, Community, Registration or surveillance system Controls : Hospital, Community, relative of cases, Neighbors4. Assessment of exposure to risk factor . Should be ascertain in the similar procedure between cases and controls. . Use record or documents as much as possible ( The goal is to obtain as accurate information as possible about

each individuals exposure to the main risk factors) . Clearly define exposure to risk factor

5. Try to minimize bias . From selection of cases and controls : Selection bias . From data collection about risk factor exposure : memory bias (information bias) . From data analysis : Confounding bias

Method of data analysisOdds ratio : Odds of cases : odds of controls

A/(A+C) B/(B+D)= : C/(A+C) D/(B+D)

= A/C:B/D=AD/BC

D+ D-

FR + A B

FR - C D

W ------ Both Case and Control exposed X-------- Case exposed but control unexposedY-------- Case unexposed but control exposedZ-------- Both case and control unexposedW and Z Concordant pairsX and Y discordant pairsOdds Ratio = X/Y

Control Exposed

Control Unexposed

Total

Case Exposed W X W+X

Case Unexposed

Total

Y

W+Y

Z

X+Z

Y+Z

W+X+Y+Z

ADVANTAGES

1 Efficient for the study of rare diseases2 Efficient for the study of chronic disease (diseases

with a long latency)3 Tend to require a smaller sample size than other

designs.4 Less expensive than other designs

5 Many risk factors can be studied simultaneously

DISADVANTAGES1. The temporal sequence between exposure

and outcome may be difficult to establish (with come first : exposure or disease ?)

2. Obtaining valid information about past exposures may be difficult ( recall bias)

3. Selection of an appropriate control group may be difficult (selection bias)

4. Not suitable for investigating rare exposures ( unless a large proportion of cases are attributable to that exposure)

Table.5 Distribution of the TLR2 polymorphism and odds ratios in the study and control groups (Ogus et al., 2004)

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Cardiovascular Risk Factors in North Indians: A Case-Control Study

The study move forward from risk factor (cause) to disease (effect).Population exposed and not exposed to a risk factor are identified and then both population were followed to determine the frequencies of health problems.

COHORT STUDY

population

Risk factors +

Risk factors -

Disease +

Disease +

Disease -

Disease -

STUDY DESIGN OF COHORT

STUDY PROCESS1 Selection of studied cohort . Total population, divided by risk factor exposure . Special group who possessed certain characteristics or exposure such as

doctors . Risk or exposure group, those who

receives risk factor such as industrial workers. . From survey for special group : DM, hypertension

2. Selection of comparison group or control group without risk factor from

. General population . Sample population without risk factor3. Make sure that both exposure and non

exposure group do not have the disease of interest before the study begins

4. Data collection Risk factors : records, medical

examination, measures of the environment, questionnaireProblem : effect - changes in exposure

Information on outcome/effect : periodic/non periodic medical examination, surveillance of death certificate.Problem : losses to follow-up

5.Method of data analysisRELATIVE RISK = A/ (A+B) : C/ ( C+D

)D+ D-

FR + A B

FR - C D

ADVANTAGES

• Direct calculation of relative risk• May yield information on the incidence of disease• Clear temporal relationship between exposure and

disease• Particularly efficient for study of rare exposure• Can examine multiple effect of a single exposure

• Minimizes bias• Strongest observational design for establishing

cause and effect relationship

DISADVANTAGES

• Time consuming• Often requires a large sample size• Expensive• Not efficient for the study of rare diseases• Lost to follow-up• Changes in exposure• Ethic

A cohort study of infant feeding practices in city, suburban and rural areas in Zhejiang Province, PR China

Liqian Qiu†1,2, Yun Zhao†2, Colin W Binns*2, Andy H Lee†2 and Xing Xie†1

Address: 1Women's Hospital, School of Medicine, Zhejiang University, PR China and 2School of Public Health, Curtin University, WA, Australia

Published: 3 March 2008International Breastfeeding Journal 2008, 3:4

Background:

Breastfeeding is the basis for appropriate nutrition for infants and is strongly supported by the Ministry of Health in China. However, there are differences in infant feeding practices in different areas of the country. The aim of this study was to compare the infant feeding practices and the prevalence of determinants of initiation and continuing to breastfeed until six months of age in city, suburb and rural areas in Zhejiang Province, PRC.

Methods: A longitudinal cohort study of infant feeding practices was

undertaken in city, suburban and rural areas in 2004/2005. Mothers were recruited and interviewed before discharge from hospitals. A total of 1520 mothers were recruited into the study. Follow-up interviews were administered at 1, 3 and 6 months after birth to obtain details of infant feeding practices.

Results: Any breastfeeding' rates were high before discharge at all three

locations, 96.5% in city, 96.8% in suburb and 97.4% in the rural area. The 'exclusive breastfeeding' rates in the city, suburban and rural areas before discharge were 38.0%, 63.4% and 61.0% respectively. By sixth months the 'any breastfeeding' rates had declined to 62.8%, 76.9% and 83.6% and the 'exclusive breastfeeding‘ rates had fallen to 0.2%, 0.5% and 7.2% in city, suburb and rural areas respectively. There were

differences in feeding practices between the three locations, including the use of prelacteal feeds and the introduction of supplementary feeds.

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research methods. Investigation, Measurement and analysis. England. Open University Press.

Norman Vetter and Ian Mathews (2006) . Epidemiology and Public Health Medicine.

Raymond S, Stephen R. Daniels, W. Dana Flanders (2005). Medical Epidemiology.

Mark Elwood (1998). Critical Appraisal of Epidemiological Studies and Clinical trials. Second Edition. Oxford University Press

Robert H. Fletcher, Suzanne W. Fletcher and Edward H. Wagner. Clinical Epidemiology. The Essentials. Second Edition.

Diederick E. Grobbee and Arno W. Hoes (2009). Clinical Epidemiology. Principles, Methods, and Application for Clinical Research.

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GOOD LUCK !