True/False (14 points) 1) _____Confounding is more likely to occur in observatio

ID: 3485916 • Letter: T

Question

True/False (14 points)

1) _____Confounding is more likely to occur in observational than in experimental epidemiology studies.

2) _____Bias is introduced primarily during the analysis stage of a study.

3) _____Factors that contribute to random error include poor precision, sampling error, and selection bias.

4) _____There is a potential of information bias in a clinical trial where the clinician who ascertains the outcome is aware of the treatment status of the participant being evaluated.

5) _____A confounding variable is a factor across which the association between the exposure and the outcome differ.

6) _____A cohort study was conducted to determine the association of physical activity and CHD in which the average age of the physically active group is 10 years younger than the average age of the inactive group. Age is a confounder given that the risk of CHD increases with age.

7) _____ Systematic errors can be reduced by: minimizing the random error in the study and vice versa.

Short Answer (14 points)

8) Consider each of the following scenarios and state whether the variable in question is a confounder:

A study of the relationship between contact lens use and the risk of eye ulcers. The crude relative risk is 3.0 and the age-adjusted relative risk is 1.5. Is age a confounder in this study? ?

A case-control study of the relationship between cigarette smoking and pancreatic cancer. In this study, coffee drinking is associated with smoking and is a risk factor for pancreatic cancer among both smokers and non-smokers. Is coffee drinking a confounder in this study? ?

A study of the relationship between exercise and heart attacks that is conducted among men who do not smoke. Is gender a confounder in this study?

A cohort study of the risk of liver cirrhosis among female alcoholics. Incidence rates of cirrhosis among alcoholic women are compared to those among non-alcoholic women. Non-alcoholics are individually matched to alcoholics on month and year of birth. Is age a confounder in this study? ?

9) A case-control study was conducted to determine if using any antihistamines around the time of conception increased the risk of birth defects in the offspring. No personal interviews were conducted regarding the subjects’ antihistamine use. Instead, women were considered exposed if computerized pharmacy records from their health maintenance organization indicated that they had filled at least one prescription for antihistamines within 500 days before the birth of the child.

Which type of observation bias is this data collection method most susceptible to? Also state whether it’s differential or non-differential? ?

Which type of observation bias is this data collection method least susceptible to in terms of exposure assessment? ?

10) State which method to control for confounding is being used in the following scenarios. In each scenario, exercise is the exposure, myocardial infarction is the disease, and gender is the confounder.

a.A study of exercise and myocardial infarction that includes men and women. Controls are selected so that the proportions of male and female subjects groups are identical. ?

b.A study of exercise and myocardial infarction that includes men and women. The study determines the relative risk separately for men and women and compares these to the crude relative risk. ?

11) The relationship between prevalence and incidence can be summed up by a mathematical formula. Write that mathematical formula here:

____________________________________________________________

Using the information you have provided above, complete the following sentences with one of the choices provided in parentheses:

If the incidence rate for a disease is low and the disease duration is short, we would expect the disease’s prevalence to be relatively __________ (high, low).

If the incidence rate for a disease is high and the disease duration is __________ (long, short), we would expect the disease’s prevalence to be relatively high.

The duration of disease A is longer than disease B. If the incidence of diseases A and B are the same, we can expect the prevalence of disease A to be relatively __________ (higher/lower) than disease B.

Please match the following descriptions with the type of measurement (count, attack rate, incidence density):

12) The number of cases of breast cancer that developed in a cohort of women from 1986 to 2012 per 100,000 person-years of follow-up

13) The number of people who died of liver cancer in 2009 in the United States

14) The percent of people who ate at a specific restaurant on June 15th, 2013 and contracted a salmonella infection

Calculations (22 points)

15) The baseline point prevalence of hypertension in African-American women aged 45-64 years included in the Atherosclerosis Risk in Communities (ARIC) surveillance study was found to be 53%. In this study, over a follow-up period of 7 years, the average yearly incidence of hypertension in African-American women was estimated to be about 5%, which was stable over the years. Using these data, estimate the average duration of hypertension in African American women in the ARIC study. (Hint: use the relationship between prevalence and incidence).

