maxdiff 3.0.2

Analysis library for MaxDiff (best-worst scaling) studies

maxdiff

Open tools for designing and analyzing MaxDiff (best-worst scaling) studies. The same analysis code ships in three forms: a zero-install browser tool hosted on GitHub Pages, a single-file Windows desktop EXE with optional Hierarchical Bayes, and a pip-installable Python package (pip install maxdiff) for use in scripts and notebooks. Uploaded data never leaves your machine in any of the three modes.

Quick start

Browser

No install. Open the tool in any modern browser; the Python analysis runs locally under Pyodide/WebAssembly and your data is never uploaded.

• Analysis tool: https://milkywaycj.github.io/maxdiff/analysis/ — count-based MaxDiff scores with optional bootstrap confidence intervals.
• Design tool: https://milkywaycj.github.io/maxdiff/design/ — balanced MaxDiff design generation.

Hierarchical Bayes is intentionally not offered in the browser tool; the JAX/NumPyro stack is too heavy for Pyodide.

Desktop (Windows)

Download the latest Windows EXE from the releases page. Hierarchical Bayes is bundled — no extra install needed.

First run on Windows. The EXE is not code-signed (this is a free open-source project and Microsoft does not offer a free signing option), so Windows SmartScreen will warn you twice: once during the download in your browser, and again when you launch the EXE. Both warnings are expected for unsigned open-source binaries and don't mean the EXE is unsafe — the source is in this repository and CI builds it from a tagged commit.

1. In the browser. Edge (and other Chromium-based browsers) show a "Make sure you trust ... before you open it" dialog in the Downloads panel with Cancel and Delete buttons. Click the small chevron next to Delete and choose Keep anyway. (If the dialog also offers Report this app as safe, that's optional — it just submits a reputation hint to Microsoft.)
2. At launch. Double-clicking the EXE produces a blue "Windows protected your PC" SmartScreen dialog. Click the small More info link, then the Run anyway button that appears.

SmartScreen remembers the decision after the first run. The EXE launches a customtkinter GUI; on launch it probes for jax / numpyro and enables the Hierarchical Bayes option if they are importable. The bundled EXE always has them. If you'd rather avoid the dialogs entirely, the pip install maxdiff path below works on any platform with Python and has no SmartScreen interaction.

Python package

pip install maxdiff             # core (pandas / numpy / matplotlib)
pip install maxdiff[hb]         # + jax + numpyro for Hierarchical Bayes
pip install maxdiff[desktop]    # + customtkinter / seaborn / openpyxl

A minimal end-to-end use of the count analysis:

import pandas as pd
from maxdiff import calculate_observed_percentages

df = pd.DataFrame({
    "Response ID":   [1, 1, 1, 2, 2, 2],
    "Attribute1":    ["A", "B", "C", "A", "B", "C"],
    "Attribute2":    ["B", "C", "A", "B", "C", "A"],
    "Attribute3":    ["C", "A", "B", "C", "A", "B"],
    "Best":          ["A", "B", "A", "B", "C", "A"],
    "Worst":         ["C", "A", "C", "A", "A", "B"],
})
scores = calculate_observed_percentages(
    df,
    attribute_columns=["Attribute1", "Attribute2", "Attribute3"],
    pos_col="Best",
    neg_col="Worst",
    output_terms=("Best", "Worst"),
)
print(scores)

The full public surface (count, bootstrap, display statistics, correlation, format detection, color parsing, encoding-aware file reads, plotting, and Hierarchical Bayes) is re-exported from the top-level maxdiff namespace; see docs/ARCHITECTURE.md for the per-module breakdown.

Features

• Count-based scoring. Per-item best-rate, worst-rate, percent- unselected, and net score, sorted. Research consistently shows this correlates r > 0.99 with Hierarchical Bayes utilities on standard balanced designs.
• Bootstrap confidence intervals. Respondent-level resampling (preserves within-respondent task clustering), reports the observed score together with the 2.5 / 97.5 percentile interval.
• Hierarchical Bayes (optional, requires jax + numpyro). NUTS sampling with a non-centered respondent parameterization and a hard sum-to-zero identification constraint so the prior is symmetric across items and extreme items aren't biased outward. R-hat thresholds follow Vehtari et al. 2021.
• Display statistics and balance metrics. Per-item display counts, selection counts, and study-level balance diagnostics.
• Segment analysis. Run the full pipeline within a categorical segmentation column.
• Correlation matrix. Item-item Pearson correlation derived from best/worst selection patterns.
• Design generation (browser tool). Balanced MaxDiff designs with uniform per-version slot randomization, downloadable as CSV.
• Format-tolerant I/O. Encoding fallbacks (UTF-8, UTF-8-sig, UTF-16, CP1252, Latin-1) for the messy CSVs that come out of Qualtrics / SurveyMonkey / Excel; format auto-detection for ready-to-analyze and Qualtrics-wide layouts.
• Thread-safe plotting. Matplotlib OO API only (no pyplot globals, no seaborn) so the GUI can render plots from a worker thread without corrupting state.

