Funnel plot and Egger's test for epidemiological studies on ionizing radiation and dementia. Relative risk in the funnel plot above represents the ratio of the risk of dementia incidence or mortality in populations exposed to over 100 mSv of radiation compared to the risk in those exposed to lower doses of doses. The funnel plot shows slight asymmetry and thus may imply the presence of publication bias. This was tested using the Egger's test that produced no statistically significant evidence of publication bias with P = 0.781.