Dr. Dalia El-ShafeiLecturer, Community Medicine Department,

Zagazig Universityhttp://www.slideshare.net/daliaelshafei

Epidemiology is derived from the Greek,

Epi: On or upon. Demos: people. Logos : the study of

Epidemiology is the basic science

of Public Health

Definition of EpidemiologyThe STUDY of the DISTRIBUTION and DETERMINANTS of HEALTH-RELATED STATES in specified POPULATIONS, and the application of this study to CONTROL of health problems."

Is the basic science of public health

Provides insight regarding the nature, causes, and extent of health and disease

Provides information needed to plan and target resources appropriately

So, Epidemiology

Non-experimental studies = Observational studies:

-Investigator does not intervene.

-The investigator observes natural course of events, observing who is exposed and who is not, who is diseased and who is healthy.

-The non-experimental studies can be either descriptive or analytical.

Experimental studies = Interventional studies:

- Involve an active trial to change disease determinant by the investigator who controls the exposure.

-Investigator allocates the exposure and follows the subjects.

- Participant are identified on the basis of their exposure status and followed to determine whether they develop the outcome or not.

Epidemiological methods

Descriptive Epidemiological studies

To Know the situation: (what is the problem? What are its manifestations?)

Or To describe the general characteristics

of a disease /or health problem in relation to (time – place –person).

□ Person: Who is getting sick?□ Place: Where is the sickness occurring?□ Time: When is the sickness occurring?

PPT = person, place, time

Descriptive Studies

1- Case Report:

Example:Intestinal obstruction was reported in a young child.. Documents

showed that this child received Rota virus vaccine three months ago. A

detailed report about this unusual event and exposure was published

in a medical journal. The investigator formulated a hypothesis that

Rota virus vaccine may have been responsible for the rare occurrence

of this event.

The features of the Case Report:

It consists of a careful and detailed report (published

in medical journals) by one or more clinicians of

unusual medical condition.

It represents the first clue in the identification of a

new disease.

It leads to formulation of a new hypothesis.

2-Case Series:

It is the only study which depends on Routine Surveillance. What is surveillance?

Example of the case series study:

•During 1950 , 8 cases of cancer lung were admitted to different

hospitals during the same period of time. Taking history from these

patients showed that they were miners . This unusual circumstance

suggested that the miners may been exposed to something. Investigating

this circumstance showed high concentration of radon gas. A hypothesis

was formulated that lung cancer is related to exposure to radon.

The benefits of case report & case series:They identify a new case and/ or an unusual variation of a disease occurrence.

•They formulate a new hypothesis for disease occurrence. •They act as trigger as they stimulate the start of analytic studies to be conducted to identify the risk factors of the disease.•Modification of the case series to be a case control study can be obtained by using a comparison group.

The limitations of the case report & case series:

For the case report, the presence of any exposure may be coincidental because it is based on a single experience .

Lack of the comparison group in case series can either obscure the relationship or suggest an association which is not actually exist.

Both of them cannot be used to show the causal association, i.e. can not be used to test the hypothesis.

3-Correlation study: ( Ecological study)

The source of data is the entire population . It compares disease frequencies:

- between different population during the same period of time Or - In the same population at different in time .

It compares 2 quantitative variables.

Correlation between one of climatic indicator (Temp.) & frequency of cerebrovascular storks.

Figure 1 shows the correlation between the average regional temp. & the frequency of CVSs in different countries. Countries with the highest average temp. have the highest rates of CVSs and vice versa.

100 The average regional temp. & the frequency of CVSs

80

+ve Correlation (r = +1) 60

40

20

0 10°C 15°C 20°C 25°C 30°C 35°C 40°C

The Average Regional Temperature

Example 2:

The average number of mammography carried for

women above 50 years of age per year & the

mortality from cancer breast.

This can be presented by the following figures.

The average number of mammography per year for woman

above 50 & the mortality from cancer breast

100 Negative Correlation (r = -1)

80 60

40

20

0 3 4 5 6 7 8 9

The average number of mammography per year for woman above 50

The advantages of the correlation study:

1- Formulates new hypothesis.

2- Quick & Cheap.

The limitations of correlation studies:1.As the value of exposure is quantified by the average, it is impossible to link the exposure & the disease in a particular individual. It is not possible to tell that the person who gets cerebro-vascular stroke is the one who is exposed to high temperature.

