MA123 – Project 1: Probability (Report)
Name: ____________________________________ Score: ____ pts.
This project relates to concepts in epidemiology with focus on clinical usefulness of diagnostic tests.
Resources (Make sure to review these resources before starting the project):
• Calculating Sensitivity and Specificity using a 2 x 2 table (Click me).
• Calculating Positive and Negative Predictive Values using a 2 x 2 table (Click me).
• Sensitivity, Specificity, PPV, NPV (Click me).
• How to use COUNTIF and COUNTIFS in Microsoft Excel (Click me).
Problem:
A new test to diagnose a Urinary Tract Infection (UTI) in women (patients) is being assessed. The comparison gold
standard is positive urine dipstick plus urine culture. Data collected on this new test are provided in the
accompanying Microsoft Excel file.
Your task:
1. (40 points) Use Microsoft excel function “COUNTIFS” to create a confusion matrix (2 x 2 table) showing
how many true-positives (TP), false-positives (FP), false-negatives (FN), and true-negatives (TN) are in the
study.
Place your confusion matrix here (make sure it is well labeled)
2. Use the confusion matrix created in 1) to answer the following questions.
i. (15 points) What percentage of women (patients) with a positive urine dipstick plus urine culture who
have a positive diagnostic test (TP rate or Sensitivity)?
Provide your answer here
ii. (15 points) What percentage of women (patients) without urine dipstick plus urine culture who have a
negative diagnostic test (TN rate or Specificity)?
Provide your answer here
iii. (10 points) What percentage of women (patients) were correctly diagnosed with a positive test
(Positive predictive value)?
Provide your answer here
iv. (10 points) What percentage of women (patients) were correctly diagnosed with a negative test?
(Negative predictive value)?
Provide your answer here
3. (10 points) Based on the results in 1, and 2 (i, ii, iii, and iv) state your conclusion about the new test to
diagnose a Urinary Tract Infection (UTI) in women (patients). (No more than two sentences).