Explanation / Answer

ANSWER: 1). The given statement is FALSE since more confounding variables are likely to impact the results during experimental study designs.

2). The given statement is FALSE because bias is likely to occur at any given time during the study. Factors like social desirability may impact the results at various levels. The elements of subjectivity are likely to impact.

3). The given statement is TRUE since random error include all that given factors.

4). The given statement is TRUE since information bias refers to a type of cognitive bias, where there is a tendency to seek more information, when there is no actual need for it. In the given statement the clinician is already aware of the treatment status and has more information than required which could lead to an information bias.

5). The given statement is TRUE the confounder variable is a variable that affects the outcome, other than the intended act. it is something extra in the environment, that causes changes that weren't expected. The statement, therefore is true.

6). The given statement is TRUE confounding variables effects the intended outcome. Hence, here the age acts as a confounding variable. In other words, it (confounding)is also considered as third variable problem.

7) The given statement is FALSE Systematic errors, unlike random errors persist consistently throughout the experiment, and thus, just be reducing random error, cannot be tackled. Some ways in which the systematic error can be tackled are: reducing Zero-error, calibrations of the measuring instrument, etc.

Short answers:

Yes, age is the confounder in this study because, it impacts the ability to see.

A study of the relationship between exercise and heart attacks that is conducted among men who do not smoke. Gender is not a confounder in this study because the study conducted upon men only.

9). A case-control study was conducted to determine if using any antihistamines around the time of conception increased the risk of birth defects in the offspring. No personal interviews were conducted regarding the subjects’ antihistamine use. Instead, women were considered exposed if computerized pharmacy records from their health maintenance organization indicated that they had filled at least one prescription for antihistamines within 500 days before the birth of the child. The data collection method least susceptible to Nondifferential misclassification of the exposure.

10).

a. In this scenario differential classification method is used for confounding.

b. In this scenario also differential classification exposure method is used.

11). The relationship between prevalence, incidence can be summed up by the following formula.

Prevalence = incidence rate * average duration of disease

Mathematically,

P/(1-P) = IR * AVERAGE DURATION.

Here,

P is the population with disease,

(P-1) is the population without disease,

IR is the incident rate and finally average duration is the average time that have the disease.

Using the information, you have provided above, complete the following sentences with one of the choices provided in parentheses:

(a). If the incidence rate for a disease is low and the disease duration is short, we would expect the disease’s prevalence to be relatively low because, as per the formula mentioned above if IR is low and average duration is also short then multiplying two low components will give low prevalence.

(b). If the incidence rate for a disease is high and the disease duration is long as two long values multiplied will give a relatively high value.

(c). The duration of disease A is longer than disease B. If the incidence of diseases A and B are the same, we can expect the prevalence of disease A to be relatively higher as the IR is the same and the time for A is longer and after multiplication as per the formula the prevalence for A will be higher.

12). The number of cases of breast cancer that developed in a cohort of women from 1986 to 2012 per 100,000 person-years of follow-up. It will be incidence destiny.

13). The number of people who died of liver cancer in 2009 in the United States. It will be count.

14). The percent of people who ate at a specific restaurant on June 15th, 2013 and contracted a salmonella infection. It will be attack rate.

Calculations:

15).

Incidence rate- It is the proportion or rate of a newly diagnosed disease which is generally reported of new cases occurring in a year.

Prevalence rate-It is the rate or proportion of the actual number cases alive with disease during the period or a time.

Average Duration = (Prevalence) / (Incidence)

Prevalence rate for hypertension = 0.53 (given)

Incidence rate = 0.05 (given)

Average duration of hypertension in aferican-american woman =

(0.53)/0.05 = 10.6

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