Research Methodology and Interpretation

1. A patient’s pre-test probability of having a concealed BT is 20%.

2. A maneuver with a positive likelihood ratio of 10 is then positive.

3. What is the approximate post-test probability of the patient having a concealed BT?

1. Convert probability to odds: 0.2/0.8 = 0.25, i.e. (P/1-P)

2. Multiply by positive likelihood ratio: 0.25 × 10 = 2.5 (positive or negative multiplication)

3. Convert back to odds: 2.5/3.5 = 71% (New Odds/New Odds + 1)

Formula for wavelength in terms of refractory period and conduction velocity

Wavelength = RP x CVelocity

*If an AAD increases RP but CV is unchanged, more likely to encounter refractory tissue and reentry is less likely. If we decrease CV but leave RP the same, more viable tissue to be stimulated and reentry is more likely.

Let’s say a town has:

1. Population of 10,000 people

2. 200 people diagnosed with AF as of January 1

3. 50 people diagnosed with AF within the following year

Differentiate between the prevalence of AF as of January 1, the incidence of AF in the year, and the period prevalence of AF in the year.

1. 1. Prevalence is proportion of people who have the condition at specific point in time: 200/10,000 = 2.0% on January 1

2. 2. Incidence counts new cases among people at risk (not yet diagnosed) over a period: 50/(10,000-200) = ~0.5%

3. 3. Period prevalence adds new to existing cases for the time period: 250/10,000 = 2.5%

How to calculate negative likelihood ratio in terms of sensitivity and specificity

Negative likelihood ratio = (1-Sensitivity)/Specificity