Public health science USMLE step 1. Exam Questions With Correct Answers
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Course
USMLE
Institution
USMLE
Public health science USMLE step 1. Exam
Questions With Correct Answers
What number is in the denominator for the RATE of divorce? - answerPer 100 marriages
What number is in the denominator for the RATE of infant mortality? - answerPer 1000 live
births
What is the typical RATE given in epidem...
Public health science USMLE step 1. Exam
Questions With Correct Answers
What number is in the denominator for the RATE of divorce? - answer✔✔Per 100 marriages
What number is in the denominator for the RATE of infant mortality? - answer✔✔Per 1000 live
births
What is the typical RATE given in epidemiology for most cases? - answer✔✔Per 100,000.
What are most disease rates in the US for most all diseases? - answer✔✔Less than 50 per
100,000.... Almost ALL are below 100 per 100,000
What is an INCIDENCE rate? - answer✔✔The rate of NEW cases in a population divided by
people at risk to be a case
What is a PREVALENCE rate? - answer✔✔The rate of ALL cases in a population divided by
people at risk to be a case.
How do you remember was an incidence rate is? - answer✔✔IN-cidence is the rate of new IN-
coming cases
What type of rates should be associated with Incidence? - answer✔✔Attack rate---you shrink the
denominator as per the exposure.
Create a difference 'attack rate' for every food that was eaten in a restaurant, saw, and the one
with the highest rate is the culprit. (Acute conditions)
What two prevalences are associated with prevalence rate? - answer✔✔Point and Period
prevalence
What is point prevalence? - answer✔✔A particular INSTANCE in time....Who has the disease
over who is at risk.
What is period prevalence? - answer✔✔Period is for a larger period of time, who has it over this
period over who is at risk
Mortality data is by definition what type of date? - answer✔✔Incidence data....the number of
newly dead
What is a CRUDE rate? - answer✔✔A rate that is generalized to an entire population, ie death
rate in the US in 2000
What is a SPECIFIC rate? - answer✔✔One that has been modified to have some sort of
qualifier, ie male death rate in 2000... This is GENDER SPECIFIC
What is a CASE fatality rate? - answer✔✔The number of deaths from a specific cause (heart
disease) divided by the number of patients with that disease.
What is the Proportionate mortality rate? - answer✔✔Deaths from a cause (heart disease)
divided by all deaths.
Sensitivity detects what?? - answer✔✔DISEASE! The calculation deals with diseased people.
They actually HAVE the disease.... So it is true positives divided by the rest, True positives over
(TP and the false negatives)
Specificity detects what?? - answer✔✔HEALTHY people!! True negatives over all people
without the disease (TN+ FP)
What does PPV detect? - answer✔✔The value of a positive test result and of course is given by
the TRUE's divided by everything in the row. True positives divided by all positives, TP AND
FP
What does NPV detect - answer✔✔The value of a negative test result, given by the TRUE
negatives divided by all the negatigves, TN and FN
How do you calculate the ACCURACY of a test? - answer✔✔TP + TN over EVERYTHING,
TP FP TN and FN
As prevalence increases what happens to positive and negative predictive values? -
answer✔✔PPV goes up. More people have the disease, thus a + test result is more believable.
NPV goes down. More people have the disease, fewer people are without it so a negative is less
likely.
There are NO direct changes on a screening test based on increased or decreased incidence.... -
answer✔✔Dur.
What is the relationship between pretest probabilities of sensitivity and sensitivity WRT
prevalence? - answer✔✔NONE...Pretest values are constant and are a measure of the test itself,
and will never change.
What are the four study design questions asked on USMLE questions? - answer✔✔What type of
bias is there, if any?
How would you fix the bias, if any?
What type of study design is this?
How would you analyze data from this study?
Reliability is equal to - answer✔✔Precision... same result every time
CAN have no validity tho.
Validity is equal to - answer✔✔Accuracy....
Validity implies.... - answer✔✔Reliability... but the opposite is not always true.
What is a selection bias? - answer✔✔Where there is a nonrandom assignment to the study
group... ie to study the fitness of people in NY you go to 10 local gyms in NY and take
measurements....
What is selection bias AKA? - answer✔✔Sampling bias
Berkson's bias (using hospital records to estimate population parameters)
Non-respondent bias--ALWAYS a problem, because this is based on people who VOLUNTEER,
which is mandatory for study groups.
(a convenience sample)
What is the way to fix selection bias? - answer✔✔Take a random sample or selection and weight
the data to make sure it matches the population if there are any discrepancies
What is measurement bias? - answer✔✔Asking leading questions that suggest in word voice
tone what the bias of the asker of the questions is.
What is the Hawthorne effect? - answer✔✔The fact of observation ITSELF changes the activity
of those observed...To meet the expectations of the researcher
What is the expectancy effect AKA? - answer✔✔The Pygmalion effect
What is the Pygmalion effect? - answer✔✔Occurs when a researcher's beliefs in the efficacy of
treatment changes the outcome of that treatment.
What is the treatment of the Experimenter Expectancy Bias, or Pygmalion effect? -
answer✔✔Double blind studies, so neither the subject NOR the researcher knows which group is
which.
What is the problem with Lead-Time bias? - answer✔✔Confusing or stating that early detection
leads to an increased survival rate...That patient might very will die at the same time they would
have anyway, they just knew about their disease longer.
How do you fix lead time bias? - answer✔✔Don't use the number of years survival after
diagnosis as a measurement of benefit---Use life expectancy instead!
What is recall bias? - answer✔✔When a patient does not accurately recall what happened in the
past, often clouded by their current knowledge or mindset.
How do you fix recall bias? - answer✔✔CONFIRM or TRIANGULATE what is told to you...
What is late-look bias? - answer✔✔Gathering information at an inappropriate time...You for the
symptoms and severity of a disease, by interviewing patients with the disease but those with the
worst cases are too sick or dead and cannot be interviewed...leads to a healthier outlook on the
disease.
How do you fix late-look bias? - answer✔✔Stratify be severity! Make sure that you have people
representing each stage of a disease so as not to leave anyone out.
What is confounding bias? - answer✔✔Occurs when the research is complicated by the fact that
there is more than one factor affecting the outcome of your study...The effect of one can distort
or confuse the effect of the other...
How is confounding bias eliminated or fixed? - answer✔✔Do multiple studies or do Meta-
Analysis.
What is a design bias?? - answer✔✔Using two non-comparable control groups...ie having one
group of hypertensives on a drug and giving a group of normotensives a placebo...
How do you fix design bias? - answer✔✔Random ASSIGNMENT of participants into groups
How do you know you are looking at a Case-Report? - answer✔✔There is one single
subject....Difficult to differentiate their own personal baggage from the disease.
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