4 Replies Latest reply on Aug 31, 2016 10:50 AM by Sam Cheadle

    Comparison of test statistic with critical value (chi squared test)

    Sam Cheadle

      Hello,

       

      I am aiming to carry out a chi-squared test within Tableau (without using the R link up), and have followed this useful method....

      https://community.tableau.com/thread/117619

       

      However, this method stops short of providing a test result. Once the test statistic has been calculated (chi-squared value in my case), this needs to be compared with a critical value, determining whether the result is statistical significant or not. This critical value is dependent on the degrees of freedom or DF (for chi squared, related to the number of rows and columns of the test data).

       

      Is it possible to link to a separate data-source containing the critical values for a range of DFs (linked based on the DF value)? Testing this so far has failed, I believe because the DF value is a measure (calculated field), rather than a dimension.

       

      I think the only other option is to calculate the critical value directly, based on the chi-squared distribution. However, a factorial function is necessary for this, which is not currently available in Tableau.

       

      Many thanks,

      Sam

        • 1. Re: Comparison of test statistic with critical value (chi squared test)
          Benjamin Greene

          Your first idea (linking the separate data source) would be the way I would go. You can just right click the DF field and convert it to a dimension to use it as a linking field.

           

          The other (more laborious) option would be to create a calculated field like

           

          IF [DF]=5 THEN X critical value

          ELSEIF [DF]=6 THEN Y critical value

          ELSEIF [DF]=7 THEN Z critical value

          .

          .

          .

          etc.
          END

          • 2. Re: Comparison of test statistic with critical value (chi squared test)
            chris.moore.11

            I kind of like your second suggestion. Copying a table into excel and concatenating some text takes about 30 seconds.

             

            Example for p=.1

             

