Based on my prior knowledge, the size of the luggage boot (lug_boot) in a car can have an impact on the decision to buy the car. Here's the analysis of the relationship between the feature and the target (decision to buy the car):

- For the "unacceptable" rating: It is likely that cars with a "small" lug_boot would be considered unacceptable, as they may not provide enough space for luggage.
- For the "acceptable" rating: Cars with a "med" (medium) lug_boot may be seen as acceptable, as they provide a moderate amount of space for luggage.
- For the "good" rating: Cars with a "big" lug_boot are more likely to be considered good, as they offer ample storage space.
- For the "very good" rating: It is possible that having a larger lug_boot size, such as "big", would contribute to a very good rating.

Based on this analysis, the dictionary format would be as follows:

```json
{
	"unacceptable": ["small"],
	"acceptable": ["med"],
	"very good": ["big"],
	"good": ["big"]
}
```

Please note that this analysis is based on prior knowledge and assumptions, and it may not accurately reflect the true relationship between the lug_boot feature and the decision to buy the car. Further analysis and data exploration would be necessary to validate these assumptions.