I want to know what ranges of value can D' in linkage disequilibrium take? Because I read in my book (An introduction to population genetics by Nielsen and Slatkin) that D' is guaranteed to be between 0 and 1. Whereas at the link provided below, it says D' can be between -1 and 1.
http://csg.sph.umich.edu/abecasis/class/666.03.pdf
Could someone explain this discrepancy? Because now I am totally confused.
The whole point about using D' rather than D is because D' is bounded between -1 an 1 for any allele frequency, while the bounds for D depends upon the allele frequency of interest.
Recall the definition of D
$$D = p_{ab} - p_ap_b$$
Let, $D_{min}$ and $D_{max}$ be the minimal and maximal values of $D$ for a specific allele frequency.
For $p_a = p_b = 0.5$, the $D_min$ is when when $p_{ab} = 0$ ($D_{min} = -0.25$) and $D_{max}$ is when $p_{ab} = 1$ ($D_{max}=0.75$).
For $p_a = 0.8$ and $p_b = 0.2$, the $D_min$ is when when $p_{ab} = 0$ ($D_{min} = -0.16$) and $D_{max}$ is when $p_{ab} = 0.2$ ($D_{max}=0.04$).
