MR Dictionary

Regression dilution bias (attenuation by errors)

Refers to the expected attenuation towards the null of an association due to random measurement error in a risk factor. This is particularly likely to occur with risk factors that have naturally and widely fluctuating levels, such as blood pressure and (non-fasting) glucose. 

Because genetic variants instrument for lifetime (or long-term) levels of a risk factor, regression dilution bias is less likely in MR studies compared with other methods, such as multivariable regression, commonly used with observational data. 

References

Other terms in 'Sources of bias and limitations in MR':