binspect

Binned scatterplots for linear specification diagnostics.

binspect estimates binned conditional means and compares them with a linear fit to the underlying observations. The bin means are the fitted values from the saturated model OLS(y ~ C(bin)). Their weighted deviations from the line provide a descriptive linear specification diagnostic.

import binspect

bs = binspect.binscatter(df, y="sales", x="age", bins=20)

bs.table  # per-bin means, SDs, standard errors, intervals
bs.summary_frame()  # one-row model and diagnostic table
bs.to_dict()  # JSON-compatible structured results
print(bs.summary())
bs.plot(theme="paper")
bs.audit(theme="paper")  # plot plus marginal distributions and residuals

Adjust both variables for numeric or categorical controls with FWL residualization:

adjusted = binspect.binscatter(
    df,
    y="sales",
    x="age",
    controls=["region", "tenure"],
    bins=20,
)
adjusted.fit.slope  # age coefficient from OLS(sales ~ age + region + tenure)
adjusted.plot()  # axes are explicitly labelled as adjusted

Residualized variables retain their original means, keeping the plot on a familiar scale. Categorical controls are indicator-encoded and a constant is included automatically. With weights=, the projection uses the same reliability weights.

For comparisons across groups, pooled bin edges are used by default so facets refer to the same intervals of x:

comparison = binspect.compare(
    df,
    y="sales",
    x="age",
    group="region",
    bins=20,
)

comparison.table  # one row per group and bin
comparison.summary_frame()  # one row per group
comparison.plot(sharex=True, sharey=True)

Pass common_bins=False to select bins separately within each group. The pooled estimate remains available as comparison.pooled.

Related packages

binsreg (Cattaneo, Crump, Farrell, and Feng) provides formal binscatter inference. binspect delegates optimal bin selection to it when requested. Use binsreg when uniform confidence bands or formal shape-restriction tests are required.

What it draws

The default plot presents the estimates, uncertainty, linear fit, lack of fit, and distribution of the exogenous variable as separate layers.

Three themes are included: notebook (default), paper (thin, serif, grayscale-safe), and deck (larger marks and type). Themes are colorblind-safe and scoped; importing binspect does not modify global rcParams.

Use bs.audit() for a composed diagnostic figure with the unchanged binscatter in the central panel, marginal histograms, and OLS residuals against fitted values. Either companion view can be omitted with marginals=False or residuals=False. These panels describe the stored estimate; they do not add a formal specification test.

One thing to know about η²

The bin-indicator model does not nest the linear model. Consequently, η² can be below the linear R² when bins are coarse, and their difference is not a valid curvature measure. binspect reports normalized lack of fit,

SS_lof = Σⱼ nⱼ (ȳⱼ − ŷ(x̄ⱼ))²      gap = SS_lof / SS_total

which is nonnegative by construction and corresponds to the deviations shown in the plot. This quantity is descriptive and is not a formal test of linearity.

Status

Initial alpha release (0.1.0). The API may continue to evolve during the 0.x series. The distribution name is binspect-regression; the import remains binspect.

Not yet implemented: cluster-robust standard errors, uniform confidence bands, and quantile regression. Standard errors are currently sd/√n within bin and assume independent observations.

Install

git clone https://github.com/joshuamyers22/binspect.git && cd binspect
pip install -e ".[dev]"
pytest

Install the published package with pip install binspect-regression and continue to write import binspect.

For contributing, release checks, and development conventions, see CONTRIBUTING.md. Please report vulnerabilities privately as described in SECURITY.md.

Maintainer release instructions are in RELEASING.md.

License

MIT.

Citation

The methodology this package leans on is Cattaneo, M. D., Crump, R. K., Farrell, M. H., & Feng, Y. (2024). "On Binscatter." American Economic Review, 114(5), 1488–1514. If you use binned scatterplots for inference, cite that paper and consider using binsreg directly.