Probability

Independence: across Multiple Events

1. Combine by multiplication if independent

2. multiply the probability of one event by the probability of the 2nd

e.g. if a box has 5 white balls and 5 black balls, the chance of picking 2 black balls is (5/10) x (4/9) = 0.5 x 0.44 = 0.22 (or 22%)

Mutually Exclusive: within a single event

combine by Addition [A+B]

if not mutually exclusive (to find out the intersected area)

• add two together and substract out multiplied probabilities [ A+B - (AB) ]

• Positive and negative predictive values are prevalence dependent. Likelihood ratios are not prevalence dependent

Intention to treat analysis is a method of analysis for randomized controlled trials in which all patients randomly assigned to one of the treatments are analysed together, regardless of whether or not they completed or received that treatment

Intention to treat analysis is done to avoid the effects of crossover and drop-out, which may affect the randomization to the treatment groups

significance tests

The type of significance test used depends on whether the data is parametric (something which can be measured, usually normally distributed) or non-parametric

Parametric tests

• Student's t-test - paired or unpaired*