baysgrmg.xls - Department of Family and Preventative Medicine

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					                                              02ec2c08-96da-4ba9-b352-b40ece40c251.xls



Bayesian Graph Pre-->Post Probability Calculator
(baysgrmg.xl4)
                              Clinical Decision Making Program
                              Department of Family Medicine, UOHSC

This calculator will produce a Bayesian Graph for a particular
test for a given disease. This calculator asks the names of the
disease and the test, and the sensitivity and specificity of the test.
It produces a graph, in which the user provides the prior probability and
test result, and reads off the posterior probability the patient has the disease.

This version magnifies the bottom end of the prior probability range, from 0 to 0.1.


For the specified disease, this will produce a curve that shows the posterior probability
given positive result and negative result of the test, for each of the range of pretest
probabilities.
                              (fill in)
Disease                       Disease name
Test name                     Test name
Sensitivity                            0.9
Specificity                            0.9

Calculation of posterior probability given positive or negative test result
is done in the section to the right.

Formula:
                              p(D/T+)=    p(T+/D)*p(D)
                                          p(T+/D)*p(D)+p(T+/D-)*p(D-)

                              p(D/T-)=    p(T-/D)*p(D)
                                          p(T-/D)*p(D)+p(T-/D-)*p(D-)




Disease                                   Disease name
Test name                                 Test name

                         Bayesian Graph: Post-test probability as function of test
                            result and pre-test probability, for range 0 to 0.1.


                      0.550
                      0.500
                      0.450
                      0.400                                                                 0.03
   test Probability




                                                                                             0.0
                      0.350

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                                                        02ec2c08-96da-4ba9-b352-b40ece40c251.xls


   Post-test Probability   0.350                                                                                            0.04
                           0.300                                                                                            0.04
                                                                                                                            0.04
                           0.250                                                                                            0.04
                                                                                                                            0.04
                           0.200
                                                                                                                            0.04
                           0.150                                                                                            0.04
                                                                                                                            0.04
                           0.100                                                                                            0.04
                           0.050                                                                                             0.0
                                                                                                                            0.05
                           0.000                                                                                            0.05
                                   0    0.01     0.02     0.03       0.04     0.05    0.06     0.07    0.08   0.09    0.1   0.05
                                                                                                                            0.05
                                                                     Pre-test Probability                                   0.05
                                                                                                                            0.05
                                   Probability given Positive Test          Probability given Negative Test    If no test   0.05
                                                                                                                            0.05
                                                                                                                            0.05
                                                                                                                             0.0
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                            0.06
                                                                                                                             0.0




Clinical Decision Making Spreadsheet Calculator

Robert M. Hamm, PhD
Clinical Decision Making Program
Department of Family Medicine
University of Oklahoma Health Sciences Center
Oklahoma City OK 73190
405/271-8167
Fax: 405/271-4125
email: rob-hamm@uokhsc.edu




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02ec2c08-96da-4ba9-b352-b40ece40c251.xls




                Page 3
                   02ec2c08-96da-4ba9-b352-b40ece40c251.xls




Prior          Posterior      Posterior      Diagonal
Probability    Probability    Probability    Line
               Pos Result     Neg Result
               Probability given Positive givenno test
Prior Probability                            If
                              Probability Test Negative Test
            0          0.000          0.000               0
        0.001          0.009          0.000          0.001
        0.002          0.018          0.000          0.002
        0.003          0.026          0.000          0.003
        0.004          0.035          0.000          0.004
        0.005          0.043          0.001          0.005
        0.006          0.052          0.001          0.006
        0.007          0.060          0.001          0.007
        0.008          0.068          0.001          0.008
        0.009          0.076          0.001          0.009
         0.01          0.083          0.001            0.01
        0.011          0.091          0.001          0.011
        0.012          0.099          0.001          0.012
        0.013          0.106          0.001          0.013
        0.014          0.113          0.002          0.014
        0.015          0.121          0.002          0.015
        0.016          0.128          0.002          0.016
        0.017          0.135          0.002          0.017
        0.018          0.142          0.002          0.018
        0.019          0.148          0.002          0.019
         0.02          0.155          0.002            0.02
        0.021          0.162          0.002          0.021
        0.022          0.168          0.002          0.022
        0.023          0.175          0.003          0.023
        0.024          0.181          0.003          0.024
        0.025          0.188          0.003          0.025
        0.026          0.194          0.003          0.026
        0.027          0.200          0.003          0.027
        0.028          0.206          0.003          0.028
        0.029          0.212          0.003          0.029
         0.03          0.218          0.003            0.03
        0.031          0.224          0.004          0.031
        0.032          0.229          0.004          0.032
        0.033          0.235          0.004          0.033
        0.034          0.241          0.004          0.034
        0.035          0.246          0.004          0.035
        0.036          0.252          0.004          0.036
        0.037          0.257          0.004          0.037
        0.038          0.262          0.004          0.038
        0.039          0.268          0.004          0.039
         0.04          0.273          0.005            0.04


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        02ec2c08-96da-4ba9-b352-b40ece40c251.xls


