diff --git a/.github/workflows/package.yml b/.github/workflows/package.yml
new file mode 100644
index 0000000..349bbaf
--- /dev/null
+++ b/.github/workflows/package.yml
@@ -0,0 +1,68 @@
+name: CI
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: True
+      matrix:
+        python-version: [ "3.11" ]
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v3
+      - name: Set up python
+        id: setup-python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.11'
+
+      - name: Install Poetry
+        uses: snok/install-poetry@v1
+        with:
+          virtualenvs-create: true
+          virtualenvs-in-project: true
+          installer-parallel: true
+
+      - name: Load cached venv
+        id: cached-poetry-dependencies
+        uses: actions/cache@v3
+        with:
+          path: .venv
+          key: venv-${{ runner.os }}-${{ steps.setup-python.outputs.python-version }}-${{ hashFiles('**/poetry.lock') }}
+
+      - name: Install dependencies
+        if: steps.cached-poetry-dependencies.outputs.cache-hit != 'true'
+        run: poetry install --no-interaction --no-root
+
+      - name: Activate env
+        run: |
+          source .venv/bin/activate
+
+      - uses: chartboost/ruff-action@v1
+        name: Ruff
+        with:
+          args: --check .
+          config: pyproject.toml
+
+      - name: Run mypy
+        run: |
+          mypy .
+
+      - name: Run tests
+        run: |
+          pytest --cov tests/
+
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v4-beta
+        with:
+          flags: smart-tests
+          verbose: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
\ No newline at end of file
diff --git a/src/obscure_stats/association/association.py b/src/obscure_stats/association/association.py
index 9ed0b4c..38ccb89 100644
--- a/src/obscure_stats/association/association.py
+++ b/src/obscure_stats/association/association.py
@@ -154,9 +154,9 @@ def concordance_rate(
     It could be seen as simplified version of Pearson's R.
 
     It differs from quadrant count ratio by adding and exclusion zone
-    variation has an option for an exclusion zone.
-    It is based on the standard error of the mean and will exlucde
-    points that are in the range of mean+-sem.
+    variation has an option for an exclusion zone. It is based on the
+    standard error of the mean and will exlucde points that are in the
+    range of mean+-sem.
 
     Parameters
     ----------
diff --git a/src/obscure_stats/dispersion/__init__.py b/src/obscure_stats/dispersion/__init__.py
index d648e0e..62b0710 100644
--- a/src/obscure_stats/dispersion/__init__.py
+++ b/src/obscure_stats/dispersion/__init__.py
@@ -4,7 +4,6 @@
     coefficient_of_lvariation,
     coefficient_of_variation,
     dispersion_ratio,
-    efficiency,
     lloyds_index,
     morisita_index,
     quartile_coefficient_of_dispersion,
@@ -17,7 +16,6 @@
     "coefficient_of_lvariation",
     "coefficient_of_variation",
     "dispersion_ratio",
-    "efficiency",
     "lloyds_index",
     "morisita_index",
     "quartile_coefficient_of_dispersion",
diff --git a/src/obscure_stats/dispersion/dispersion.py b/src/obscure_stats/dispersion/dispersion.py
index 1ca430a..d21bbc8 100644
--- a/src/obscure_stats/dispersion/dispersion.py
+++ b/src/obscure_stats/dispersion/dispersion.py
@@ -8,31 +8,6 @@
 EPS = 1e-6
 
 
-def efficiency(x: np.ndarray) -> float:
-    """Calculate array efficiency (squared CV).
-
-    Parameters
-    ----------
-    x : array_like
-        Input array.
-
-    Returns
-    -------
-    eff : float or array_like.
-        The value of the efficiency.
-
-    References
-    ----------
-    Grubbs, F. E. (1965).
-    Statistical Measures of Accuracy for Riflemen and Missile Engineers. pp. 26-27.
-    """
-    mean = np.nanmean(x)
-    if abs(mean) <= EPS:
-        warnings.warn("Mean is close to 0. Statistic is undefined.", stacklevel=2)
-        return np.inf
-    return np.nanvar(x) / mean**2
-
-
 def studentized_range(x: np.ndarray) -> float:
     """Calculate range normalized by standard deviation.
 
@@ -59,7 +34,10 @@ def studentized_range(x: np.ndarray) -> float:
 
 
 def coefficient_of_lvariation(x: np.ndarray) -> float:
-    """Calculate linear coefficient of variation (MeanAbsDev / Mean).
+    """Calculate linear coefficient of variation.
+
+    L-CV is the L-scale (half of mean absolute deviation) divided
+    by L-mean (the same as regular mean).
 
     Parameters
     ----------
@@ -87,7 +65,7 @@ def coefficient_of_lvariation(x: np.ndarray) -> float:
 
 
 def coefficient_of_variation(x: np.ndarray) -> float:
-    """Calculate coefficient of variation (Std / Mean).
+    """Calculate coefficient of variation (Standard deviation / Mean).
 
     Parameters
     ----------
@@ -115,7 +93,8 @@ def coefficient_of_variation(x: np.ndarray) -> float:
 def robust_coefficient_of_variation(x: np.ndarray) -> float:
     """Calculate robust coefficient of variation.
 
