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Analysis

The Analysis tab explores a single record from several angles, including the frequency analysis that underpins return levels.

Analysis types

Pick a Type at the top of the control panel:

  • Time Series — the record, with optional resampling and a rolling-mean window.
  • Annual Maxima — the highest value per calendar year, with a trend.
  • Monthly Statistics — mean / median / max / sum by month, with optional ±1 std-dev bars.
  • Distribution Fit — fit one distribution and read its return levels.
  • Compare Distributions — fit Gumbel, GEV, Log-Normal and Pearson III and rank them by AIC (with KS statistics).
  • Outlier Analysis — flag extreme values without removing them.

Distribution Fit options

  • Distribution — Gumbel (EV1), GEV, Log-Normal, or Pearson III.
  • Estimation method — Maximum Likelihood (MLE), Method of Moments (MoM), or L-moments (Hosking). Shown for Gumbel, which has distinct closed-form estimators; other distributions use MLE.
  • View — PDF + Return Period or CDF.
  • Show empirical points — Weibull plotting positions overlaid on the curve.
  • Show 95% confidence band — a parametric bootstrap (with a Bootstrap samples count); slower for GEV and Pearson III.
  • Compare all distributions — jumps straight to the ranked comparison.

Screening (applies to every analysis on this tab)

  • Completeness screening — exclude calendar years below a completeness threshold; Review flagged years… lets you keep specific ones.
  • Exclude outliers — IQR, Log Z-score, Modified Z (MAD), and Grubbs, with per-method thresholds and a per-point review. (Hidden for Outlier Analysis, which must keep its outliers.)

Both are off by default and screen independently of the IDF and Diagnostics tabs. Compare impact… renders the current analysis with and without the active screening, side by side, listing exactly what changed.

Every distribution, estimator, and screening rule here — each with its source — is summarised in the Methods overview.

Results

Run from ▶ Run Analysis (heavy fits can be Cancelled mid-run). The plot has its own toolbar and a Pop out button for report sizing; report-ready output appears in the Analysis Results panel below.

See also: IDF Curves · Methods & References