What this site does. You bring a table of numbers, it gives you
numbers back. This page gives every point a score - how far it lies from the
center of its column, counted in spreads - and flags the points whose score
passes a threshold. It runs entirely in your browser — nothing is uploaded,
nothing is stored. If you want the reasoning rather than the answer, the
outlier detection article explains
every method on a worked example.
A flag is a question, not a verdict: look at each flagged point before you
remove it. A long tail (response times, sizes, concentrations) is flagged by
every method here - take the logarithm first.
- Paste your data into the Input grid — straight from a
spreadsheet, or as CSV/TSV text — or import a CSV/TSV file.
Column t (time, or a row number), then up to three y columns. Up to 5,000
rows.
- Rows are sorted by t. A row with no number in t is skipped; a blank y cell is
skipped for that column only. Each column is judged on its own, and needs at
least 3 numbers.
- Pick a method.
- z-score: distance from the mean in standard
deviations. One large outlier can hide the others.
- modified z-score: distance from the median in MADs,
scaled like a z-score. Not fooled by the outliers themselves.
- IQR: distance beyond the middle half of the data, in
interquartile ranges - Tukey's fences, as on a box plot.
- Hampel: the modified z-score within a window of
neighbors around each point. For drifting signals.
- Set the threshold. Picking a method fills in its usual value:
3 for the z-score, 3.5 for the modified z-score, 1.5 for the IQR, 3 for
Hampel. A larger value flags fewer points.
- Set the window (Hampel only): the number of points on each
side, so the window holds 2 × window + 1 points. It must be longer than a
glitch and shorter than the changes in your signal.
- Real time range — try settings live on the threshold and
window boxes.
- ▲▼ buttons or the mouse wheel over a
box: the value moves and the result is recomputed at once - no need to
press detect.
- Digit wheel: over the threshold box, the wheel steps
the digit just left of the mouse pointer.
- Limits: threshold 0.1 to 20, window 1 to 50; a typed
value outside is set to the nearest limit.
- Typing or the arrow keys change the box only; press
detect to recompute.
- Press detect. The upper chart shows your data with the
threshold as dotted upper and lower lines in a lighter shade of each column's
color, in the data's own units: a point beyond them is an outlier. For Hampel the
lines follow the window. The lower chart shows each column's score against t,
with the outliers marked in a darker shade. The status line lists the flagged t
for each column that has any.
- Read the result. The Output grid lists t, then for each
column its score and a flag (1 = outlier, 0 = not). Export
saves it as a CSV/TSV file.