3 Analytic Study

Epidemiological studies(practical)

Arrange the following study designs, from the weakest (top) to the strongest (bottom), according to their strength of evidence

in determining cause-effect relationship

Cohort studies - Randomized controlled trials - Case reports -Cross-sectional studies – Case series - Case control studies

1. Case report

2. Case series report

3. Cross-sectional study

4. Case-control

5. Cohort study

6. Randomized controlled trials

Increasing evidence of causality

MCQs: Select one answer.• Which of the following is TRUE about case-

control study :

1. Expensive.

2. Suitable for rare exposures.

3. Incidence rate can be calculated.

4. Can assess potential effect of several exposures.

MCQs: Select one answer.

• Which of the following is TRUE about cohort study:

1. Fast and inexpensive.

2. Attrition is one of the main disadvantages.

3. Prevalence rate can be calculated.

4. Start with case definition of the cases.


• Which of the following is TRUE about interventional studies:

1. Doesn't need a control group.

2. It runs retrospectively.

3. Inexpensive.

4. Allocate exposure randomly


• All of the following are descriptive studies EXCEPT:

1. Correlation studies

2. Case reports and case series

3. Case-control studies

4. Cross-sectional surveys


• Descriptive studies perform all of the following functions EXCEPT:

1. Measure the prevalence of a disease in the study population at one point of time

2. Describe the pattern of disease occurrence in relation to person, place and time

3. Generate hypothesis

4. Test hypothesis


• The sequence of events preceding the disease (temporal relationship between exposure and outcome) cannot be assumed to have occurred in:

1. Cross-sectional study

2. Prospective cohort study

3. Retrospective cohort study

4. Randomized controlled clinical trial


• In a cohort study, which of the following is INCORRECT?

1. Proceeds from outcome (disease) to exposure (cause/risk factor)

2. Starts with people exposed to risk factor or suspected cause

3. Incidence rates and relative risk can be calculated

4. Time consuming and expensive


• All of the following are advantages of case-control studies EXCEPT:

1. Cheap, easy and quick studies

2. Multiple exposures can be examined

3. Rare diseases and diseases with long latency can be studied

4. Accurate relative risk (risk ratio) estimation

5. Suitable when randomization is unethical


• In a study of the cause of lung cancer, patients who had the disease were matched with controls by age, sex, place of residence, and social class. The frequency of cigarette smoking was then compared in the two groups. What type of study was this?

1. Cohort (prospective)

2. Cross sectional

3. Case-control

4. Clinical trial

5. Correlation

MCQs: Select one answer.• A research team follows 2000 HBsAg positive

patients and a similar group of HBsAg negative at out patient clinics over 15 years to determine the rate of occurrence of hepatocellular carcinoma. This study is an example of a:

1. Cross sectional

2. Correlation (Ecological)

3. Prospective cohort

4. Case control

5. Not mentioned


• An investigator evaluated the association between the frequency of ischemic heart diseases and the average cholesterol level in different regions. This study is:

1. Cross sectional

2. Correlation (Ecological)

3. Prospective cohort

4. Case control

5. Intervention


• Cervical Pap smear was carried out for 1000 women above 40 years of age to sort out those with cancer cervix (D) from those without. They were asked about age of marriage (E). The epidemiological study design is:

1. Correlation

2. Case-control

3. Cross-sectional

4. Retrospective cohort

MCQs: Select one answer.• All of the following are steps necessary to

plan and conduct a case-control study EXCEPT:

1. developing and testing research instruments

2. defining the disease and exposure of interest

3. selecting cases and defining a control group

4. planning the analysis

5. determining the duration of the observational (study) period

MCQs: Select one answer.• In a double blind randomized controlled clinical

trial comparing the effects of a new (experimental) drug and a standard treatment, which of the following is TRUE?

