# Prediction Models

## 13 important questions on Prediction Models

### What is the problem with both selection methods?

### When are variables kept or deleted in fw or bw selection?

-->if Pentry DIFFP removal then FW and BW selections lead to DIFF models

### Events per Variable Problem

How to solve that?

10/15 people *each prediction variable(dof)

- Higher grades + faster learning
- Never study anything twice
- 100% sure, 100% understanding

### Quality of Prediction model, how to assess that?

•Explained variance(R2, values 0-100%, the higher the better)

•Calibration(=agreement between predicted probabilities of outcome and observed outcome)

•Discrimination(= how well the model can distinguish between the people who have the outcome and those who don't)

### What types of calibration are there?

Calibration curve - predicted probabilities against observed probabilities. Ideally in a linear line. scale is 0,1 in both x and y

Hosmer and Lemeshow- agreement predicted and expected numbers

### What is the linear predictor?

### Calibration slope and what can you use it for?

It is used to correct overfitting(optimism) of the regression coefficient.

### What is the shrinkage factor?

### Why do you need to adjust the regression coefficient?

### Internal validation of Prediction model

- Internal validation is important to obtain a honest estimate of performance for patients that are similar to those in the development sample

-Methods to internally validate: bootstrapping-estimation optimism-adjustment slope accordingly.

### External Validation of Prediction model

External validity depends on quality of internal validity and different distribution of predictors/outcome values between development and validation samples

### 3 steps for external validation of Prediction models?

2.Calculation new Linear predictor (LP)= multiply regression coeff with values predictors in external dataset

3. Quality model evaluation (discrimination, calibration)

### What is the wald value?

The question on the page originate from the summary of the following study material:

- A unique study and practice tool
- Never study anything twice again
- Get the grades you hope for
- 100% sure, 100% understanding