## 1.9 Descriptive vs. causal research questions

• Q: What is the difference?

### 1.9.1 Descriptive questions

• How are observations distributed across values of Y? (univariate)2
• e.g. How are individuals (observations) distributed across values of trust?

Table .: Univariate distribution of trust (2006)
0 1 2 3 4 5 6 7 8 9 10
303 42 172 270 369 1281 853 1344 1295 353 356

• How are observations distributed across values of Y and X?
• How are observations distributed across trust and gender values?
• We can add as many variables/dimensions as we like
• How are observations distributed across trust, gender and time values?
• Normally we summarize those distributions using models (associational inference)
• e.g. means of trust across gender across time

### 1.9.2 Causal questions

• Is there a causal link between the distribution across values of Y and values of D?
• Do differences in D cause differences in Y? (see app)
• Would individual i have another level trust (Y), had he not been victimized (D)?
• …in practice we tend to summarise those distributions..
• Continuous variables: Compare means
• Categorical variables (several): Compare probabilites for categories

Table .: Joint distribution of trust and victimization (2006, N = 6633)
0 1 2 3 4 5 6 7 8 9 10
no victim 259 36 135 214 320 1142 782 1228 1193 326 331
victim 44 6 37 56 48 139 70 114 101 27 25

* Q: How do I calculate the mean? * The mean of trust for non-victims is 6.2, the mean of trust for victims is 5.48.

1. See Gerring (2012) for a discussion of “What?” and “Why?” questions.