Quant midterm (1-6) multiple choice

fixed population

membership defined based on some event that happens once

• membership is permanent

dynamic population

membership is defined as being in a state or condition

• membership might be transient (short)

case series study

a detailed report on a single group with new or unusual health outcomes

• S: quick and inexpensive, recognizes new emerging health problems, hypotheses based on similarities

• W: no formal comparison group, temporal sequence unclear

cross sectional study

a study that compares current exposure status to current disease status at a single point in time

• measures PREVALENCE (snapshot of population)

• collected on each individual

• S: quick and inexpensive, useful for early stage knowledge

• W: temporal sequence unclear, long duration may bias results

ecologic study

a study that examines associations between exposures and outcomes on a population level

• S: quick and inexpensive, useful for early stage knowledge, wider range of exposures

• W: “ecologic fallacy”- for an exposure to cause an effect in an individual, the exposure and effect should occur in the same person, little to no control for confounding variables

dichotomous

two possible responses

• yes/no

• cancer/no cancer

• disease/no disease

ordinal

more than two ranked responses

• physical activity (<30, 30-180, >180)

• number of strokes (0, 1, 2, >3)

• overall health (poor, fair, good, excellent)

• hispanic/non hispanic

categorical

responses are grouped and unordered

• sex

• religion

• race

continuous (measurement)

assumes any numerical value between a minimum and a maximum

• systolic blood pressure in mmHg

• weight in pounds or kg

• height

acute exposures

occur for relatively short duration, short term contact with an agent or experience, may or may not repeat

• pesticide poisoning, spilling acid on hand, natural disasters, food poisoning

chronic exposures

over a long period of time, possibly over a lifetime

• outdoor air pollution in city where you live, ingestion of disinfection byproducts in drinking water, occupational, radon in your basement, neighborhood poverty

constituent exposures

part of an individuals biological makeup (intrinsic), unchanging and stable from birth acrosss the life course

• genetics, ancestry

time-varying exposures

vary across the life course of an individual

• diet, exercise, smoking, alcohol consumption, martial status, family status, UV exposures

critical window

specific period of increased susceptibility to health effects

induction time

period during which casual mechanisms that involve exposure become complete to produce disease

latent period

interval between disease causation related to exposure and detection/diagnosis of disease

exposome

measure of all the exposures of an individual in a lifetime and how those exposures relate to health

prevalence formula

= # existing cases at time point / # in total population at time point

cumulative incidence formula

= # new cases during time period / # in total population at risk during time period

incidence rate formula

= # new cases during time period / total person-time of observation in a population at risk

• person-time: amount of time each study participant is under observation

Type I error

reject the null when there is no association or different (false positive)

Type II error

fail to reject the null when there is an association or different (false negative)

H0 null hypothesis

hypothesis of no difference, no association, or no change

HA alternative hypothesis

hypothesis of difference, association, or change

reject the null hypothesis

strong evidence, statistically significant result (less than or equal to 0.05)

fail to reject null hypothesis

weak evidence, not statistically significant result (greater than or equal to 0.05)

victims of hurricane katrina would be best defined as which of the following types of populations

a fixed population defined by a life event

which of the following is the best example of a descriptive research question

does the occurrence of pediatric emergency room visits vary by season

which of the following is NOT an essential attribute of a cause

biologic plausibility

which of the following is the best definition of “latency period”

time interval between disease initiation and disease diagnosis

which of the following is a limitation of case reports and case series

no formal comparison group

which of the following types of exposures can be studies in an ecologic study

all of the above

which of the following statements about descriptive studies is true

ecologic studies compare the average exposure level and the overall frequency of a health outcome across populations

a group of researchers measures BMI among adults living in Australia and finds that BMI is skewed to the right. Which of the following is the best way to summarize the central tendency and variability of BMI in this population

median and IQR

measuring exposure levels of air pollutants in Boston using stationary air monitors does which of the following

provides a mean of estimating average exposure at a community level

which of the options below is an example of a microenvironment

a home or workplace

the movement of contaminants within or between environmental media (water, air, soil, and food) is an example of which of the following

transport

ingestion of a chemical contaminant is an example of which of the following

an exposure route

a “threshold dose” is which of the following

the lowest dose of a chemical contaminant that produces toxic effects

the threshold dose for carcinogens varies widely (T/F)

false

which of the following is an example of a critical window

zika virus infection in a pregnant person producing microcephaly in the newborn baby

induction is the length of time between exposure and disease initiation (T/F)

