USMLE Step 1 Behavioral Science – Complete Exam Study Guide 2026/2027 with Verified Answers | Newest Version. A+

USMLE Step 1 Behavioral Science

Rate formula & key points ------- ✔ CORRECT ANSWER ✓✓Actual cases/Potential cases = RATE



Denominator is key*

(Who is at risk?)



RATE is normally = per 100,000 cases (cases of people at risk; denominator)



*Important point*: Most (95%) cases in the US for diseases are under 50/100,000, at most
100/100,000



Incidence vs Prevalence differentiation ------- ✔ CORRECT ANSWER ✓✓Incidence (acute
conditions): NEW cases/population at risk (people who never got the disease, etc.)



Prevalence (chronic conditions): ALL cases/population at risk



Differentiation:

- If individual already has the disease, he cannot be at risk for incidence; he is already 'sick';
incidence only applies to NEW cases

- Prevalence applies to ALL cases, people who had the infection, people who had the infection
and healed, people who just got the infection in a period of time; chronicity



Attack rate ------- ✔ CORRECT ANSWER ✓✓Incidence



type of incidence rate in which the denominator is further reduced for some known exposure

,100 people goes to a italian restaurant

50 people ordered pasta

20 people of the 50 who ordered pasta got sick



general incidence rate = 20/100



specific incidence rate with attack rate involved = 20/50




Exposures with the highest attack rate ratio will most likely be the source of cause



Relationship formula: prevalence and incidence ------- ✔ CORRECT ANSWER ✓✓Prevalence =
Incidence x Duration



P=IxD



Morbidity rate ------- ✔ CORRECT ANSWER ✓✓rate of disease in population at risk; refers to
both incident and prevalent cases



Mortality rate ------- ✔ CORRECT ANSWER ✓✓rate of death in a population at risk refers to
incident cases only



mortality refers to the 'NEWLY' dead, due to cause of the onset of a NEW infection



Prevalence Pot ------- ✔ CORRECT ANSWER ✓✓Reservoir = population at risk

,As the population at risk develops onset of disease, it is categorized as incidence rate



Over time, the accumulation of incidence rate disease becomes the prevalence cases of
chronicity



Prevalence cases either recovers or dies (mortality; incidence)



Incidence vs. Prevalence situations: ------- ✔ CORRECT ANSWER ✓✓



Incidence vs. Prevalence situations: 2nd portion ------- ✔ CORRECT ANSWER ✓✓



AIDS cases graph readings: incidence rate + prevalence rate + point prevalence ------- ✔
CORRECT ANSWER ✓✓1990~1991 Incidence rate + Prevalence rate



I = 4/6

(onset = 3, 4, 6, 9; at risk= 3, 4, 6, 8, 9, 10)



P = 7/9

(all cases within 1990~1991 = 1, 3, 4, 5, 6, 7, 9; at risk group = only person NOT at risk is 2 due to
death before period of inspection)



Point prevalence rate of 1/1/1991

PP = 4/6

(all cases on 1/1/1991 = 3, 4, 7, 9; at risk is anyone that did NOT die before 1/1/1991 = 3, 4, 7, 8,
9, 10)



Crude rate = ? ------- ✔ CORRECT ANSWER ✓✓for the whole population

, almost never use this; due to almost impossible comparison of 2 population with equal points



Specific rate = ? ------- ✔ CORRECT ANSWER ✓✓for the sub-group of the population



gender-specific

age-specific

nationality-specific



Adjusted rate/Standardized rate = ? ------- ✔ CORRECT ANSWER ✓✓getting clean comparison



to adjust 2 groups of different demographics/race/gender/age etc. to the same level for a better
comparison



Men vs. woman in MI

- better as age-adjusted data



White vs. Blacks in stomach cancer

- better as age-adjusted data



How to interpret date: Physicians are more likely to commit suicide in the U.S. ------- ✔
CORRECT ANSWER ✓✓First reaction: stress, access to pharmaceuticals, long working
hrs.....WRONG



First correct reaction is to see the type of data it is



It is known study people of higher SES is more likely to commit suicide vs. people of lower SES