Project structure

maxdiff/
  src/
    maxdiff/                       Installable analysis package
      __init__.py                  Public API re-exports
      _version.py                  Single source of version truth
      count.py                     Count-based scoring
      bootstrap.py                 Bootstrap CIs (respondent-level)
      correlation.py               Item-item correlation matrix
      display.py                   Per-item stats and balance metrics
      formats.py                   Format detection, conversion, validation
      colors.py                    Hex / named color input parsing
      hb.py                        Hierarchical Bayes (optional jax/numpyro)
      io.py                        Encoding-aware tabular file reader
      plotting.py                  Thread-safe matplotlib (OO API) plots
    MaxDiff_Data_Analyzer_v2-1.py  customtkinter desktop GUI (imports maxdiff)

  docs/                            GitHub Pages site
    index.html                     Landing page
    analysis/index.html            Browser analysis tool (Pyodide + micropip)
    design/index.html              Browser design tool
    wheels/<version>/              In-repo wheel served to Pyodide
    vendor/pyodide-<version>/      Vendored Pyodide runtime (same-origin)
    RELEASE.md                     Release procedure
    ARCHITECTURE.md                Architecture and design notes

  scripts/
    vendor_pyodide.py              Re-runnable fetch of docs/vendor/pyodide-*

  tests/
    unit/                          Fast, isolated module tests
    property/                      Hypothesis property-based tests
    statistical/                   Monte Carlo recovery / coverage tests
    golden/                        Pinned-output regression tests
    e2e/                           Playwright browser-driven tests
    helpers/                       Synthetic data generator, loaders

  pyinstaller/                     Windows EXE build notes
  .github/workflows/               CI (Linux+Windows × Py 3.10-3.12), release
  pyproject.toml                   Build, deps, pytest, ruff, coverage config

Development

git clone https://github.com/milkywaycj/maxdiff
cd maxdiff
python -m venv .venv
. .venv/bin/activate              # PowerShell: .venv\Scripts\Activate.ps1
pip install -r requirements.txt -r requirements-dev.txt
pip install -e .                  # editable install of the maxdiff package

Optional extras:

pip install -r requirements-hb.txt          # JAX + NumPyro for HB tests
playwright install chromium                  # required for tests/e2e/

Run the suite:

pytest -q                          # full suite, ~1-2 min with HB + e2e
pytest -q -m "not slow"            # sub-minute fast tier
pytest tests/unit                  # one tier
pytest --cov                       # with coverage

Lint and format checks:

ruff check src/ tests/
ruff format --check src/ tests/

Browser end-to-end tests use Playwright + Chromium against a local http.server serving docs/; they're in tests/e2e/. They skip gracefully if Chromium isn't installed.

CI runs the matrix Linux + Windows × Python 3.10 / 3.11 / 3.12 on every push; HB-dependent tests are installed and run on Linux only because installing JAX on Windows runners is prohibitively slow and the HB code paths are platform-independent.

Releasing

See docs/RELEASE.md. The short version: bump src/maxdiff/_version.py, update CHANGELOG.md, push a v*.*.* tag; .github/workflows/release.yml builds the wheel, sdist, and HB-enabled Windows EXE and attaches them to a GitHub Release.

Contributing

Issues and PRs welcome at https://github.com/milkywaycj/maxdiff/issues. A few norms:

• Every behavior change ships with a test. Test-first (red → green → refactor) is the working norm here, not an aspiration. New numerical output gets a golden; new algorithmic behavior gets a statistical test; new validation paths get unit tests for each error branch. The test pyramid (unit / property / statistical / golden / integration / e2e) is described in docs/ARCHITECTURE.md.
• Commit messages are descriptive and self-contained — title summarizing the change in the imperative, body explaining the why, one logical change per commit. Phases of work get a Phase N: prefix when they belong to a multi-commit effort.
• Lint and format must pass (ruff check, ruff format --check).
• CI must be green on Linux and Windows across Python 3.10–3.12 before merge.
• For larger changes, open an issue first to agree on scope. Bug reports with a minimal reproducing dataset (even synthetic) are significantly easier to action than free-form descriptions.

License

MIT. See LICENSE.