als-statistics/lib/analyze/correlate/cronbach-alpha.js

Modular JS statistics toolkit for Node.js and the browser: descriptive stats, correlations (Pearson/Spearman/Kendall), t-tests & ANOVA (Student/Welch), reliability (Cronbach’s alpha), regression (linear/logistic), clustering (DBSCAN/HDBSCAN), and table/co

import { htmlTable } from '../../utils/html-table.js';
import { TestBase, stats } from '../test-base/index.js';

export class CronbachAlpha extends TestBase {
   #ifItemsDeleted
   constructor(samples) {
      super(samples, 'Cronbach Alpha', ['alpha'], { sameSize: true, minK: 2 });
      this.sumOfVariances = this.samples.reduce((t, { varianceSample }) => t + varianceSample, 0)
      const transposed = Array.from({ length: this.n }, (_, i) => Array.from({length:this.k},(_,j) => this.samples[j].values[i]))
      this.sumColumnVariance = stats(transposed.map(arr => arr.reduce((t,v) => t+v,0))).varianceSample
      this.bessel = this.k / (this.k - 1);
      this.alpha = this.sumColumnVariance === 0 ? 0 : this.bessel * (1 - this.sumOfVariances / this.sumColumnVariance);
   }

   get ifItemsDeleted() {
      if (this.#ifItemsDeleted) return this.#ifItemsDeleted
      this.#ifItemsDeleted = {};
      this.samples.forEach(col => {
         const cols = {}
         this.samples.forEach((s) => {
            if (s.name !== col.name) cols[s.name] = s
         })
         this.#ifItemsDeleted[col.name] = new CronbachAlpha(cols).alpha;
      })
      return this.#ifItemsDeleted;
   }

   get htmlTable() {
      const { alpha, ifItemsDeleted } = this
      return /*html*/`
      <h2>Cronbach Alpha</h2>
      <hr>
      Alpha: ${alpha}
      <br><br>
      ${htmlTable(Object.entries(ifItemsDeleted),['variable','alpha if deleted'])}
      `
   }
}