            if [DF] = 1 then 2.706

            elseif [DF] = 2 then 4.605

            elseif [DF] = 3 then 6.251

            elseif [DF] = 4 then 7.779

            elseif [DF] = 5 then 9.236

            elseif [DF] = 6 then 10.645

            elseif [DF] = 7 then 12.017

            elseif [DF] = 8 then 13.362

            elseif [DF] = 9 then 14.684

            elseif [DF] = 10 then 15.987

            elseif [DF] = 11 then 17.275

            elseif [DF] = 12 then 18.549

            elseif [DF] = 13 then 19.812

            elseif [DF] = 14 then 21.064

            elseif [DF] = 15 then 22.307

            elseif [DF] = 16 then 23.542

            elseif [DF] = 17 then 24.769

            elseif [DF] = 18 then 25.989

            elseif [DF] = 19 then 27.204

            elseif [DF] = 20 then 28.412

            elseif [DF] = 21 then 29.615

            elseif [DF] = 22 then 30.813

            elseif [DF] = 23 then 32.007

            elseif [DF] = 24 then 33.196

            elseif [DF] = 25 then 34.382

            elseif [DF] = 26 then 35.563

            elseif [DF] = 27 then 36.741

            elseif [DF] = 28 then 37.916

            elseif [DF] = 29 then 39.087

            elseif [DF] = 30 then 40.256

            elseif [DF] = 31 then 41.422

            elseif [DF] = 32 then 42.585

            elseif [DF] = 33 then 43.745

            elseif [DF] = 34 then 44.903

            elseif [DF] = 35 then 46.059

            elseif [DF] = 36 then 47.212

            elseif [DF] = 37 then 48.363

            elseif [DF] = 38 then 49.513

            elseif [DF] = 39 then 50.66

            elseif [DF] = 40 then 51.805

            elseif [DF] = 41 then 52.949

            elseif [DF] = 42 then 54.09

            elseif [DF] = 43 then 55.23

            elseif [DF] = 44 then 56.369

            elseif [DF] = 45 then 57.505

            elseif [DF] = 46 then 58.641

            elseif [DF] = 47 then 59.774

            elseif [DF] = 48 then 60.907

            elseif [DF] = 49 then 62.038

            elseif [DF] = 50 then 63.167

            elseif [DF] = 51 then 64.295

            elseif [DF] = 52 then 65.422

            elseif [DF] = 53 then 66.548

            elseif [DF] = 54 then 67.673

            elseif [DF] = 55 then 68.796

            elseif [DF] = 56 then 69.919

            elseif [DF] = 57 then 71.04

            elseif [DF] = 58 then 72.16

            elseif [DF] = 59 then 73.279

            elseif [DF] = 60 then 74.397

            elseif [DF] = 61 then 75.514

            elseif [DF] = 62 then 76.63

            elseif [DF] = 63 then 77.745

            elseif [DF] = 64 then 78.86

            elseif [DF] = 65 then 79.973

            elseif [DF] = 66 then 81.085

            elseif [DF] = 67 then 82.197

            elseif [DF] = 68 then 83.308

            elseif [DF] = 69 then 84.418

            elseif [DF] = 70 then 85.527

            elseif [DF] = 71 then 86.635

            elseif [DF] = 72 then 87.743

            elseif [DF] = 73 then 88.85

            elseif [DF] = 74 then 89.956

            elseif [DF] = 75 then 91.061

            elseif [DF] = 76 then 92.166

            elseif [DF] = 77 then 93.27

            elseif [DF] = 78 then 94.374

            elseif [DF] = 79 then 95.476

            elseif [DF] = 80 then 96.578

            elseif [DF] = 81 then 97.68

            elseif [DF] = 82 then 98.78

            elseif [DF] = 83 then 99.88

            elseif [DF] = 84 then 100.98

            elseif [DF] = 85 then 102.079

            elseif [DF] = 86 then 103.177

            elseif [DF] = 87 then 104.275

            elseif [DF] = 88 then 105.372

            elseif [DF] = 89 then 106.469

            elseif [DF] = 90 then 107.565

            elseif [DF] = 91 then 108.661

            elseif [DF] = 92 then 109.756

            elseif [DF] = 93 then 110.85

            elseif [DF] = 94 then 111.944

            elseif [DF] = 95 then 113.038

            elseif [DF] = 96 then 114.131

            elseif [DF] = 97 then 115.223

            elseif [DF] = 98 then 116.315

            elseif [DF] = 99 then 117.407

            elseif [DF] = 100 then 118.498

            elseif [DF] = 101 then 119.589

            elseif [DF] = 102 then 120.679

            elseif [DF] = 103 then 121.769

            elseif [DF] = 104 then 122.858

            elseif [DF] = 105 then 123.947

            elseif [DF] = 106 then 125.035

            elseif [DF] = 107 then 126.123

            elseif [DF] = 108 then 127.211

            elseif [DF] = 109 then 128.298

            elseif [DF] = 110 then 129.385

            elseif [DF] = 111 then 130.472

            elseif [DF] = 112 then 131.558

            elseif [DF] = 113 then 132.643

            elseif [DF] = 114 then 133.729

            elseif [DF] = 115 then 134.813

            elseif [DF] = 116 then 135.898

            elseif [DF] = 117 then 136.982

            elseif [DF] = 118 then 138.066

            elseif [DF] = 119 then 139.149

            elseif [DF] = 120 then 140.233

            elseif [DF] = 121 then 141.315

            elseif [DF] = 122 then 142.398

            elseif [DF] = 123 then 143.48

            elseif [DF] = 124 then 144.562

            elseif [DF] = 125 then 145.643

            elseif [DF] = 126 then 146.724

            elseif [DF] = 127 then 147.805

            elseif [DF] = 128 then 148.885

            elseif [DF] = 129 then 149.965

            elseif [DF] = 130 then 151.045

            elseif [DF] = 131 then 152.125

            elseif [DF] = 132 then 153.204

            elseif [DF] = 133 then 154.283

            elseif [DF] = 134 then 155.361

            elseif [DF] = 135 then 156.44

            elseif [DF] = 136 then 157.518

            elseif [DF] = 137 then 158.595

            elseif [DF] = 138 then 159.673

