From eb2db429c3900ba85144aa94497a97844c607337 Mon Sep 17 00:00:00 2001
From: Dirk Schumacher <mail@dirk-schumacher.net>
Date: Fri, 1 Nov 2024 12:01:05 +0100
Subject: [PATCH] Fix overflow in zscore estimates

---
 R/prevalence-simple.R                             | 4 ++--
 tests/testthat/test-prevalence-simple-estimates.R | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/R/prevalence-simple.R b/R/prevalence-simple.R
index ee12c0e..b97b323 100644
--- a/R/prevalence-simple.R
+++ b/R/prevalence-simple.R
@@ -162,7 +162,7 @@ sample_size <- function(x, N, empty_data_prototype) {
 }
 
 sample_se <- function(x, x_mean, n, N) {
-  scale <- N / (N - 1) * 1 / (n * n)
+  scale <- N / (N - 1)
   x_deviation <- x - x_mean
-  sqrt(sum(scale * x_deviation * x_deviation))
+  sqrt(scale)/n * sqrt(sum(x_deviation * x_deviation))
 }
diff --git a/tests/testthat/test-prevalence-simple-estimates.R b/tests/testthat/test-prevalence-simple-estimates.R
index 164c220..248b2b2 100644
--- a/tests/testthat/test-prevalence-simple-estimates.R
+++ b/tests/testthat/test-prevalence-simple-estimates.R
@@ -30,3 +30,10 @@ test_that("survey and approximation yield are equal within tolerance", {
     expect_equal(res_simple[[!!col]], res_survey[[!!col]], tolerance = 0.0001)
   }
 })
+
+test_that("zscore estimates should not overflow", {
+  x <- rnorm(100000)
+  expect_no_warning(
+    zscore_estimate(x, length(x), data.frame())
+  )
+})