als-statistics/lib/table/instruments/cronbach-alpha.js

A powerful and lightweight JavaScript library for descriptive statistics, regression, clustering, outlier detection, and noise analysis using a flexible table/column architecture.

class CronbachAlpha {
   static cronbachAlpha(table, obj = {}) {
      const { columnsN } = table;
      if (columnsN < 2) throw new Error("For Alpha Cronbach needs >=2 ratio columns.");
      obj.sumOfVariances = table.descriptive('varianceSample').sum;
      obj.sumColumnVariance = table.compute(row => Object.values(row).reduce((s, v) => s + v, 0)).varianceSample;
      obj.bessel = columnsN / (columnsN - 1);
      obj.alpha = obj.sumColumnVariance === 0 ? 0 : obj.bessel * (1 - obj.sumOfVariances / obj.sumColumnVariance);
      return obj;
   }

   constructor(table) {
      this.table = table;
      CronbachAlpha.cronbachAlpha(table, this);
   }

   get perColumn() { return this.ifItemsDeleted(); }

   ifItemsDeleted(columnFilter) {
      const result = {};
      for (let colName in this.table.columns) {
         const filter = columnFilter || ['-' + colName];
         result[colName] = CronbachAlpha.cronbachAlpha(this.table.clone(true, filter)).alpha;
      }
      return result;
   }
}

module.exports = CronbachAlpha;