1. The Variable Explosion Or how the DDI variable spread out to inhabit multiple modules in DDI 3.0

2. Once there was a mild mannered DDI 1.0 variable What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

3. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

4. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

5. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

6. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

7. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

8. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

9. It was well contained and kept close to home What country were you born in? Nativity 1 Native 798920 2 Foreign 210023 Place_of_Birth If US code as 1, else code as 2

10. By 2.1 it has gotten a bit bolder You could arrange the variables into nCubes creating multidimensional structures It now had an optional place to put data location information In allowed for more explicit nesting and category structure

11. Then along came 3.0 and things got exciting

12. Modularity ruled! Concepts were captured early Questions developed and linked to concepts Categories were defined… …and grouped into specific relationships Variables were created using these category groups Data storage was designed Physical instances of data files were created and summary statistics calculated

13. Fortunately they all hung on to their “handies” and stayed in touch…

14. Implications for creating documentation You can create in the order that information becomes available You can reuse pieces and imply relationships Support community wide concept, question, category and variable banks Create new physical instances or formats without changing other modules

15. It requires Thinking about a variable as a development process rather than as an artifact New tools to facilitate information capture and create the appropriate links

16. Building A Variable

17. Categories Individual labels and definitions Comparability is by definition NOT by label Can be used by multiple Category Groups

18. Category Groups A category group is made up of 1 or more categories Flat – no hierarchies Hierarchical - Levels Regular Irregular Provides specific category codes

19. Variable construction Variable No categories Ranges Open Category Groups Full Level Discrete Range Cherry pick

20. NCube They grew up, got a capital N Still composed of one or more variables Provide for multiple measures Gained features to make them comparable to SDMX structures

21. What have we got Logical product Categories Category Groups [name may change to protect the innocent] Assembled into variables Variables assembled into NCubes Concepts, questions, physical location and summary stats are in other modules