Sample Clicker Questions from Epidemiology Wayne Lamorte

Transcript Sample Clicker Questions from Epidemiology Wayne Lamorte

Identifying the Study Design

When reading a paper, it isn’t always clear what the study design is. Sometimes there is a combination of strategies. However, you should think about what the predominant design features are.

• Provides a framework for thinking about the study.

• Alerts you to weaknesses in some study designs.

Identifying the Study Design

Is it based on information about individuals?

Or averages in populations?

Correlational (Ecologic)

Identifying the Study Design

Is there just one group?

X X XXXXX X X

8 people with bird flu Did all subjects have the disease? (

Case Series

) Did they evaluate presence of disease and risk factors at the same point in time?

(

Cross-sectional Survey

)

Do you have heart disease?

Are you active?

Identifying the Study Design

• Two or more groups being compared?

How were they selected? Did they find people with disease [cases] and then find a comparison group without disease [controls]? (

Case-Control

)

XX X X X X X X

Compare past exposures • Identify non-diseased people & group them by risk factor status? Then follow them longitudinally to compare incidence? (

Cohort Study

)

X X X

Compare incidence over time

In prospective cohort studies conception, design, & enrollment occur before anyone develops the outcome.

Enroll non-diseased subjects; collect baseline exposure data Obese Lean Prospective Follow up at intervals to get accurate outcome data.

Compare incidence over time

X X X X Exposed Not Exposed Retrospective Identify a cohort retrospectively (e.g. tire manufacturing workers vs. desk employees. Look at what subsequently happened to them.

Compare incidence over time

X X X X

Identifying the Study Design

Did the investigators assign subjects to a treatment or intervention and follow them to compare outcomes?

(Clinical Trial)

Aspirin

Placebo Compare incidence over time

X X X

Oral Contraceptives & Liver Cancer

. Previous case reports of liver cancers in women on OCs. The authors contacted all cancer registries & collected information on all females with liver tumors.

OC Use Yes No Unknown 16 - 25 Age Category 26 - 35 % 31 % 43 20 49 10 48 1. Case series

What kind of study was this?

2. Case-control study

3. Retrospective cohort

4. Prospective cohort

5. Randomized clinical trial

36 - 45 % 22 29 49

State

Alabama Florida Georgia North Carolina Virginia Alaska Massachusetts New York New Jersey Rhode Island 1. Case series

Annual per capita Tobacco Sales

$600 $450 $500 $550 $400 $200 $150 $175

Lung Cancer Mortality Rate in 1965/100,000 pop.

92 75

What kind of study is this?

2. Case-control 3. Retrospective cohort 4. Cross-sectional survey 5. Correlational (ecologic) $250

0% 0% 0% 0% 0%

80 66 45 35 33 20 23 22

1830: Villerme notes that mortality varies among districts in Paris. He tried to correlate mortality with the distance of the arrondissement from the Seine River, the relationship of the streets to the prevailing winds, the arrondissement's source of water and local climatological factors such as soil type, exposure to the sun, elevation and inclination of the arrondissement.

Villerme found that mortality correlated closely with the degree of poverty in the arrondissement (estimated as the % of people exempted from tax). The findings did not spark action.

poorest wealthiest

Villerme found that mortality correlated closely with the degree of poverty in the arrondissement (estimated as the % of people exempted from tax). The findings did not spark action.

poorest wealthiest

What kind of study was this?

1. Case series 2. Case-control 3. Retrospective cohort 4. Cross-sectional survey 5. Correlational (ecologic)

20% 20% 20% 20% 20%

Lynn Lowell Springfield Newton Brookline Barnstable Median Household Income 38000 40000 30000 89000 68000 47000 Premature Deaths /100,000 470 466 459 218 233 275 500 450 400 350 300 250 200 150 100 50 0 0 20000 40000 60000 80000 100000

Investigators in Bergen, Norway sent questionnaires about respiratory health, allergies, smoking habits, and occupational respiratory exposures to a random sample of residents between the ages of 15-70. After two reminders, 2,819 responses were obtained. Of these, 1,646 reported exposure to tobacco smoke from other members of their immediate family.

What kind of study was this?

1. Case series 2. Case-control 3. Retrospective cohort 4. Cross-sectional survey 5. Correlational (ecologic)

0% 0% 0% 0% 0%

A study in N. Engl. J. Med. examined whether eating a Mediterranean diet had any association with mortality in Greek adults. A baseline questionnaire was used to determine how closely the subjects followed a traditional Mediterranean diet, and the group was followed for 2 years, during which they determined the cause of death among all subjects who died.

Mediterranean Diet Score High (close adherence) Medium Low (poor adherence) Deaths in 2 yrs

44 61 74

Alive

2586 3747 2383

Total

2,630 3,808 2,457

What kind of study was this?

