# Pca and utility

## 19 important questions on Pca and utility

### What do you essentially do with a factor analysis on a test?

### How do you perform a factor analysis?

- Go to analyse, dimension reduction, factor
- put all the questions into variables
- extraction; select principle axis factoring for method, check scree plot (after looking at the scree plot, select fixed number of factors; amount of factors)
- rotation; select direct oblimin,
- options; press sorted by size, (optional;) suppress small coefficents .3, do this just know that some values will not be shown.

### What does the table of total variance explained tell us?

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### In a scree plot, where is the point of inflection?

### How can you tell the amount of factors from a scree plot?

### What do do after you've determined the amount of factors you have?

### What can you see in the pattern matrix?

- You can see which questions form a cluster together
- which questions belong to which factor
- what the overarching theme of a factor is.

### What are the advantages and disadvantages of the classical test theory?

- Intuitive and easy to apply
- It is in SPSS and it is easy to do in excel
- No large sample sizes/many items needed

- – Focus on the test, not on the items
- – Test properties depend on the population
- E.g.,: Reliability and difficulty of a test
- Person properties depend on the test
- I.e., sum score is higher if the test is easy and lower if the test is difficult

### What do you do when using the item response theory?

### What are the assumptions of the item response theory?

- Uni-dimensionality; you only measure one construct
- local independence; the latent trait explains all item correlations
- monotonicity; the higher the trait the higher the expected score.

### How can you tell the item difficulty from an item characteristic curve?

### How can you tell the item discrimination from the item characteristic curve?

### From the results of an item response analysis, how do you know which items are weak?

### At which point of the item characteristic curve is the most information?

### What is a scale information function?

### How can you tell that items are unfair towards certain groups?

### What is computerized adaptive testing

- Instead of giving everyone the same items and the whole range of difficulty
- computerized adaptive testing will adjust difficulty of the next item based on the answer of the last item.

### How does the computer pick new questions in computerized adaptive testing

- Based on the information of the last question, and estimate is calculated of the extend to which the trait is present
- the next question is picked to have the highest information on that degree of trait presence

### What are the advantages and disadvantages of item response theory

- Population and test independent
- Focus on items

- Statistical complex
- Needs large samples

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

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