6 Qualitative comparative analysis
An intuitive way to identify causality is to search for patterns in the data of which we believe can be interpreted in a causal fashion. The qualitative comparative analysis (QCA) offers a framework to identify, based on set theory, relationships in terms of necessary conditions and sufficient conditions for a specific outcome.
6.1 Basic example
Suppose I ask my son who he wants to invite to his birthday party, and he replies, “Everybody.” Since this isn’t helpful, I give him a list of eight children I’d consider inviting and ask him to pick which ones he seriously wants to invite. From this list, he selects five children.
Later, I ask my wife why he chose those five. She explains that he invited everyone from his kindergarten group and older girls. As a scientist, I want to logically verify her explanation, so I collected the data shown in Table 6.1. The table lists all names, with binary values (“0” or “1”) indicating if a child is female, older, or in kindergarten (where “1” means true and “0” means false).
| Name | Female | Age | Kindergarten | Invited |
|---|---|---|---|---|
| Jürgen | 0 | 0 | 0 | 0 |
| Carl | 0 | 0 | 1 | 1 |
| Ben | 0 | 1 | 0 | 0 |
| Paul | 0 | 1 | 1 | 1 |
| Ida | 1 | 0 | 0 | 0 |
| Marie | 1 | 0 | 1 | 1 |
| Anna | 1 | 1 | 0 | 1 |
| Pia | 1 | 1 | 1 | 1 |