Hypermorbidity in respiratory symptoms among smokers in the population sample is in good agreement with other reports. The fact that this hypermorbidity was found also among smokers in smoking-discordant monozygotic twin pairs by use of the twin-control method speaks in favor of a causal interpretation. The hypermorbidity in "angina pectoris" among smokers in the population sample of firstborn twins is of the same order of magnitude as in other reports in regard to hypermortality—hypermorbidity investigations being sparse and not unanimous.
Source: wiktionary