2. They cannot be used for testing the hypothesis.

3.Lack of the ability to control for the effects of the confounding factors.

Confounding factors:

These are factors other than the studied one that disturb the relation between the studied exposure and the disease of interest. For example: The association between the average family size and the frequency of iron deficiency anemia may be due to other factors such as the pattern of diet, the infectious diseases , the socioeconomic conditions and parasitic infections.

Impacts of the Confounding Factors

Large Family size (Exposure)

Iron deficiency anemia (condition)

Parasitic InfectionPattern of Diet

Mothers AwarenessMothers Education

(Confounding factors)

4- Cross sectional study (Prevalence study):

Population Sample

Without Exposure & without disease

Without Exposure & with disease

With Exposure &without disease

With Exposure & with disease

Example:

During the year 2004 , a representative sample of secondary school pupils in a city x (n=400) were asked about consumption of high caloric diet & examined to detect obesity. Questions:Draw the flow chart.Tabulate the data.Write the title of the table.

No consumption of high Caloric diet without obesity

n=304

No consumption of high Caloric diet with obesity

n=16

Consumption of high Caloric diet without obesity

n=60

Consumption of high caloric diet with obesity

n=20

Secondary school pupils

Samplen=400

The flow Chart:

Distribution of the studied sample of secondary school pupils in the city X during the year 2004 according to

consumption of high caloric diet & obesity.

Consumption of high

caloric diet

With obesit

y

Without

obesity

Total

Yes206080No16304320

Total36364400

Prevalence of obesity among those consumed high caloric diet (P1 ) =

20 X 100 = 25%80

Prevalence of obesity among those don’t consume high caloric diet (P2) =

16 X 100 = 5%320

The prevalence rate =

The total number of all cases (old and new) in certain area at a given time X 100 The total number of population in the same area and time

The uses of cross-sectional study:

Estimation of prevalence rate of disease or any health related phenomena. It leads to formulation of hypothesis. It is suitable for chronic diseases with long latency. Quick & cheap, compared to prospective cohort study.

The Limitations of the cross-sectional study: Can’t be used to test hypothesis (chicken egg dilemma). Deals with survivals only but those who died, cured or migrated are not included. Can’t be used in acute diseases of short duration. Not suitable for rare diseases (Compared with the case control study)

Analytical epidemiology (Finding the cause-effect)

Try to identify causal relationships between some risk factors & occurrence of disease.

Try to answer why the disease occurs.

ANALYTICAL STUDIESIt is formed of 2 comparative groups.

Their types are: 1- Case-control 2- Cohort: -Prospective -Retrospective 3- Comparative cross-sectional

Retrospective )Case-Control(

a b

dc

DISEASEPresent AbsentEXPOSURE

Present

Absent

Cases

Controls

Total

Total

Pros

pect

ive

)

Coh

ort

(

Exposed

Not exposed

A fourfold table

Mausner, 1985

Design of a Case-Control Study

Case Control Studies

The features of case control Study

The subjects are selected on the basis of whether they have: - The condition (e.g. cases with disease or any health related events) or - Free from the condition (the control). Both are then compared with respect to the having the history of exposure or certain characteristic. It is used to test the hypothesis i.e. the causal association between the exposure and the events (disease).

Steps to conduct the case control study:1-Selection of cases:a. Establishment of diagnostic criteria (standard case def.). b. Sources of cases: i) Hospitals or any health care facility ii) General population: 2-Selection of the control: a. Matching.b. Sources of the control. i) Hospitals ii) Relatives. iii) Neighborhoods. c. Size of the control 3. Assessment of the exposure:4. Analysis and interpretation of the results. a. Tabulation of data b. Flow chart c. Calculation & interpretation of the estimated risk (odds

ratio)

2-Selection of the control: a. Matching: It is the process in which we select the control

in a way that they have the same confounding factors affecting the cases (e.g. age) which are known to influence the outcome of the disease.

b. Sources of the control:. i) Hospitals or any health care facilities. ii) Relatives: They are co-operative however they are unsuitable

control when genetic conditions are under study. iii) Neighborhoods vi) General population: it is expensive, time consuming, difficult

and the individuals may be uncooperative. c. Size of the control: If the number of the cases is >50 cases ,use one control for each case. If the number of cases is < 50, use 2,3 or even 4 controls.