-    It is based on median absolute deviation from the median (MedAbsDev / Median).
+    It is based on median absolute deviation from the median, i.e. median
+    absolute deviation from the median divided by the median.
 
     Parameters
     ----------
@@ -170,6 +149,11 @@ def quartile_coefficient_of_dispersion(x: np.ndarray) -> float:
 def dispersion_ratio(x: np.ndarray) -> float:
     """Calculate dispersion ratio (Mean / GMean).
 
+    The closer a dispersion ratio is to 1, the lower the dispersion
+    between the observations within an array.
+    In this function geometric mean computed by excluding zeros and
+    missing data points.
+
     Parameters
     ----------
     x : array_like
@@ -187,7 +171,9 @@ def dispersion_ratio(x: np.ndarray) -> float:
     prior to unsupervised machine learning.
     Statistics, Optimization & Information Computing, 11(2), 519-530.
     """
-    return np.nanmean(x) / (stats.gmean(x, nan_policy="omit") + EPS)
+    _x = np.asarray(x)
+    _x = np.where(_x == 0, np.nan, _x)
+    return np.nanmean(x) / stats.gmean(_x, nan_policy="omit")
 
 
 def lloyds_index(x: np.ndarray) -> float:
@@ -246,8 +232,8 @@ def morisita_index(x: np.ndarray) -> float:
 def sqad(x: np.ndarray) -> float:
     """Calculate Standard quantile absolute deviation.
 
-    This measure is a robust measure of dispersion, that does not need
-    normalizing constant like MAD and has higher gaussian efficiency.
+    This measure is a robust measure of dispersion, that has higher
+    gaussian efficiency, but lower breaking point.
 
     Parameters
     ----------
@@ -266,5 +252,8 @@ def sqad(x: np.ndarray) -> float:
     arXiv preprint arXiv:2208.13459.
     """
     med = np.nanmedian(x)
-    # constant value to maximize efficiency for normal distribution
-    return np.nanquantile(np.abs(x - med), q=0.682689492137086)
+    n = len(x)
+    # finite sample correction
+    k = 1.0 + 0.762 / n + 0.967 / n**2
+    # constant value that maximizes efficiency for normal distribution
+    return k * np.nanquantile(np.abs(x - med), q=0.682689492137086)
diff --git a/src/obscure_stats/kurtosis/kurtosis.py b/src/obscure_stats/kurtosis/kurtosis.py
index 045c565..3e5d423 100644
--- a/src/obscure_stats/kurtosis/kurtosis.py
+++ b/src/obscure_stats/kurtosis/kurtosis.py
@@ -8,6 +8,11 @@
 def moors_kurt(x: np.ndarray) -> float:
     """Calculate Moor's vision of kurtosis, based on Z score.
 
+    The kurtosis can now be seen as a measure of the dispersion of
+    squared Z around its expectation.
+    Alternatively it can be seen to be a measure of the dispersion
+    of Z around +1 and -1.
+
     Parameters
     ----------
     x : array_like
diff --git a/src/obscure_stats/skewness/skewness.py b/src/obscure_stats/skewness/skewness.py
index a6c1000..6e56e6a 100644
--- a/src/obscure_stats/skewness/skewness.py
+++ b/src/obscure_stats/skewness/skewness.py
@@ -138,7 +138,9 @@ def medeen_skew(x: np.ndarray) -> float:
 def bowley_skew(x: np.ndarray) -> float:
     """Calculate Bowley's skewness coefficinet.
 
-    It is based on quartiles (uncentered, unscaled).
+    Also known as Yule-Kendall skewness coefficient.
+    It is based on quartiles (uncentered, unscaled) and compares the distance
+    between the median and each of the two quartiles.
     This measure should be more robust than moment based skewness.
 
     Parameters
diff --git a/tests/test_dispersion.py b/tests/test_dispersion.py
index 497d019..21a763a 100644
--- a/tests/test_dispersion.py
+++ b/tests/test_dispersion.py
@@ -8,7 +8,6 @@
     coefficient_of_lvariation,
     coefficient_of_variation,
     dispersion_ratio,
-    efficiency,
     lloyds_index,
     morisita_index,
     quartile_coefficient_of_dispersion,
@@ -25,7 +24,6 @@
         coefficient_of_variation,
         robust_coefficient_of_variation,
         dispersion_ratio,
-        efficiency,
         lloyds_index,
         morisita_index,
         quartile_coefficient_of_dispersion,
@@ -54,7 +52,6 @@ def test_mock_aggregation_functions(
         coefficient_of_variation,
         robust_coefficient_of_variation,
         dispersion_ratio,
-        efficiency,
         lloyds_index,
         morisita_index,
         quartile_coefficient_of_dispersion,
@@ -79,7 +76,6 @@ def test_dispersion_sensibility(func: typing.Callable, seed: int) -> None:
         coefficient_of_variation,
         robust_coefficient_of_variation,
         quartile_coefficient_of_dispersion,
-        efficiency,
     ],
 )
 def test_cv_corner_cases(func: typing.Callable) -> None:
@@ -98,7 +94,6 @@ def test_cv_corner_cases(func: typing.Callable) -> None:
         coefficient_of_variation,
         robust_coefficient_of_variation,
         dispersion_ratio,
-        efficiency,
         lloyds_index,
         morisita_index,
         quartile_coefficient_of_dispersion,