1. Case-control 2. Retrospective cohort

3. Prospective cohort

4. Randomized clinical trial

Bacteremia, Fever, and Splenomegaly Caused by a Newly Recognized Bartonella Species. Eremeeva, et al.: N Engl J Med 2007;356:2381-7.

A 43-year-old American woman developed a fever after traveling in Peru for 3 weeks. She visited Lima and Nazca and then traveled to the Sacred Valley of Urubamba, followed by Cuzco and Machu Picchu, where she hiked. She received numerous insect bites. Sixteen days after returning to the US she developed fever, insomnia, muscle aches, nausea, headache, and mild cough. At the hospital she was found to have anemia and an enlarged spleen (splenomegaly). Laboratory tests determined that her blood was infected with a genus of bacterium called Bartonella.

What kind of study?

1. Case report 2. Case series

3. Case-control

4. Retrospective cohort 5. Clinical trial 6. Ecologic

0% 0% 0%

In 2003 a mass immunization against cholera was conducted in Beira, Mozambique. The following year there was an outbreak of El Tor Ogawa cholera in Beira. To assess the usefulness of the vaccine investigators compared the frequency of vaccination between persons with culture-confirmed cholera severe enough to have prompted them to seek treatment and age- and sex-matched neighborhood controls who did not have diarrhea.

1. Case series 2. Cross-sectional 3. Case-control study 4. Retrospective cohort 5. Prospective cohort 6. Clinical trial

Study type?

0% 0% 0% 0% 0% 0%

Risk of kidney failure associated with the use of acetaminophen, aspirin, and nonsteroidal antiinflammatory drugs. Perneger TV, et al.

People who take analgesic drugs frequently may be at increased risk of chronic kidney failure. These authors used a kidney dialysis registry to find 716 patients with kidney failure; they randomly selected 361 subjects without kidney disease from the same geographic area. They used phone interviews to estimate their cumulative past use of analgesics and compared the two groups.

What kind of study?

1. Case series 2. Case-control 3. Retrospective cohort 4. Prospective cohort 5. Clinical trial

0% 0% 0% 0% 0%

Adiposity as Compared with Physical Activity in Predicting Mortality among Women. Hu et al.: N Engl J Med 2004;351:2694-703. In 1976 the Nurse’s Health Study enrolled 121,700 female RNs who completed a mailed questionnaire regarding their medical history & lifestyle. The women have returned follow up information every two years. This study grouped them by exercise level & BMI and compared mortality rates among different levels of these two risk factors.

Type of study?

1. Cases series 2. Case-control 3. Retrospective cohort 4. Prospective cohort 5. Clinical trial

0% 0% 0% 0% 0%

Glucosamine, Chondroitin Sulfate, and the Two in Combination for Painful Knee Osteoarthritis.

Clegg, et al. N Engl J Med 2006;354:795-808.

Glucosamine and chondroitin sulfate are orally administered substances that have been used for years to treat joint problems in horses. Since they are relatively non-toxic there has been increasing interest in them for treating osteoarthritis, but there is controversy about their efficacy. These investigators randomly assigned 1583 patients with symptomatic knee osteoarthritis to receive 1500 mg of glucosamine daily, 1200 mg of chondroitin sulfate daily, both glucosamine and chondroitin sulfate, 200 mg of celecoxib daily, or placebo for 24 weeks. The primary outcome measure was a 20 percent decrease in knee pain from baseline to week 24. The primary outcome measure was whether the patient achieved a 20 percent decrease in pain as measured by the WOMAC pain subscale, a standardized, previously validity tool for assessing joint pain. What kind of study is this?

These investigators randomly assigned 1583 patients with symptomatic knee osteoarthritis to receive 1500 mg of glucosamine daily, 1200 mg of chondroitin sulfate daily, both glucosamine and chondroitin sulfate, 200 mg of celecoxib daily, or placebo for 24 weeks. They compared the groups with respect to decrease in knee pain from baseline to week 24 using the WOMAC pain subscale, a standardized, previously validity tool for assessing joint pain.

Type of study?

1. Case series 2. Case-control 3. Retrospective cohort 4. Prospective cohort 5. Clinical trial

0% 0% 0% 0% 0%

The frequency of new cases of tuberculosis in Boston during a given calendar year is…

1. Prevalence 2. Cumulative incidence 3. Incidence rate 4. None of the above

0% 0% 0% 0%

The % of deceased males who are found to have prostate cancer at autopsy?

1. Prevalence 2. Cumulative incidence 3. Incidence rate 4. None of the above

0% 0% 0% 0%

The % of people who have malaria that is resistant to treatment with chloroquine?