3. Assessment of the exposure: By interview, by questionnaires, or by studying past records of cases “hospital records, school or occupational records”

4. Analysis & interpretation of the results:Tabulation of data:

Framework of case control StudyExposureCasesControlExposedab

Not ExposedcdTotala+cb+d

The rate of exposure among the cases = The number of those exposed among the cases X100 = a x 100 The total number of cases a + c

The rate of exposure among the controls = The number of those exposed among the control X100 = b x 100 The total number of control b + d

ExposureCasesControlExposedab

Not ExposedcdTotala+cb+d

b. Exposure rate:

c. Estimation of risk associated with exposure: (Odds Ratio)

Measure of the strength of the association between the risk factor & the disease.

How to calculate the odds ratio? What is the odds that a case is being exposed? a ÷ c = a a +c a+c c

What is the odds that a control is being exposed? b ÷ d = b b+d b+d d

What is the estimated risk (odds ratio)? a ÷ b = a d c d b c

The odds ratio = ad bc

ExposureCasesControlExposedab

Not ExposedcdTotala+cb+d

1No relation

between exposure

& disease

RiskProtective

Benefits of case control study:

1- Suitable :to test the hypothesis that the disease of interest is caused by an exposure.for diseases with long latency period. to study rare diseases 2- Easy, rapid, & cheap (compared withy prospective cohort)3- Requires few subjects.4-Can examine multiple exposure factors for a single disease.5-Estimation of the risk (odds Ratio)6-Minimal ethical problems.7- No attrition problem.

Limitations of case control study:

1- Incidence & Prevalence rates can not be calculated.

2- Not suitable for studying rare exposures.

3-The problem of bias.

What is Bias?

Bias is any systematic error in the determination of

the association between the exposure and the disease.

Types of Bias:•Recall bias.•Bias due confounding factors. •Selection bias.

Selection bias: The cases may not represent those in the general population. Example: The health awareness about the association between CHD and smoking influences the selection of cases. Smokers at the time of onset of CHD are more likely to attend the health care facilities than those with similar symptoms who are non smokers. This results in an artificially high proportion of cases of CHD among smokers.

Confounding factors:Factors other than the studied one that disturb relation between the studied exposure & disease of interest.

For example: Association between average family size & frequency of iron deficiency anemia may be due to other factors such as pattern of diet, infectious diseases, socioeconomic conditions and parasitic infections.

The Impacts of the Confounding Factors

Large Family size (Exposure)

Iron deficiency anemia (condition)

Parasitic InfectionPattern of Diet

Mothers AwarenessMothers Education

(Confounding factors)

Recall (Interview) ProblemsLimitations in recallRecall bias

One group (e.g., mothers with child with birth defect) may clearly remember (recall) an event (e.g., mild respiratory infection)

Other group (e.g., mothers with healthy child) may not recall any such event

Matching

Concern that cases & controls may differ in characteristics or exposures other than that observed in the study

To overcome this problem, we can match cases in controls in regard to potential factors of concern

Matching selects controls that are similar to cases in characteristics such as age, race sex, socioeconomic status, occupation, etc.

MatchingGroup matching (frequency matching)

proportion of controls with a given characteristic (variable) is identical to proportion of cases with the same characteristic

Individual matching (matched pairs)for each case, a control is selected who is

similar to the case for a given variable(s)

Advantages 1-Inexpensive & not time

consuming.2-Suitable for rare diseases.3-Suitable for diseases with

long latent periods. 4-Can examine multiple

etiologic factors for a single disease at same time.

5- No Drop-out problem.

Disadvantages1-Relatioship between

exposure & disease difficult to establish

2-Inefficient for rare exposure.

3-Cannot calculate incidence.4-Selective & recall bias.

The Case Control Study

Example: An investigator selected 200 patients with basal cell carcinoma (BCC) admitted to X hospital during the year 2004, and 200 subjects free from the disease as a control from general population. Both groups were interviewed to obtain information on history of exposure to sunrays Those with history of exposure were 120 among cases and 40 among the control .

1-Draw the flow chart

2-Tabulate the data.

3- Mention the dependent, independent & the confounding factors.

4-Estimate the risk of exposure to sunrays.

