# How do you interpret the likelihood ratio?

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## How do you interpret the likelihood ratio?

Likelihood ratios (LR) in medical testing are used to interpret diagnostic tests. Basically, the LR tells you how likely a patient has a disease or condition. The higher the ratio, the more likely they have the disease or condition. Conversely, a low ratio means that they very likely do not.

### What does Wald mean in logistic regression?

It is similar to a standard deviation to a mean. Wald χ2– This is the test statistic for the individual predictor variable. A multiple linear regression will have a t test, while a logistic regression will have a χ2 test. This is used to determine the p value.

#### What does a significant LRT mean?

If (and only if) this pertains to a Likelihood Ratio test between two models (fitted by likelihood maximization techniques), a significant test would mean the ‘alternative’ model has a better fit (read: higher likelihood) on your data than the ‘null hypothesis’ model (see Michael Chernick’s comment).

**What does a Wald test do?**

The Wald test (also called the Wald Chi-Squared Test) is a way to find out if explanatory variables in a model are significant. If the Wald test shows that the parameters for certain explanatory variables are zero, you can remove the variables from the model.

**What does a positive likelihood ratio mean?**

[4] A positive likelihood ratio, or LR+, is the “probability that a positive test would be expected in a patient divided by the probability that a positive test would be expected in a patient without a disease.”.

## What is positive likelihood ratio?

Likelihood ratios (LR) are used to express a change in odds. They are used most often in the realm of diagnosis. The positive likelihood ratio (+LR) gives the change in the odds of having a diagnosis in patients with a positive test. The change is in the form of a ratio, usually greater than 1.

### What is the null hypothesis for likelihood ratio test?

The likelihood ratio test is a test of the sufficiency of a smaller model versus a more complex model. The null hypothesis of the test states that the smaller model provides as good a fit for the data as the larger model.

#### What is the null hypothesis for Wald test?

The Wald test works by testing the null hypothesis that a set of parameters is equal to some value. In the model being tested here, the null hypothesis is that the two coefficients of interest are simultaneously equal to zero.

**How is the likelihood ratio test statistic calculated?**

Now that we have both log likelihoods, calculating the test statistic is simple: So our likelihood ratio test statistic is 36.05 (distributed chi-squared), with two degrees of freedom.

**How can I perform the likelihood ratio and Wald test in?**

In general, both tests should come to the same conclusion (because the Wald test, at least in theory, approximate the LR test). As an example, we will test for a statistically significant difference between two models, using both tests.

## Where can I get a copy of likelihood ratios?

Address correspondence and requests for reprints to Dr. McGee: University of Washington Seattle-Puget Sound VA Health Care System (S-111 GIMC), 1660 S. Columbian Wy., Seattle, WA 98108 (e-mail: [email protected]). Copyright2002 by the Society of General Internal Medicine

### Which is the likelihood ratio of the χ2 distribution?

The likelihood ratio test statistic is also compared to the χ2 distribution with (r − 1)(c − 1) degrees of freedom. This statistic is also given at the bottom of Table 12.10, and is seen to be almost exactly equal to the “usual” χ2 statistic.