true

the internal concentration of a toxic substance that has been ingested, inhaled, or absorbed through the skin depends on which of the following

both amount ingested and body size (weight) of person

which of the following is an example of an acute exposure

burning ones hand with acid

the weymouth health survey was conducted in 2002. among 3,232 adult respondents, 288 (about 9%) reported that they had type 2 diabetes. which measure of disease frequency is being reported

prevalence

when calculating cumulative incidence (risk), the denominator should include people who already have the health outcome at the beginning of the observation period (T/F)

false

public health officials in Brazil are concerned about an unusually high number of reports of microcephaly among newborns. If they wanted to estimate the rate at which new cases of microcephaly were occurring in the Brazilian population over the next 6 months, which measure of disease frequency is most appropriate

incidence rate

the prevalence of disease is determined by the average duration of disease and the incidence rate of disease (T/F)

true

which of the following statements about cumulative incidence (risk) is NOT true

is it competed based on person-time at risk

a risk difference is the cumulative incidence in the index group minus the cumulative incidence in the reference group (T/F)

true

a risk ratio of 1.87 is equivalent to which of the following estimates

87% increased risk

• = (1.87 - 1.0) x 100 = 0.87 × 100 = 87%

suppose the cumulative incidence (risk) for Group A is 6 cases per 100 participants, and the cumulative incidence (risk) for Group B is 3 cases per 100 participants over the study period. which of the following correctly expresses the risk ratio comparing Group A to Group B

2

• risk A / risk B

• risk A = 0.6

• risk B = 0.3

• 0.6 / 0.3 = 2

a prospective cohort study was conducted over a period of 10 years to ascertain risk factors for coronary heart disease. None of the participants had known coronary heart disease at the beginning of the study. participant A developed coronary heart disease after 6 years of observation. participant B was lost to follow-up after 8 years of observation. Which of the following equals the total person-time at risk for these two participants

14 person-years

• 6 + 8 = 14

a prospective cohort study was conducted in the U.S. during the 2012-2013 influenza (flu) season. The investigators compared the cumulative incidence (risk) of influenza between elderly patients who received the flu vaccine in the fall of 2012 and those who did not. over the course of this flu season, the risk of influenza in the vaccinated group was 60 cases per 1,000 people, and it was 100 cases per 1,000 in the unvaccinated group. which of the following is the best interpretation of the risk ratio comparing the vaccinated group to the unvaccinated group

elderly people who were vaccinated had 0.6 times the risk of influenza compared to those who were unvaccinated during the 2012-2013 US flu season

which of the following is NOT a feature of cohort studies

participants must be randomized at baseline

which of the following is a strength of retrospective cohort studies

cheaper and faster

a special cohort study is appropriate when

the exposure is rare

a prospective cohort study examined the impact of oral health on new onset depression among unhoused people in Boston from 2019-2021. This vulnerable population tends to be dynamic over time. Which of the following relative measures of association would be most appropriate to estimate in this study

incidence rate ratio

what is the purpose of randomization in an experimental study

to minimize confounding

in an experimental study, non-compliance tends to underestimate the true benefit of an intervention (T/F)

true

which of the following is a disadvantage of experimental studies

cannot ethically answer all research questions

what is the purpose of the control group in a case-control study

to estimate the distribution of exposure in the source population

in a case-control study, investigators can directly measure the

odds of disease

in which scenario is it most advantageous to conduct a case-control study

the exposure data is expensive to obtain

the sensitivity of a screening test is the probability that a person without the disease will have a negative test (T/F)

false

specificity focuses on the probability that non-diseased subjects will be classified as non-diseased by the screening test (T/F)

true

the positive predictive value of a screening test refers to the probability that a person who screens positive will actually have the disease (T/F)

true

for a reasonably normal population distribution variability is best described by the standard deviation (T/F)

true

which of the following is the best way to indicate the central tendency for values in a unimodal skewed distribution

median

the standard normal distribution always has a mean value of 0 and a standard deviation value of 1 (T/F)

true

for an individual value in a normal distribution z-score represents which of the following

how many standard deviations the value is away from the mean

a percentile is the value in a normal distribution that has a specific percentage of observations below it (T/F)

true

the appropriate way to estimate the variability in a normally distributed mean from a sample is which of the following

the standard error (SE)

a confidence interval is the point estimate ± the margin of error (T/F)

true

if a p-value is less than 0.05, the groups being compared are definitely different (T/F)

false

p-values indicate the precision of an estimate of effect (risk ratio, difference in means, etc) (T/F)

