Evidence Based Medicine pills
Evidence Based Medicine pills
Occasionally, among the primary studies in a meta-analysis, there may be some that, without estimating an excessively large or small effect, can have a significant influence on the overall estimate of the study, thus compromising its robustness. These are referred to as influential studies, or more commonly, influencers. The distinction between these and outlier or extreme studies is described, as well as the most commonly used methods for detecting them.
The fixed-effect model (singular) is used to combine the primary studies in a meta-analysis when it is assumed that all studies estimate the same population effect. The fixed-effects model (plural), also called mixed-effects model, is useful for subgroup analysis within a meta-analysis, combining aspects of the fixed-effect and the random-effects models.
Many diagnostic tests are based on statistical models that predict the probability that a given subject will be positive for that test. Although the ROC curve evaluates the overall performance of the test, the choice of the probability threshold to differentiate between positives and negatives will condition the performance of the test in a given clinical scenario.
The binomial distribution is used when we want to calculate the probability of obtaining a certain number of successes in a series of Bernoulli trials, assuming we already know the probability of success in each trial. In contrast, the beta distribution is used in the opposite situation: we have observed a given number of successes and failures, and we want to estimate how likely each possible value of the success probability is. In other words, it allows us to update our beliefs about that probability based on the data we have collected.
The rationale for minimizing the sum of squared errors in linear regression, which is often presented as a simple choice of convenience, is discussed. A probabilistic perspective suggests that the least squares equation arises naturally from assuming that the model's residuals follow a normal distribution.