Table 2.

Methodological difficulties and factors decreasing apparent rupture risks in ISUIA.

1. Poorly defined objectives and indeterminate hypotheses
2. Irrelevant population of patients excluded from treatment
3. Selection bias at entry manifest by:	a. age
(all p <.001 as compared to treated cohorts)	b. Size of lesion
	c. History of hemorrhage from another lesion
	d. Location
	e. Multiplicity
	f. Symptoms
4. Undefined observation period
5. Error rates and sample size not pre-specified
6. Excessive losses to follow-up (21% of patients	a. Excessive loss by unrelated (?)
followed at 4 years)	mortality (12.7%)
	b. Excessive loss by cross-over
	(32% eventually treated; reasons?)
7. Assessment of outcome events was not blind
8. Exclusion of events when other potential causes for intracranial bleeding (n=31)
9. Exclusion of other intracranial hemorrhagic deaths (n= 19)
10. Exclusion of deaths of unknown cause (n= 11)
11. Post-hoc definition of subgroups
12. Arbitrary relocation of P. Com aneurysms
13. Inclusion of extradural lesions (cavernous lesions)
14. Systematic attribution to large or posterior location categories when lesions multiple (40%)
15. Incomplete reporting:	a. Actual numbers not provided
	b. Confidence intervals not provided
	c. Methodological obscurities