History of sun exposure (n=120)

History of no sun exposure (n=80)

History of sun exposure (n=40)

History of no sun exposure (n=160)

Past Present

The direction of the study

Patients with BCCn=200

Control free from BCCn=200

The Flow Chart

The Independent variable : The Exposure to Sun Rays .

The Dependent variable : The BCC

The Confounding factors : Sex, Age, Local Chemicals, Cosmetics or Chronic dermatitis, Occupation .

Distribution of patients with BCC admitted to X hospital & their controls during 2004 according to history of

exposure to sunrays.History of exposure to sunraysBCC CasesControl

Yes12040No80160

Total200200

Estimation of the risk:Rate of exposure to sun rays among the cases= 120X100 = 60% 200Rate of exposure to sun rays among control= 40X100 = 20% 200

Because 60% > 20 % So there is an association between BCC and exposure to sun rays

History of exposure to sunrays

Patients with BCC

The control

Yes)a( 12040 )b(No)c( 80160 )d(

Total200200

Calculation & interpretation of Odds ratio:

Odds Ratio = 120X160 = 6 40X80

Interpretation of the Odds ratio:

Those exposed to sun rays are 6 times at risk to have BCC than those not exposed.

ORPatients with BCC tended to be exposed to sun rays 6 times

greater than those without BCC.

ORIt is 6 times more likely to find prior exposure to sun rays

among patients with BCC than among those free from BCC.

Cohort studies

Another type of analytical study which is usually done to obtain evidence to support the existence of an association between suspected cause and a disease

Cohort study has 2 types:Prospective cohort study: All data will be collected in

the future

Retrospective prospective study: where part is carried out retrospectively by collecting existing data then the cohort is followed till the outcome under study is developed.

Concept of a cohort

In epidemiology the word cohort is defined as a group of people who share a common characteristic or experience within a defined period of time (e.g. age, occupation, exposure to drug, vaccine, pregnancy, birth or marriage cohorts).The comparison group may be the general population from which the cohort is drawn or may be another cohort of persons thought to have had little or no exposure to the substance in question.

Known by a variety of names

Prospective study

Longitudinal study

Incidence study

CauseRF

exposure

Effect)Disease(

Cohort

Case control

Cohort Studies

Retrospective )Case-Control(

a b

dc

DISEASEPresent AbsentEXPOSURE

Present

Absent

Cases

Controls

Total

Total

Pros

pect

ive

)

Coh

ort

(

Exposed

Not exposed

A fourfold table

Mausner, 1985

Prospective cohort

The features of prospective cohort of the study:

A group of individuals are defined on the basis of the presence

or absence of exposure to a suspected factor for a disease.

At the time when the exposure status is defined, all individuals

must be free from the disease under investigation.

They will be followed over a period of time to assess the

occurrence of that outcome.

Steps to carry out the prospective cohort study:

1- Selection of the cohorts: This depends on exposure:

2-Obtaining data on exposure: a. Interviews or questionnaires from cohort members b. Review of medical records: e.g., dose of radiation, kinds of surgery, details of vaccination or medical treatment. c. Medical examination or special test: blood pressure, cholesterol d. Environmental survey: e.g. the level of air pollutants.4-Follow up.5-Analysis & interpretation.

ExposureCohortPattern of Pop.The comparison

Common (Smoking)

General population)smokers &non smokers(

HeterogeneousInternal

Rare (Radiation)

Special group (Radiologists)HomogenousExternal

Elements of a cohort study

1- Selection of the study subjects:General population (when exposure or the cause of the disease is fairly frequent in the population. The cohort residing in the same geographical area as in (Framingham study)Selected groups as professional groupExposure group: cohorts selected with special exposure to physical, chemical or other disease agents.

2- Obtaining data on exposure from: Cohort members, questionnaire through personal interviews, or mailed questionnaire in large cohorts.Review of records: dose of radiation, number of surgeries, details of medical treatment,Medical examination or special tests e.g. BP measurement, serum cholesterol……. etc.

3- Selection of comparison group:Internal comparison: the same cohort that enters the study may be classified into several comparison groups according to the degree of exposure (smoking, cholesterol) before the development of the disease in question.External comparison: if all of my cohort is exposed to the risk factor (radiologist, so we compare with ophthalmologist, this would make external comparison).

