USMLE: Public Health Sciences
With 100% Correct Answers 2024
What number is in the denominator for the RATE of divorce? - correct answer Per 100
marriages
What number is in the denominator for the RATE of infant mortality? - correct answer
Per 1000 live births
What is the typical RATE given in epidemiology for most cases? - correct answer Per
100,000.
What are most disease rates in the US for most all diseases? - correct answer Less
than 50 per 100,000.... Almost ALL are below 100 per 100,000
What is an INCIDENCE rate? - correct answer The rate of NEW cases in a population
divided by people at risk to be a case
What is a PREVALENCE rate? - correct 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? - correct answer IN-cidence is the rate
of new IN-coming cases
What type of rates should be associated with Incidence? - correct 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? - correct answer Point and
Period prevalence
What is point prevalence? - correct answer A particular INSTANCE in time....Who has
the disease over who is at risk.
,USMLE: Public Health Sciences
With 100% Correct Answers 2024
What is period prevalence? - correct 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? - correct answer Incidence data....the
number of newly dead
What is the general relationship between prevalence and incidence? - correct answer
Prevalence = incidence x duration....
If either incidence or duration increase, so does prevalence.
What is a CRUDE rate? - correct answer A rate that is generalized to an entire
population, ie death rate in the US in 2000
What is a SPECIFIC rate? - correct 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? - correct 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? - correct answer Deaths from a cause (heart
disease) divided by all deaths.
Sensitivity detects what?? - correct 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?? - correct answer HEALTHY people!! True negatives over all
people without the disease (TN+ FP)
What does PPV detect? - correct 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
,USMLE: Public Health Sciences
With 100% Correct Answers 2024
What does NPV detect - correct 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? - correct answer TP + TN over
EVERYTHING, TP FP TN and FN
As prevalence increases what happens to positive and negative predictive values? -
correct 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.... - correct answer Dur.
What is the relationship between pretest probabilities of sensitivity and sensitivity WRT
prevalence? - correct answer NONE...Pretest values are constant and are a measure of
the test itself, and will never change.
What point of the double hump diagram gives you the FEWEST FALSES or the highest
accuracy for a test? - correct answer The point where the two curves cross...To move
either direction gives you a few fewer falses in one category but a whole bunch more
falses in another direction.
What is the FIRST thing you need to do when constructing a 2x2 table for the USMLE?
- correct answer Pick a total population number and anchor is with PREVALENCE
before plugging in numbers. Prevalence is the number of people in the population with
disease, so for 100 people and prevalence of 20 % is 20 with disease 80 without....Then
plug in the corresponding Sensitivities and Specificities.
, USMLE: Public Health Sciences
With 100% Correct Answers 2024
What are the four study design questions asked on USMLE questions? - correct 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 - correct answer Precision... same result every time
CAN have no validity tho.
Validity is equal to - correct answer Accuracy....
Validity implies.... - correct answer Reliability... but the opposite is not always true.
What is a selection bias? - correct 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? - correct 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? - correct 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? - correct 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? - correct answer The fact of observation ITSELF
changes the activity of those observed...To meet the expectations of the researcher
With 100% Correct Answers 2024
What number is in the denominator for the RATE of divorce? - correct answer Per 100
marriages
What number is in the denominator for the RATE of infant mortality? - correct answer
Per 1000 live births
What is the typical RATE given in epidemiology for most cases? - correct answer Per
100,000.
What are most disease rates in the US for most all diseases? - correct answer Less
than 50 per 100,000.... Almost ALL are below 100 per 100,000
What is an INCIDENCE rate? - correct answer The rate of NEW cases in a population
divided by people at risk to be a case
What is a PREVALENCE rate? - correct 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? - correct answer IN-cidence is the rate
of new IN-coming cases
What type of rates should be associated with Incidence? - correct 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? - correct answer Point and
Period prevalence
What is point prevalence? - correct answer A particular INSTANCE in time....Who has
the disease over who is at risk.
,USMLE: Public Health Sciences
With 100% Correct Answers 2024
What is period prevalence? - correct 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? - correct answer Incidence data....the
number of newly dead
What is the general relationship between prevalence and incidence? - correct answer
Prevalence = incidence x duration....
If either incidence or duration increase, so does prevalence.
What is a CRUDE rate? - correct answer A rate that is generalized to an entire
population, ie death rate in the US in 2000
What is a SPECIFIC rate? - correct 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? - correct 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? - correct answer Deaths from a cause (heart
disease) divided by all deaths.
Sensitivity detects what?? - correct 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?? - correct answer HEALTHY people!! True negatives over all
people without the disease (TN+ FP)
What does PPV detect? - correct 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
,USMLE: Public Health Sciences
With 100% Correct Answers 2024
What does NPV detect - correct 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? - correct answer TP + TN over
EVERYTHING, TP FP TN and FN
As prevalence increases what happens to positive and negative predictive values? -
correct 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.... - correct answer Dur.
What is the relationship between pretest probabilities of sensitivity and sensitivity WRT
prevalence? - correct answer NONE...Pretest values are constant and are a measure of
the test itself, and will never change.
What point of the double hump diagram gives you the FEWEST FALSES or the highest
accuracy for a test? - correct answer The point where the two curves cross...To move
either direction gives you a few fewer falses in one category but a whole bunch more
falses in another direction.
What is the FIRST thing you need to do when constructing a 2x2 table for the USMLE?
- correct answer Pick a total population number and anchor is with PREVALENCE
before plugging in numbers. Prevalence is the number of people in the population with
disease, so for 100 people and prevalence of 20 % is 20 with disease 80 without....Then
plug in the corresponding Sensitivities and Specificities.
, USMLE: Public Health Sciences
With 100% Correct Answers 2024
What are the four study design questions asked on USMLE questions? - correct 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 - correct answer Precision... same result every time
CAN have no validity tho.
Validity is equal to - correct answer Accuracy....
Validity implies.... - correct answer Reliability... but the opposite is not always true.
What is a selection bias? - correct 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? - correct 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? - correct 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? - correct 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? - correct answer The fact of observation ITSELF
changes the activity of those observed...To meet the expectations of the researcher