false

a two dependent sample t-test (or paired t-test) should be used to compare means when the samples are paired or matched, for example, comparing systolic blood pressures in a sample of 20 people before and after they were given a drug intended to lower their blood pressure (T/F)

true

a randomized clinical trial was conducted to compare mean weight loss one year after randomly assigning subjects to a Mediterranean diet or the South Beach diet, which of the following would be the best statistical test for this comparison

two independent samples t-test

a pilot study was conducted in a sample of 30 people to determine the effect of an exercise and diet regimen on body weight after a six month observation period. Each participant's weight was recorded at the beginning of the observation period and at the end of follow-up, which of the following would be the appropriate statistical test for this comparison

two dependent sample or paired t-test

study 1 was conducted with 20 participants with chronic obstructive pulmonary disease (COPD). Participants were randomly assigned to use an inhaler with the new drug or an inhaler containing a placebo. the goal of the study was to determine whether patients randomized to the new medication have a respiratory function that differs from patients randomized to a placebo. the two independent sample t-test yielded a p-value of 0.1, which of the following statements best characterize the conclusion of the study 1

fail to reject the null hypothesis

simply stated, for a two independent sample t-test the null hypothesis is that the groups being compared have equal means (T/F)

true

investigators wanted to use the results of the weymouth health survey to determine whether mean systolic blood pressure was higher in people who were obese or overweight compared to people with a normal body mass index (BMI) in the range of 20-24.99, which of the following would eb the appropriate statistical test for this comparison

one tailed two independent sample t-test

if the null value lies outside of the 95% confidence interval for a two tailed t-test, then the p-value must be less than 0.05 (T/F)

true

a t-test takes into account which of the following

magnitude of difference between the groups being compared and variability within the samples

for which of the following data types is a chi-squared test NOT appropriate

continuous

which of the following is correct as a statement of the null hypothesis for a chi-squared test comparing the frequency of an outcome among two or more exposure groups

the distribution of the outcome is the same among the exposure groups

for each of the measures of association shown, which one correctly states the null hypothesis

risk difference = 0

a chi-squared analysis is to be performed for a study in which there are two possible outcomes and 5 exposure categories. What is the number of degrees of freedom (df)

4

• 5 - 1 = 4

which statement is true regarding risk ratios and odds ratios

a log transformation of risk ratios and odds ratios tends to give a normal distribution, and this is used to compute confidence intervals for risk ratios and odds ratios

a cohort study examines the association between pesticide exposure and prostate cancer among men in the US. The researchers estimate a risk ratio of 1.3 with a 95% CI (1.1, 1.5). therefore, we can conclude that there is a statistically significant association between pesticide exposure and prostate cancer among men in the US (T/F)

true

a randomized clinical trial examines the effect of Ivermectin (FDA approved drug) and mortality among COVID-19 patients. the study finds that Ivermectin, compared to a placebo has a reduces the risk of mortality by 15%. (RR = 0.85 and the 95% confidence interval is between 0.65 and 1.05.) which of the following is true regarding the p-value when examining the effect of Ivermectin (vs. placebo) on mortality among COVID-19 patients

the p-value is greater than 0.05

a researcher designs a randomized clinical trial in which half of the participants are assigned to a placebo and the other half are assigned to a diuretic to examine the effect on their systolic blood pressure (measure in mmHg - a continuous outcome). which hypothesis test should be used to determine if the mean systolic blood pressure is equal for those assigned to a placebo versus those assigned to a diuretic

two independent sample t-test

a researcher designs a randomized clinical trial in which half of the participants are assigned to a placebo and the other half are assigned to a diuretic to examine the effect on their hypertension status (participants are classified as hypertensive or not hypertensive - a dichotomous outcome). which hypothesis test should be used to determine if the risk for hypertension is the same for those assigned to a placebo versus those assigned to a diuretic

chi-squared test of independence

investigators in the Framingham Heart study designed a cohort study to examine the association between BMI (an ordinal variable defined as: 1) <18, 2) 19-24, 3) 25-29 and 4) ≥30) and the development of type 2 diabetes over a 20 year period (an ordinal variable defined as: 1) did not develop diabetes, 2) pre-type 2 diabetic and 3) developed type 2 diabetes). if they use a chi square test to determine if there is an association how many degrees of freedom are associated with the chi square statistic

6

• (r - 1) x (c - 1)

• r = 4

• c = 3

• (4 - 1) x (3 - 1) = 3 × 2 = 6