1. Patient is not aware about the group allocation and treatment received

2. Neither the patient nor the doctor is aware about the group allocation and treatment received

3. The patient, doctor and investigator are unaware about the group allocation and treatment received

4. Each patient receives both treatments


• An investigator screened 1000 women above 50 years of age using mammography to sort out those with cancer breast from those without. He also asked about current use of oral contraceptive pills intake. This epidemiological study design is:

1. Correlation.

2. Case control.

3. Cross sectional.

4. Retrospective cohort.

During pre-placement examination of 200 new employees, 20 persons were hypertensive among 80 smokers, while 6 hypertensive persons were detected among the remaining 120 non-smokers.

What type of study is this?

A. Case-control study

B. Cross-sectional study

C. Prospective cohort study

D. Correlation study

Draw the flow chart of this study design.

Study population

Smokers

Hypertensive

Non Hypertensive

Non-smoker

Hypertensive

Non Hypertensive

Tabulate the data in a 2 X 2 table.


HTN Total

Yes No

Smokers

Non-smokers

Total

Tabulate the data in a 2 X 2 table.


HTN Total

Yes No

Smokers 20 60 80

Non-smokers

6 114 120

Total 26 174 200

What rate (s) can you calculate from this table?

• The prevalence of hypertension among the smokers

=(20/80) X 100 = 25%

• The prevalence of hypertension among non-smokers

= (6/120) X100 = 5%

HTN Total

Yes No

Smokers 20 60 80

Non-smokers

6 114 120

Total 26 174 200

What hypothesis can you formulate?

Null hypothesis: there is no relation between smoking and hypertension.

Alternative hypothesis: there is a relation between smoking and hypertension.

Can you calculate the risk of smoking?

Yes □ No □

because it’s a descriptive study, we can’t calculate incidence rate to calculate risk

• A research team wished to investigate a possible association between tobacco use and oral lesions among a group of workers. At periodic employment examination, each worker was asked about tobacco use, and a dentist examined them for the presence of oral lesions.

• What type of study is this?

1. case-control

2. cross-sectional study.

3. cohort study

4. clinical trial

5. none of the above

• The prevalence rate of tobacco use among the study workers is 110 /146 x100

( √ )

• The prevalence rate of oral lesions among workers who use tobacco is 82/146 x 100

( × )

Tobacco

use

Mouth

lesion

No lesion Total

User 80 30 110

Non-user 2 34 36

Total 82 64 146

The data on these workers (n= 146) were tabulated as follows:

• During the year 2007, 70 cases of lung cancer was diagnosed among 1000 adult males who are currently smokers. On the other hand, 10 new cases of lung cancer were diagnosed among 1000 adult males who are non smokers.

• Tabulate the data

Cancer lung

No cancer

total

smokers

Non-smokers

Total

During the year 2007, 70 cases of lung cancer was diagnosed among 1000 adult males who are currently smokers. On the other hand, 10 new cases of lung cancer were diagnosed among 1000 adult males who are non smokers.

Cancer lung

No cancer

total

smokers 70 930 1000

Non-smokers

10 990 1000

Total 80 1920 2000

• Calculate the incidence rate of lung cancer among smokers.

• 70/1000x1000=70 cases/1000 smokers

• Calculate the incidence rate of lung cancer among non-smokers

• 10/1000x1000=10 cases/1000 smokers

Cancer lung

No cancer

total

smokers 70 930 1000

Non-smokers

10 990 1000

Total 80 1920 2000


• 70/1000x1000=70 cases/1000 smokers


• 10/1000x1000=10 cases/1000 smokers

Calculate the relative risk:

• RR=incidence rate among exposed/incidence rate among non-exposed

• 70/10=7

Interpret the value of the relative risk:

Smokers are 7 times more at risk to develop cancer lung as compared to non smokers


• 70/1000x1000=70 cases/1000 smokers


• 10/1000x1000=10 cases/1000 smokers

Calculate the attributable risk percent:

• attributable risk =incidence among exposed –incidence among non-exposed/incidence among exposed X 100

• 70-10/70=• 86 %Interpret the value of the

attributable risk percent• This indicates that 86% of the

lung cancer among smokers is attributed to smoking i.e. 86 % of lung cancer among smokers could be prevented if smoking is eliminated.

