I am looking for the proper term for a regression/correlation that is artificially inflated due to the two variables being related by a common factor. I'm a biologist trying to determine if birth intervals increase with age. I initially fitted a regression between the birth interval and the age at the end of the birth interval, but I think that approach is biased and artificially introduces a positive relationship. Age at the end of the birth interval is equal to the age at the beginning of the interval plus the birth interval. The birth interval is thus a component of both the dependent and independent variables. Even if there is no relationship between age and birth interval, and birth intervals are random, I would get a positive relationship because animals tend to be older at the end of long birth intervals. If I regress the birth interval on age at the beginning of the birth interval, I can eliminate this bias. I recall there being a term for such a biased regression, but can't remember what it is.