WIP: Abstract type for summary statistics (Mean)

src/SummaryStats.jl

@@ -0,0 +1,71 @@
+"""
+    SummaryStats
+
+Supertype for every type of summary statistic. 
+
+"""
+
+abstract type SummaryStats end
+
+"""
+    Calculate confidence intervals for given estimates.
+
+"""
+
+function confint(estimate::Float64, std_dev::Float64; type::String="normal", alpha::Float64=0.05)
+    # Parse type of CI & calculate critical value
+    if type == "normal"
+        critical_value = quantile(Normal(), 1 - alpha / 2)
+    end
+    # Calculate upper and lower estimates
+    lower = estimate .- critical_value .* std_dev
+    upper = estimate .+ critical_value .* std_dev
+    return (lower=lower, upper=upper)
+end
+
+"""
+
+    Mean <: SummaryStats
+
+Population mean estimate for a column of a SurveyDesign object.
+
+# Arguments:
+- `x::Symbol`: the column to compute population mean statistics for.
+- `design::SurveyDesign`: a SurveyDesign object.
+
+```jldoctest
+julia> using Survey;
+julia> apiclus1 = load_data("apiclus1");
+julia> dclus1 = SurveyDesign(apiclus1; clusters=:dnum, strata=:stype, weights=:pw);
+
+julia> api00_mean = Mean(:api00, dclus1)
+(x = :api00, estimate = 644.1693989071047, std_dev = 105.74886663549471)
+
+julia> api00_mean.estimate
+644.1693989071047
+
+julia> api00_mean.std_dev
+105.74886663549471
+
+julia> api00_mean.CI
+(lower = 436.90542889560527, upper = 851.4333689186041)
+
+```
+
+# TODO add :
+#std_err = stderror(design, x)              # standard error of the estimate of the mean
+
+"""
+
+struct Mean <: SummaryStats
+    x::Symbol
+    design::SurveyDesign
+end
+
+function Mean(x::Symbol, design::SurveyDesign)
+    column = design.data[!, x]
+    estimate = mean(column, weights(design.data[!, design.weights]))
+    std_dev = std(column)
+    CI = confint(estimate, std_dev)
+    return (x=column, estimate=estimate, std_dev=std_dev, CI=CI)
+end