• Write down the type of study that matches with each of the following statements: • Starts with persons with and without the disease

and determine exposure

Case control study

• Can study multiple exposure

Case control study

• Exposure and disease are assessed simultaneously

Cross- sectional study

• Useful for long latency diseases

case control study/ retrospective cohort

• Incidence rate can be measured

cohort study

Flow chart of different study designs

• Label these flow charts and mention the name of the study in each:

• Time

Present future

Name of the study: prospective cohort

Study population

Exposed

Out come +ve

Out come

–ve

Non- exposed

Out come -ve

Out come +ve

sample

cases

exposed

Non-exposed

control

exposed

Non-exposed

TimePast present

Name of the study: case-control study

Mention the name of the study for each of the following diagrams:

? +

? -

Name of the study:

case control study

investigator Disease Exposure


?

-

Name of the study:

prospective cohort study

Exposure investigator Disease


Name of the study:

Retrospective cohort study

Exposure investigator

Disease

?

-

Past Present

Interpretation of R.R or O.R:

• If = 1, denotes that:

No relation between characteristic and condition

• < 1, denotes that:

the characteristic is a preventive factor for the condition.

• > 1, denotes that:

The characteristic is a risk factor for the condition

Tick (√) or (X):

• Odds ratio can be calculated from case control studies

( √ )

• Recall bias is common in cohort study

( × )

• In cohort study, we classify study population according to exposure status

( √ )

• In cohort study, we follow exposed population with no need for a control group

( × )

• Both relative risk and attributable risk can be calculated from case-control study

( × )

• Randomization is not necessary in experimental studies such as clinical trials

( × )

• Case-control study is more expensive than cohort study

( × )

• Case definition of disease under study is first step in case-control study

(√ )

• Therapeutic and preventive studies are the main types of intervention studies

( √ )

A case-control study was conducted in El ShatbyHospital, Alexandria, to study the relationship between low birth weight and neonatal death.

Table: Relationship between low birth weight and neonatal death in a case-control study in El ShatbyHospital

Low birth weight Neonatal deaths Controls Total

yes 28(64%) 29 (12%) 57

No 16(36%) 208(88%) 224

Total 44(100%) 237(100%) 281

- Draw the flow chart of the study

sample

Cases of neonatal deaths

LBW

NO LBW

CONTROL

LBW

NO LBW

Estimate the risk and interpret it.

Odd’s ratio= axd/bxc=28x208/29x16=12.5

Deaths among neonates are 12.5 times more likely to occur among low births neonates as compared to normal weight neonates

• Put (true) or (false) opposite each of the following statements about prevalence of a disease:

• It measures all current cases (old and new) of the diseases in the community

( √ )

• It depends on incidence of the disease

( √ )

• It can be used to determine the health care needs of a community

( √ )

Select the appropriate study design to investigate the following: is

CASE CONTROL COHORT

- Rare disease

- Rare exposure

- Multiple outcomes

- Several risk factors

- Dose- response

relationship

- Disease with long latent

period

√

√

√

√

√

√

• Write down the name of the epidemiological study design that:

• Estimates incidence

(COHORT STUDY)

• Estimates prevalence

(CROSS-SECTIONAL STUDY)

• Compares the proportion of the exposed among diseased and non-disease

(CASE-CONTROL STUDY)

• Estimates odds ratio

(CASE-CONTROL STUDY)

• Exposure and diseases are evaluated at the same time

(CROSS-SECTIONAL STUDY)

• Uses a population, not an individual, as a unit of inquiry

(CORRELATION STUDY)

• Tests hypothesis and takes short time

(CASE-CONTROL)

• Needs long time of observation

(PROSPECTIVE COHORT) ×

State true or false:

a) An odds ratio of one means that the exposure has no association with the disease. ( )

b) The incidence rate can always be estimated from a case-control study. ( )

c) A relative risk less than one means that the factor under study is a preventive(protective) factor.( )

d) The prevalence rate measures the rate of development of the disease. ( )

e) The odds ratio is the only measure of association that can be measured from case-control studies. ( )THANK YOU

√

×

√

√

×

Thank You&

Good Luck

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3 Analytic Study