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Exercise on Study Design

Prof Md Anisur Rahman (Anjum)Prof & Head of the department Ophthalmology. Dhaka Medical

College. Dhaka

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Exercise: 1 A researcher with a medium-sized grant wants to study the

relationship between exposure to in-home treated drinking

water (such as Brita filters) and diarrhea among children in

three neighboring towns, in comparison to tap water. All three

towns use the same water source and treatment facility.

Which study design should the researcher choose and how

might she study this relationship?

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Answer of Exercise: 1.Cohort study. The researcher may randomly select 250

households with children to study and then determine

exposure status (whether the family uses regular tap water or

an in-home treatment). The researcher would analyze daily

logs of each household to gather data on cases of the

outcome (diarrhea) among the children and then compare

the number and frequency of diarrhea cases in the exposure

(home-treated water) and the control (tap water) groups.

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Exercise: 2. A researcher wants to survey the prevalence of STIs among

female college students at four universities. Two of these

universities have large educational and outreach campaigns

for sexual protection and testing, while the other two do not.

The researcher has very limited time and funds.

Which study design should the researcher choose and how

might she study this relationship?

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Answer of Exercise: 2.  Cross-sectional . For the cross-sectional study, researchers can

survey all or a sample of female students about their STI

status; for the ecological study, campus health records over

the last year can provide data on female students diagnosed

with STIs.

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Exercise: 3 A researcher wants to study whether women who breastfeed

have lower rates of breast cancer in later life. Funders would

like an analysis within one to two years.

Which study design should the researcher choose and how

might she study this relationship?

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Answer of Exercise: 3.• Case-control study. The researcher would enroll women with

the outcome (women with breast cancer who have had

children) to be cases and then match four times as many

women as controls (women without breast cancer who have

had children and are similar in age, SES, and health care

access as the cases).

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Answer of Exercise: 3• They would then interview all the women about their nursing

histories and record data on whether and how long the

women breastfed. The researchers can also collect data on

other factors that may affect the outcome. From this data,

they can examine whether women with breast cancer had

significantly less utilization of (in other words, exposure to)

breastfeeding than similar women who did not develop breast

cancer.

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Exercise: 4 A 39-year old woman presents with a mild sore throat, fever,

malaise and headache and is treated with penicillin, for

presumed streptococcal infection. She returns in a week with

hypertension, fever, rash and abdominal pain. She responds

favorably to chloramphenicol, after a diagnosis of Rocky

Mountain spotted fever is made.

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Answer of Exercise: 4 This is a case report. It is not usually regarded as an

"epidemiologic" study, since there is neither "population" nor

comparison group. Presentation of an interesting case can

serve to alert other health care professionals of the possibility

of misdiagnosing a potentially fatal disease.

• http://www.epidemiolog.net/epid168/labs/AnalyticStudExerI

nstGuid2000.pdf

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Exercise: 5• Cryptosporidiosis is an enteric illness that is frequently

waterborne. Khalakdina and colleagues (2003) could find no

published study of the risk factors for cryptosporidiosis in

immunocompetent adults. Patients with cryptosporidiosis

were recruited from a surveillance system, and age-matched

controls were recruited by random-digit dialing. Subjects in

both groups were interviewed by telephone to obtain

information about previous disease.

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Answer of Exercise: 5 At first glance this study might appear to be cross-sectional

because a telephone interview was used. However, the data

collected pertained to disease that occurred after exposure of

the cryptosporodiasis (for the case). Therefore, this study is

best described as case-control.

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Exercise: 6Brown and coworkers (2003) designed a study to determine the

efficacy of immunotherapy with ant venom for treating ant

stings. The study involved a group of adults who were allergic

to ant stings; each subject was randomly assigned to receive

either venom immunotherapy or a placebo. After a sting

challenge in which any reactions were recorded, the group

originally on the placebo was given the venom

immunotherapy, and after a sufficient time, they too were

given a sting challenge.

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Answer of Exercise: 6• This is not a classic crossover clinical trial because patients

who received the therapy were not subsequently given a

placebo. Why would a modified crossover study be necessary

in this study?

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The study design is interesting, and some might be tempted to

call it case-control. The purpose was to compare self-reported

therapy with actual therapy. Both of these measures (self-

reported and actual) occurred at the same time, so the study

also has some characteristics of a cross-sectional study. Our

opinion is that the study is case-control, but it illustrates the

difficulty in classifying studies cleanly into any scheme.

Answer of Exercise: 6

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1) Following are the characteristic of case control study:

a) Case-control study is usually retrospective.

b) Useful for hypothesis generation

c) Can only look at one outcome

d) Bias is a major problem

e) We measure relative risk in case control study

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a b c d eT T T T F

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2) Following are the characteristic of Cohort studies a) Cohort studies describe incidence or natural history.b) Retrospective cohorts where available are cheaper and

quicker.c) Confounding variables are the major problem in analysing

cohort studies.d) Subject selection and loss to follow is more in case control

study than cohort studye) Cohorts are heterogeneous people

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a b c d eT T T F F

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3) ________Is the classical form of research

a) Case control study

b) Cohort study

c) Experimental study

d) Cross-sectional study

e) Longitudinal study

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a b c d eF F T F F

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4) Which of the following is/are advantage of Case Control Studies?

a) They can simultaneously look at multiple risk factorsb) They are useful to initially establish an association between a

risk factor and a disease or outcomec) They take less time to complete because the condition or

disease has already occurredd) Unable to estimate incidence rates of diseasee) a, b, and c

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a b c d e

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6) In a case-control study to investigate oral contraception and breast cancer:

a) Cases would be women with breast cancer.b) Controls would be given oral contraception.c) Cases would be given oral contraception.d) Women with breast cancer would be randomly allocated to be

cases or controls.e) Controls would be observed for several years to see how

many developed breast cancer.

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a b c d eT F F F F

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7) In a case-control study, patients with lung cancer had a highly significantly lower cholesterol level than did controls. This provides strong evidence that:

a) Low cholesterol causes lung cancer.b) Here is evidence for a relationship between low cholesterol

and lung cancer in the sampled population.c) Low cholesterol is not related to lung cancer.d) Low cholesterol and lung cancer always go together.e) Low cholesterol is a risk factor for the development of lung

cancer.

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a b c d eF T F F F

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8) In a well designed clinical trial of treatment of ovarian cancer, remission rate at one year is similar for a new drug and usual care, The P-value is 0.4. This means that

a) Both treatments are effectiveb) Neither treatment is effectivec) The statistical power of this study is 60%d) The best estimate of treatment effect is 0,4e) It is not possible to decide on whether one treatment is better

than the other using this information alone

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a b c d EF F F F T

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9) Which of the following would occur in a longitudinal study?

a) Measures are taken from different participants over an extended period of time.

b) Participation is expected to last for a minimum of 24 hours.

c) Measures are taken from the same participants on different occasions usually over extended periods of time.

d) Measures are taken from participants in at least six different countries.

e) Measures more than twice

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a b c d eF F T F T

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10) The hallmark feature of an analytic epidemiologic study is: (Choose one best answer)

a) Use of an appropriate comparison groupb) Laboratory confirmation of the diagnosisc) Publication in a peer-reviewed journald) Statistical analysis using logistic regressione) Sample will be non randomly allocated

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a b c d eT F F F F