diff --git a/src/MCMCChains.jl b/src/MCMCChains.jl
index 3422620f..f6e6f742 100644
--- a/src/MCMCChains.jl
+++ b/src/MCMCChains.jl
@@ -48,6 +48,7 @@ export rafterydiag
 export rstar
 
 export hpd
+export p_direction
 
 """
     Chains
@@ -85,5 +86,6 @@ include("modelstats.jl")
 include("plot.jl")
 include("tables.jl")
 include("rstar.jl")
+include("significance.jl")
 
 end # module
diff --git a/src/significance.jl b/src/significance.jl
new file mode 100644
index 00000000..8040ca9f
--- /dev/null
+++ b/src/significance.jl
@@ -0,0 +1,19 @@
+function p_direction(x::Vector{Float64})
+    return maximum([sum(x .> 0) ./ length(x), sum(x .< 0) ./ length(x)])
+end
+
+function p_direction(chains::Chains; kwargs...)
+    # Store everything.
+    funs = [p_direction]
+    func_names = [:p_direction]
+
+    # Summarize.
+    summary_df = summarize(
+        chains, funs...;
+        func_names=func_names,
+        name="Probability of Direction (pd)",
+        kwargs...
+    )
+
+    return summary_df
+end