USMLE Step 1 Biostatistics/Epidemiology Study Guide Solutions

USMLE Step 1 Biostatistics/Epidemiology Study Guide Solutions Sensitivity - ANSWER-TP / (TP + FN) Specificity - ANSWER-TN / (TN + TP) Positive Predictive Value - ANSWER-TP / (TP + FP) Negative Predictive Value - ANSWER-TN / (FN + TN) Incidence Rate - ANSWER-# of new cases in a certain time period / population that is at risk during that time period This looks at new incidences occurring during a time period Prevalence - ANSWER-# of existing cases / population at risk Looks at ALL current cases ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED FIRST PUBLISH OCTOBER 2024 Page 2/6 Odds Ratio - ANSWER-(a/c) / (b/d) OR ad / bc Relative Risk - ANSWER-[a / (a + b)] / [c / (c + d)] Attributable Risk - ANSWER-(a / (a+b) ) - (c / (c+d) ) Gaussian curve standard deviation %'s - ANSWER-+/- 1 SD = 68% +/- 2 SD = 95% +/- 3 SD = 99.7% Type 1 error (alpha) - ANSWER-you sAw a difference that did not really exist (convicting an innocent man) Type 2 error (beta) - ANSWER-you were Blind to a difference that did exist (setting a guilty man free) Power - ANSWER-1-beta or in other words, 1 - type 2 error (increasing sample size will increase power, there is POWER in numbers. Also, increasing Precision will increase power) SEM - ANSWER-SD / square root of n ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED FIRST PUBLISH OCTOBER 2024 Page 3/6 Confidence Interval - ANSWER-range from [mean - Z (SEM)] to [mean + Z (SEM)] Z = 1.96 for 95% CI Z = 2.58 for 99% CI On the test, it may be easier to remember the Z values as 2 and 2.5 for easier calculations and memorization t - test - ANSWER-checks difference between the means of 2 groups