Formula
Geometric adstock: A(t) = x(t) + θ × A(t-1)
Why it matters
For adstock it equals ln(0.5) divided by ln(θ), so a carryover of 0.6 gives about 1.4 weeks. Longer half-lives mean a campaign should be judged across several weeks.
Glossary // H / Pharmacokinetics
What is Half-life?
Definition
Half-life is the time it takes for an effect to fall to half its starting size.