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.↩