Educational Videos

So you want to learn about testing?

These videos were created by doctors and epidemiologists with expertise in evidence-based diagnosis and education.

Watching episodes 1-6 is equivalent to most medical school classroom content in <25 minutes.

Videos expand the focus from teaching definitions to cover the missing link of how to translate the science of tests and testing into real life clinical decisions.

Locate specific terms and ideas in each video for review in the contents section.

Episode 1: How to Approach Testing

Summary: Learn how to think about testing in clinical medicine using probability and how to quantify uncertainty. Understand the diagnostic process, when to order and how to interpret a test.

Contents

Definition of a test (0:10) | Probability & Uncertainty (0:38) | 3 Ps for diagnosis (1:04) | Interpreting pos/neg results (1:36) | Treatment threshold (2:30) | Pros & Cons of testing (2:43) | Shared-decision making for testing (3:19)

Episode 2: Pretest Probability

Summary: Diagnosis relies on accurately estimating the chance of disease in patients before testing is done known as pretest probability. Estimate pretest probability based on 1) disease incidence, 2) history, 3) exam.

Contents

Example: cardiac ischemia (0:52) | Example: HIV (1:31) | Diagnostic ”zebras” (2:14) | Testing thresholds (2:24) | Treatment thresholds (2:40) | Best situations to test (3:00)

 

 

 

Episode 3: Sensitivity & Specificity

Summary: Learn the measures for how well a test works: sensitivity and specificity. See how these numbers are generated and translate them into how often a test is inaccurate in the form of false-negatives and false-positives.

Contents

Sensitivity (0:45) | False-negatives (misses) (1:06) | Specificity (1:16) | False-positives (1:40) | Example: cardiac ischemia (2:07) | Example: HIV (2:38)

 

 

 

Episode 4: How to Calculate the Meaning of a Positive or Negative Test Result

Summary: Updating the pretest probability after a positive or negative test result gives the positive or negative predictive value. Learn how to estimate this intuitively using natural frequencies.

Contents

Natural frequencies (0:55) | Sensitivity to identify disease (1:39) | Specificity to identify well patients (2:03) | Positive predictive value (2:16) | Negative predictive value (2:50)

 

 

 

 

 

 

Medical Testing in Practice 1

Summary: To make diagnoses in patients, doctors must consider the consequences of testing. We consider a case of heart failure starting with pretest probability, the meaning of a positive or negative test and the pros and cons of testing.

Contents

Pros and Cons of testing (0:13) | Example: Heart failure (0:42) | BNP test, low and high positive results (1:23) | Changing test cutoff values (1:48) | Risk of false-negatives (2:02)

 

 

 

 

 

 

 

 

 

Medical Testing in Practice 2

Summary: In clinical medicine doctors often have to decide between multiple tests. A patient with possible pulmonary embolism is discussed with consideration of D-dimer and CT scan tests. Sequential testing is described as a way to optimal test characteristics.

Contents

Example: Pulmonary Embolism (0:17) | Tests for Pulmonary Embolism (0:44) | Sequential testing (2:14)

 

 

 

 

 

 

How Testing Can Go Wrong

Summary: In clinical medicine doctors must often decide among multiple tests. We discuss a patient with possible pulmonary embolism with consideration of D-dimer and CT scan tests. Sequential testing is described as a method to optimize test performance.

Contents

History of testing (0:36) | False-positives (1:51) | Rare diseases (2:58)