            elseif [DF] = 139 then 160.75

            elseif [DF] = 140 then 161.827

            elseif [DF] = 141 then 162.904

            elseif [DF] = 142 then 163.98

            elseif [DF] = 143 then 165.056

            elseif [DF] = 144 then 166.132

            elseif [DF] = 145 then 167.207

            elseif [DF] = 146 then 168.283

            elseif [DF] = 147 then 169.358

            elseif [DF] = 148 then 170.432

            elseif [DF] = 149 then 171.507

            elseif [DF] = 150 then 172.581

            elseif [DF] = 151 then 173.655

            elseif [DF] = 152 then 174.729

            elseif [DF] = 153 then 175.803

            elseif [DF] = 154 then 176.876

            elseif [DF] = 155 then 177.949

            elseif [DF] = 156 then 179.022

            elseif [DF] = 157 then 180.094

            elseif [DF] = 158 then 181.167

            elseif [DF] = 159 then 182.239

            elseif [DF] = 160 then 183.311

            elseif [DF] = 161 then 184.382

            elseif [DF] = 162 then 185.454

            elseif [DF] = 163 then 186.525

            elseif [DF] = 164 then 187.596

            elseif [DF] = 165 then 188.667

            elseif [DF] = 166 then 189.737

            elseif [DF] = 167 then 190.808

            elseif [DF] = 168 then 191.878

            elseif [DF] = 169 then 192.948

            elseif [DF] = 170 then 194.017

            elseif [DF] = 171 then 195.087

            elseif [DF] = 172 then 196.156

            elseif [DF] = 173 then 197.225

            elseif [DF] = 174 then 198.294

            elseif [DF] = 175 then 199.363

            elseif [DF] = 176 then 200.432

            elseif [DF] = 177 then 201.5

            elseif [DF] = 178 then 202.568

            elseif [DF] = 179 then 203.636

            elseif [DF] = 180 then 204.704

            elseif [DF] = 181 then 205.771

            elseif [DF] = 182 then 206.839

            elseif [DF] = 183 then 207.906

            elseif [DF] = 184 then 208.973

            elseif [DF] = 185 then 210.04

            elseif [DF] = 186 then 211.106

            elseif [DF] = 187 then 212.173

            elseif [DF] = 188 then 213.239

            elseif [DF] = 189 then 214.305

            elseif [DF] = 190 then 215.371

            elseif [DF] = 191 then 216.437

            elseif [DF] = 192 then 217.502

            elseif [DF] = 193 then 218.568

            elseif [DF] = 194 then 219.633

            elseif [DF] = 195 then 220.698

            elseif [DF] = 196 then 221.763

            elseif [DF] = 197 then 222.828

            elseif [DF] = 198 then 223.892

            elseif [DF] = 199 then 224.957

            elseif [DF] = 200 then 226.021

            elseif [DF] = 201 then 227.085

            elseif [DF] = 202 then 228.149

            elseif [DF] = 203 then 229.213

            elseif [DF] = 204 then 230.276

            elseif [DF] = 205 then 231.34

            elseif [DF] = 206 then 232.403

            elseif [DF] = 207 then 233.466

            elseif [DF] = 208 then 234.529

            elseif [DF] = 209 then 235.592

            elseif [DF] = 210 then 236.655

            elseif [DF] = 211 then 237.717

            elseif [DF] = 212 then 238.78

            elseif [DF] = 213 then 239.842

            elseif [DF] = 214 then 240.904

            elseif [DF] = 215 then 241.966

            elseif [DF] = 216 then 243.028

            elseif [DF] = 217 then 244.09

            elseif [DF] = 218 then 245.151

            elseif [DF] = 219 then 246.213

            elseif [DF] = 220 then 247.274

            elseif [DF] = 221 then 248.335

            elseif [DF] = 222 then 249.396

            elseif [DF] = 223 then 250.457

            elseif [DF] = 224 then 251.517

            elseif [DF] = 225 then 252.578

            elseif [DF] = 226 then 253.638

            elseif [DF] = 227 then 254.699

            elseif [DF] = 228 then 255.759

            elseif [DF] = 229 then 256.819

            elseif [DF] = 230 then 257.879

            elseif [DF] = 231 then 258.939

            elseif [DF] = 232 then 259.998

            elseif [DF] = 233 then 261.058

            elseif [DF] = 234 then 262.117

            elseif [DF] = 235 then 263.176

            elseif [DF] = 236 then 264.235

            elseif [DF] = 237 then 265.294

            elseif [DF] = 238 then 266.353

            elseif [DF] = 239 then 267.412

            elseif [DF] = 240 then 268.471

            elseif [DF] = 241 then 269.529

            elseif [DF] = 242 then 270.588

            elseif [DF] = 243 then 271.646

            elseif [DF] = 244 then 272.704

            elseif [DF] = 245 then 273.762

            elseif [DF] = 246 then 274.82

            elseif [DF] = 247 then 275.878

            elseif [DF] = 248 then 276.935

            elseif [DF] = 249 then 277.993

            elseif [DF] = 250 then 279.05

            else null end

            • 3. Re: Comparison of test statistic with critical value (chi squared test)
              Gerardo Varela

              Here is an example of the factorial function in Tableau, using Table Calc's, that may or may not help.

               

              Regards,

              Gerardo

              • 4. Re: Comparison of test statistic with critical value (chi squared test)
                Sam Cheadle

                Thanks very much for the replies.

                 

                I'm not able to convert the DF field into a dimension (possibly because it is a calculated field?), so I am unable to link the critical value data-source.

                 

                I like the idea of a calculated field with a series of if else statements. That would work.

                 

                Thanks also for also for the factorial function info!

                 

                Cheers

                Sam