Comparison with the rates of the general population e.g. mortality experience of the exposed group is compared with mortality experience in the general population (comparing the mortality rate of asbestos workers with the mortality rate in the general population).

4- Follow up:

- Periodic medical examination- Reviewing physicians and hospital records- Routine surveillance of death records -Mailed questionnaires-Telephone calls-Home visits.

5- Analysis of cohort study:

The data obtained are analyzed in terms of: A- Incidence rates of outcomes among exposed and non exposed groups.B- Estimation of RISK.

Benefits of cohort study:

-It is of value when the exposure is rare.-Can examine multiple effects of single exposure .-It estimates : Incidence of disease among exposed & non exposed.Relative & attributable risk.Dose response relationship .-It allows testing the hypothesis.- No selection bias since the exposure is assessed prior to the occurrence of the disease, the outcomes could not influence the selection of the exposure.

III) The limitations of the prospective cohort study:

Not suitable for studying rare diseases. Loss of experienced staff, loss of funds. Change in the environmental factors.

Change in standard diagnostic methods or diagnostic criteria of diseases.

The study itself may alter the participants behavior. Attrition problem:Drop-outs.

Ethical problems.Expensive.

Time consuming (20-30 years in cancer studies).

Cohort studiesAdvantages

1-Time sequence of Relationship between exposure & disease can be established

2-Suitable for rare exposures.

3-Can calculate incidence.

4-Selective & Recall bias are absent.

Disadvantages 1-Expensive & time

consuming2-Not feasible for rare

diseases3-Drop-outs.

Example: A group of individuals are classified according to exposure to sunrays into exposed (n= 400) and not exposed (n= 400). The two groups are similar in all other aspects as age, sex, and social class. They are followed up for ten-year period. Among those exposed, 40 BCCs are detected and among those not exposed, 4 cases of BCC were detected.

1-Mention the type of the epidemiologic study.

2- Draw the flow the flow chart

3- Tabulate the data.

4- Calculate the risk of exposure to sunrays.

Persons developed BCC (n= 40)

Persons didn’t develop BCC (n= 360)

Persons developed BCC (n=4)

Persons don't develop BCC (n=396)

Persons exposed to Sunrays

n=400

Persons not exposed to Sunrays

n=400

Present Future Direction of the study

The flow Chart:

Tabulation of data:

Distribution of the cohort groups (exposed & not exposed to sun rays) according to the detected BCC after a 10 years

follow up period.

Exposure to sunrays

Persons with

BCC

Persons without BCCTotal

Yes )Ee(40360400

No)E0(4396400

Calculation of the rate of occurrence of BCC:

The incidence of BCC among exposed = 40 X100 = 10% (Ie) 400

The incidence of BCC among not exposed = 4 X100 = 1% (I0) 400

Calculation of Risk:

1- Relative Risk (RR).

2-Attributable risk percent (ARP).

Estimation of risks:

1- The relative risk: (Risk Ratio) (RR)

It is the ratio of the incidence among exposed to that of none

exposed.

RR = Incidence among exposed = (Ie) = 10 = 10 Incidence among none-exposed (I0) 1

Measure of the strength of association between the suspected cause & the effects based on prospective studies (cohort studies).

1No relation

between exposure

& disease

RiskProtective

In the previous example:

RR=10 indicates that those exposed to sunrays

are 10 times at greater risk to develop BCC

than those not exposed to sunrays.

Amount of disease that can be attributed to a certain exposure.

2- Attributable risk percent (ARP):

ARP = ( Ie - I0 )X100 (Ie)

ARP in previous example= (10 -1)X100 = 90% 10

This indicates that 90% of the BCC is attributed to exposure to sunrays i.e. 90 % of BCC could be prevented if persons avoid exposure to sunrays.

Rates in cohort study

Cigarette smoking+ve lung cancer

-velung cancer

Total

Yes7069307000

No329973000

Incidence rate of lung cancer among exposed (smokers) = 70/7000 = 10 per thousand

Incidence rate of lung cancer among non exposed (non smokers) = 3/3000 = 1 per thousand

Estimation of risk

Relative Risk (Risk ratio): Ratio of the incidence of the disease among exposed to the incidence of disease among non exposed

RR = IR among exposed/ IR among non exposed = 10/1 =10

RR for development of lung cancer = 10

This indicates that the risk of developing lung cancer is 10 times higher in exposed compared to non exposed group.

