Interpreting Johansen Cointegration Eigenvectors Versus OLS Coefficients
Summary
The document asks why a cointegrating vector from a Johansen test differs from coefficients estimated by ordinary least squares in a model of firm revenues and several explanatory variables. The reported test statistics are interpreted as indicating one cointegrating relation, and the question compares the associated normalized eigenvector with OLS estimates from a proposed two-stage equation.
It provides the model equations, test output, and coefficient values, but no answer explaining the discrepancy. In particular, it does not establish that the Johansen vector should match the OLS regression coefficients. The material is therefore a useful question about interpreting cointegration output, rather than a worked explanation. It leaves unresolved the effects of normalization, system estimation, deterministic terms, model specification, and the choice of variables on the comparison.
Key ideas
- The question concerns a Johansen cointegrating vector and OLS coefficients in a firm-revenue model.
- The reported test output is interpreted as supporting one cointegrating relation.
- The eigenvector and OLS estimates differ, but the document gives no explanation for why.
- Normalization and model specification are unresolved issues in the comparison.
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Full text
# Understanding output from Johansen Cointegration test
# Understanding output from Johansen Cointegration test
I have a VECM model that Im using to determine the revenues for a firm, based on factors like Interest rates, S&P 500 and company specific variables, as follows:
Stage 1: $$z_t= a+ bX_t+e_t$$
Stage 2: $$ \Delta z_t = \alpha_1 (z_{t-1}-a-bX_{t-1}) + \gamma_{11} \Delta z_{t-1} + \gamma_{12} \Delta X_{t-1} +\varepsilon_{t} $$
where t is in months and $z_t$ are Firm revenues
After running a Johansen Cointegration Test in R I get the following result.
```
test 10pct 5pct 1pct
r <= 3 | 1.26 7.52 9.24 12.97
r <= 2 | 9.15 11.41 15.53 23.21
r <= 1 | 20.07 19.37 21.10 23.71
r = 0 | 47.23 22.32 25.23 36.33
```
Based on this there is only one linear combination that results in a stationary series.
The eigenvector associated with the highest eigenvalue, based on the output in R, "Eigenvectors, normalised to first column: (These are the cointegration relations)" is:
```
1.0000
-0.732
0.6174
-5.123
6.1542
```
The value in the first row is just the value associated with Z.
Based on this answer, which says that the linear combination of the eigenvector associated with the highest eigenvalue will result in a stationary series, I was assuming this vector would be the same as the coefficients I estimated via OLS. However, this doesn't seem to be the case and I was just wondering why this might be.
Coefficients from OLS:
```
0.729905
−0.048841
4.224540
−6.281800
```
Comparing the 2nd to 5th rows of the eigenvector from the Johansen test to the coefficients from the OLS it can be seen that the magnitudes are fairly close but the 2nd row is quite far off (the signs would be the same by taking into account the fact that the eigenvector would be on the other side of the equation for the eigenvector combination). Is there a reason for this difference?
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This summary was written by Stratmill's research agent from the original; it is not a copy of the source.