I am trying to analyse the impact of experiencing a certain incident on the pro-unification opinion of people. If the incident occurs, they can occur in solely 3 different types: A, B and C. We assume that there is no other type of incident. So the general form of the regression is: 𝑜𝑝𝑖𝑛𝑖𝑜𝑛=𝛼+𝛽∗𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡+𝜖 Please note that I left out the subscripts for simplicity reasons.
I have troubles interpreting the coefficients starting from model (4). First, people who experienced incident of type A seem to have a significant effect (*, 10% level) on opinion compared to people with no incident or other types of incident. However, the effect of incident B (model 5) and C (model 6) are not significant at all. However, in model (6) the estimate for incident A is not significant, but for incident B and C. Further, model (8) also leads to a non-significant estimate of incident A. (Note: "Incident" is not the constant but also a dummy variabel for whether an incident occurred regardless of type of incident.)
How can I interpret the results? Is the result inconclusive? The R-Squareds are similar to each other, so one cannot choose between "better" models via R-Squared.