Cohort Study (Prospective Design)

Passive smoking & respiratory infections in children

Is passive exposure to tobacco smoke associated with increased respiratory infections in children ?

Design:Children exposed and not exposed tobacco smoke

in their homes Follow them in time for disease occurrence.

Children >)12 yrs(

1000

Family smoker500

childrenExposed

Family non-smoker

500 childrenNot exposed

1 year

Diseased 300

Not diseased 200

Diseased 120

Not diseased 380

OutcomeStart

Rate: Incidence rate

•Incidence of Resp. Infection among exposed children: 300

500 = 60%

•Incidence of Resp. Infect. Among non exposed children: 120

500 = 24%

Cohort Study (cont.)Relative Risk: Incidence rate among exposed Risk Ratio Incidence rate in non exposed.

60 24 = 2.5

Relative Risk is a direct measure of risk (to assess the etiologic role of a factor in disease occurrence).

300 x 500 500 120

Cohort Study (cont.)

Relative Risk:

Smoking- Lung Cancer mortality: RR=18.57- Myocardial infarction mortality: RR=1.35

It measures the strength of association

Examples from the literatureFramingham Heart Study initiated in 1948 by US Public Health Services: to study the

relationship of a variety of factors to the subsequent development of heart disease

Group of persons30 – 62yrs

6,500Both sexes

20 years follow up

Information:S. cholest.levelBl.pressure , weightCig. Smoking

outcome

Occupation Based Studies to study effect of exposures

•Benzene workers & Leukemia• Coke-oven workers & lung cancer

•Asbestos workers & lung cancer•Radium dial painters & oral cancer

OBJECTIVE: To identify risk factors for breast cancer among female survivors of childhood cancer.

Exposure: Survivors of childhood cancer are at risk for secondary breast cancer.

DESIGN: Retrospective cohort study.

SETTING: The Childhood Cancer Survivor Study (CCSS), a multicenter study of persons who survived more than 5 years after childhood cancer diagnosed from 1970 to 1986.

PARTICIPANTS: Among 6068 women in the CCSS, 95 women had 111 confirmed cases of breast cancer.

MEASUREMENTS: Standardized incidence ratios for breast cancer were calculated by using age-specific incidence rates in the general population. Breast cancer incidence was evaluated with respect to primary cancer diagnosis and therapy, age at and time since primary diagnosis, menstrual and reproductive history, and family history of cancer.

RESULTS:

Breast cancer risk was increased in survivors who were treated with chest radiation therapy (standardized incidence ratio, 24.7 [95% CI, 19.3 to 31.0]) and survivors of bone and soft-tissue sarcoma who were not treated with chest radiation therapy (standardized incidence ratios, 6.7 and 7.6, respectively).

Survivors of childhood sarcomas and those who received chest radiation therapy are at risk for secondary breast cancer. When assessing a survivor's risk, clinicians should consider primary diagnosis, previous radiation therapy, family cancer history, and history of thyroid disease.

Case-control or Cohort.How to choose?

When the outcome is rare start with it. So case-control study. Search for possible incriminated exposures

retrospectivelyWhen the exposure is rare start with it. So cohort study. Follow them up compared with those unexposed When the exposure is new follow it up.

Socohort

Cancer lung &SmokingCase-control Cohort - One group already have

ca.lung “cases”- 2nd healthy group “controls”- Comparing smoking status

“smoker or not & duration of smoking in past history of both groups”

- Start by a cohort selected from population living in a locality.

- Individuals in this cohort divided into exposed “smoker” & non-exposed “non-smoker”

- Then these 2 groups followed for some period of time to find out who among both groups will develop ca.lung.

B. Experimental (Intervention) studies: (Proving cause-effect relationship)

Active trial to change disease determinant by the investigator who allocates the exposure & follows the subjects.

Can be viewed as a type of prospective cohort study.

Ethical points must be considered:

it should have beneficial effect to patients, not to harm anyone by intervention

participants should know what the experiment is and have the right to refuse

if any unplanned complications occur to any participant he should be excluded from the trial and treated.

Types of experimental studies:

a) Clinical trials: It is usually used to assess efficacy of a new line of ttt (a

new drug for example) or to compare 2 types of ttts: surgical or medical.