1. Prevalence 2. Cumulative incidence 3. Incidence rate 4. None of the above

0% 0% 0% 0%

The number of newly diagnosed brain tumors in a calendar year per 100,000 Massachusetts children?

1. Prevalence 2. Cumulative incidence 3. Incidence rate 4. None of the above

0% 0% 0% 0%

The number of previously healthy women who had a stroke during 40,000 person-years of follow up?

1. Prevalence 2. Cumulative incidence 3. Incidence rate 4. None of the above

0% 0% 0% 0%

In General:  Express prevalence and cumulative incidence as % or # per 1,000 or 10,000, etc.

 Express incidence rate as # per 1,000 person-yrs or 10,000 person-years, etc.

 Remember to state the time period of observation for cumulative incidence.

However, for the exercises that follow and for post class quiz #2, you will need to answer with the specific numerator and denominator for some questions, to make sure that you are including and excluding the right subjects.

Study population of

1,000

. Dashed line = disease present (Lung Cancer) Patients 1, 2, 3, & 4) had the disease before the study began.

During the year of the study, 6 new cases occur (start of dashed lines). Among the total of 10 cases , there were 6 deaths during the year The 990 other individuals in the study did not become ill or die.

1994 1995

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan 1<---------------------------------------------------------------------------------------------------------Alive 2<---------------------------------------

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead X Dead X Dead

Prevalence of disease on:

X Dead

Jan. 1, 1994?

July 1, 1994?

Dec. 31, 1994?

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Prevalence on Jan. 1, 1994?

A. 0/1000 B. 4/1000 C. 6/1000 D. 4/996 E. 5/996 F. 6/996

0% 0% 0% 0% 0% 0%

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Prevalence on July 1, 1994?

A. 4/997 B. 4/1000 C. 6/1000 D. 4/996 E. 5/996 F. 5/997

0% 0% 0% 0% 0% 0%

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Prevalence on Dec. 31, 1994?

A. 4/1000 B. 4/996 C. 4/994 D. 6/1000 E. 6/996 F. 6/994

0% 0% 0% 0% 0% 0%

Study population of

1,000

. Dashed line = disease present (Lung Cancer) Patients 1, 2, 3, & 4) had the disease before the study began.

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead X Dead X Dead X Dead

What was the cumulative incidence during 1994?

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Cumulative incidence in 1994?

A. 4/1000 B. 6/1000 C. 10/1000 D. 4/996 E. 6/996 F. 10/996

0% 0% 0% 0% 0%

Study population of

1,000

. Dashed line = disease present (Lung Cancer) Patients 1, 2, 3, & 4) had the disease before the study began.

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead X Dead X Dead X Dead

What was the population mortality rate during 1994?

(Use population at beginning of year for calculation)

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Population mortality rate in 1994?

A. 4/10 or 40% B. 6/10 or 60% C. 4/1000 or 0.4% D. 6/1000 or 0.6% E. 6/996 F. 10/1000

0% 0% 0% 0% 0%

Study population of

1,000

. Dashed line = disease present (Lung Cancer) Patients 1, 2, 3, & 4) had the disease before the study began.

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead X Dead X Dead X Dead

What was the case-fatality rate during 1994?

1994 1995

Dead

3<--------------------------------------------------------------

Dead

4<-----

Dead

5 -----------------------------------------------------------------------------------------------------Alive 6 ----------------------------

Dead

7 -------------------------------------------------------------------------Alive 8 ------------

Dead

9 ------------------------------------------------------------Alive 10 ---------------------------------------

Dead

Case fatality rate?

A. 6/10 or 60% B. 6/1000 or 6% C. 6/996 D. 4/996 E. 4/10

0% 0% 0% 0% 0%

A new disease occurs with constant IR= 3/1000 person-yr. Estimate the cumulative incidence over 5 years.

1. 0.03 over 5 yrs.

2. 0.010 over 5 yrs.

3. 0.015 over 5 yrs.

4. 0.030 over 5 yrs.

0% 0% 0% 0%

You should be able to calculate these measures of disease frequency and measures of association using a simple hand calculator.

Epi_Tools.XLS will also do them, but you need to be able to do them without Epi_Tools for the exams.

What does one measure and compare in a case-control study?

Cumulative incidence Incidence rate Risk of disease Risk difference

0% 0% 0% 0%

In a cohort study one may measure the degree of association between an exposure and an outcome by calculating either a relative risk or an odds ratio?

True False I’m not sure

0% 0% 0%

In a case-control study one may measure the degree of association between an exposure and an outcome by calculating either a relative risk or an odds ratio.

True False

0% 0%

When is an odds ratio a legitimate estimate of relative risk?

a case-control study.

When the exposure is relatively uncommon.

When the outcome is relatively uncommon.

When the sample size is large.