Diseased subjects are randomly allocated into 2 groups, "ttt” group (who are given the new drug) and "control group" (who are given the usual ttt or no ttt in placebo).

Results are assessed by comparing health improvement of the 2 groups at end of trial.

Example: surgical or medical treatment of peptic ulcer

EXPERIMENTAL STUDY

Random Allocation ?

Yes No

Randomized Non-Randomized

Controlled trial Controlled trial (RCT)

Randomization: assigned to ttt & control group.Matching: matched pair design to arrange ttt &

control groups similar for the main variables such as age, sex. Matching determine data analysis.

Cross–over design: In a clinical trial of short term benefits it may be appropriate to use participants as their self-controls.

Single & double–blind designs: single blind when the participants don’t know the preparation while in double blind method, both investigator & participants do not know, only (designer) knows. “Triple blind: subjects & investigators & statisticians”

b) Community trials: Involve people who are not diseased (but presumed likely

to be at risk) and the sample is drawn from the community. Data collection takes place in the field. For example: in studies carried out to assess the efficacy

of new vaccines. The participants are divided into 2 groups: one who is the experimental group (will take the new vaccine) and the 2nd is the control group (will not take the vaccine).

The participant will be followed to compare the level of occurrence of the disease in both groups. Therefore, these groups should be alike as much as possible in all aspects other than ttt /intervention received.

Hierarchy of major study designs

Systematic review of RCTs

RCT

Cohort

Case control

Cross sectional

Interventional

Observational

Validity

Exercise1:-Description of 35 patients with thyroid cancer

are regarding past history of exposure to radiation and response to surgical treatment

Feedback:-

Case series

Exercise2:-Patients admitted for uterine prolapse were age

and social class-matched with fellow patients without prolapse and surveyed as to chronic constipation history to assess the possible association of chronic constipation and uterine prolapse.

Feedback 2:-

Case-control study

Exercise3:-A 39-year old man who presents with mild sore

throat, fever, malaise and headache was treated with penicillin for presumed streptococcal infection.

He returned after a week with hypotension, fever and abdominal pain .

A diagnosis of Rocky Mountain spotted fever was made and he responded good to chloramphenicol.

Feedback 3:-Case report

Exercise4:-A total of 298 who have minor operations during

March 1980 in one hospital, half of them are known and recorded to be exposed to hepatitis B contaminated vials discovered and half of them to vials free of this pollution are followed up starting from July 2000 till 2010 to diagnose liver cancer.

Feedback 4:-

Retrospective cohort

Exercise 5:- 500 patients were classified according to their body mass index (obese

or not) and simultaneously according to having knee osteoarthrosis

Feedback of Exercise5:-

Cross sectional study

Exercise 6:-47 men between 40 and 64years of age who had major ECG abnormalities at initial examination and 144 men of the same age group with no ECG abnormalities were followed up for 20 years and deaths from CHD were recorded.

Feedback of Exercise 6:-

Prospective cohort study

Exercise 7:-An oncologist determined that 75 out of 100 randomly

selected leukemia patients had experienced exposure to ionizing radiation while 60 out of 100 randomly selected healthy individuals who did not differ from patient with respect to age or sex had experienced exposure to ionizing radiation .

Feedback of Exercise7:-

Case-control study

Exercise 8:-In one of two capital cities of two adjacent

governorates, health education & strict application of helmets use for motorcycle drivers were done & in the other city no application of such awareness or law & then the incidence of head injury among motorcycle drivers was found for a year

Feedback 8:-

Community trial

Exercise 9:-A team of clinical researchers decide to investigate if

ovarian cancer responds better to Taxol than to conventional chemotherapy. They choose suitable patients & randomize to Taxol & control groups (subjects are alike, apart from the exposure to which therapy).

The researchers measure % of tumors responding in both groups blindly.

Feedback of Exercise 9:-In this study we started with patients and

randomize to study & control group to test an exposure (therapeutic modality) which is assigned by researchers.

Hence, this is a Randomized controlled trial (RCT) (an experimental= interventional study)

Exercise 10:-Framingham study is a large scale study that was

initiated in 1949 to investigate putative risk factors for coronary heart disease (CHD). Study participants underwent a complete physical examination at beginning of study & every 2 years thereafter

What is the type of this study? Feedback of Exercise 10:-

Prospective cohort study