0.041     0.278        0.005       0.041
0.042     0.283        0.005       0.042
0.043     0.288        0.005       0.043
0.044     0.293        0.005       0.044
0.045     0.298        0.005       0.045
0.046     0.303        0.005       0.046
0.047     0.307        0.005       0.047
0.048     0.312        0.006       0.048
0.049     0.317        0.006       0.049
 0.05     0.321        0.006        0.05
0.051     0.326        0.006       0.051
0.052     0.331        0.006       0.052
0.053     0.335        0.006       0.053
0.054     0.339        0.006       0.054
0.055     0.344        0.006       0.055
0.056     0.348        0.007       0.056
0.057     0.352        0.007       0.057
0.058     0.357        0.007       0.058
0.059     0.361        0.007       0.059
 0.06     0.365        0.007        0.06
0.061     0.369        0.007       0.061
0.062     0.373        0.007       0.062
0.063     0.377        0.007       0.063
0.064     0.381        0.008       0.064
0.065     0.385        0.008       0.065
0.066     0.389        0.008       0.066
0.067     0.393        0.008       0.067
0.068     0.396        0.008       0.068
0.069     0.400        0.008       0.069
 0.07     0.404        0.008        0.07
0.071     0.408        0.008       0.071
0.072     0.411        0.009       0.072
0.073     0.415        0.009       0.073
0.074     0.418        0.009       0.074
0.075     0.422        0.009       0.075
0.076     0.425        0.009       0.076
0.077     0.429        0.009       0.077
0.078     0.432        0.009       0.078
0.079     0.436        0.009       0.079
 0.08     0.439        0.010        0.08
0.081     0.442        0.010       0.081
0.082     0.446        0.010       0.082
0.083     0.449        0.010       0.083
0.084     0.452        0.010       0.084
0.085     0.455        0.010       0.085
0.086     0.459        0.010       0.086
0.087     0.462        0.010       0.087
0.088     0.465        0.011       0.088
0.089     0.468        0.011       0.089
 0.09     0.471        0.011        0.09
0.091     0.474        0.011       0.091
0.092     0.477        0.011       0.092


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         02ec2c08-96da-4ba9-b352-b40ece40c251.xls


0.093      0.480        0.011       0.093
0.094      0.483        0.011       0.094
0.095      0.486        0.012       0.095
0.096      0.489        0.012       0.096
0.097      0.492        0.012       0.097
0.098      0.494        0.012       0.098
0.099      0.497        0.012       0.099
   0.1     0.500        0.012          0.1




                         Page 6
                                  02ec2c08-96da-4ba9-b352-b40ece40c251.xls




Prior          Posterior       Posterior       Diagonal
Probability    Probability     Probability     Line
               Pos Result      Neg Result
               Probability given Positive givenno test
Prior Probability                              If
                               Probability Test Negative Test
            0          0.000            0.000              0
         0.01          0.083            0.001           0.01
         0.02          0.155            0.002           0.02
         0.03          0.218            0.003           0.03
           Bayesian Graph: Post-test probability as function of test
         0.04          0.273            0.005           0.04
         0.05                           and
                       0.321 result 0.006 pre-test0.05   probability
         0.06          0.365            0.007           0.06
         0.07          0.404            0.008           0.07
       1.000
         0.08          0.439            0.010           0.08
         0.09          0.471            0.011           0.09
       0.900
          0.1          0.500            0.012            0.1
       0.800
         0.11          0.527            0.014           0.11
   Post-test Probability




         0.12
       0.700           0.551            0.015           0.12
         0.13          0.574            0.016           0.13
       0.600
         0.14          0.594            0.018           0.14
         0.15
       0.500           0.614            0.019           0.15
         0.16          0.632            0.021           0.16
       0.400
         0.17          0.648            0.022           0.17
         0.18
       0.300           0.664            0.024           0.18
         0.19          0.679            0.025           0.19
       0.200
          0.2          0.692            0.027            0.2
       0.100
         0.21          0.705            0.029           0.21
         0.22          0.717            0.030           0.22
       0.000
         0.23          0.729            0.032           0.23
         0.24 0        0.7400.2
                     0.1             0.30.0340.4    0.50.240.6      0.7    0.8     0.9  1      1.1
         0.25          0.750            0.036 Pre-test0.25
                                                         Probability
         0.26          0.760            0.038           0.26
         0.27          0.769            0.039           0.27
                Probability given Positive Test      Probability given Negative Test   If no test
         0.28          0.778            0.041           0.28
         0.29          0.786            0.043           0.29
          0.3          0.794            0.045            0.3
         0.31          0.802            0.048           0.31
         0.32          0.809            0.050           0.32
         0.33          0.816            0.052           0.33
         0.34          0.823            0.054           0.34
         0.35          0.829            0.056           0.35
         0.36          0.835            0.059           0.36
         0.37          0.841            0.061           0.37
         0.38          0.847            0.064           0.38
         0.39          0.852            0.066           0.39
          0.4          0.857            0.069            0.4


                                                      Page 7
               02ec2c08-96da-4ba9-b352-b40ece40c251.xls


0.41   0.862     0.072         0.41
0.42   0.867     0.074         0.42
0.43   0.872     0.077         0.43
0.44   0.876     0.080         0.44
0.45   0.880     0.083         0.45
0.46   0.885     0.086         0.46
0.47   0.889     0.090         0.47
0.48   0.893     0.093         0.48
0.49   0.896     0.096         0.49
 0.5   0.900     0.100          0.5
0.51   0.904     0.104         0.51
0.52   0.907     0.107         0.52
0.53   0.910     0.111         0.53
0.54   0.914     0.115         0.54
0.55   0.917     0.120         0.55
0.56   0.920     0.124         0.56
0.57   0.923     0.128         0.57
0.58   0.926     0.133         0.58
0.59   0.928     0.138         0.59
 0.6   0.931     0.143          0.6
0.61   0.934     0.148         0.61
0.62   0.936     0.153         0.62
0.63   0.939     0.159         0.63
0.64   0.941     0.165         0.64
0.65   0.944     0.171         0.65
0.66   0.946     0.177         0.66
0.67   0.948     0.184         0.67
0.68   0.950     0.191         0.68
0.69   0.952     0.198         0.69
 0.7   0.955     0.206          0.7
0.71   0.957     0.214         0.71
0.72   0.959     0.222         0.72
0.73   0.961     0.231         0.73
0.74   0.962     0.240         0.74
0.75   0.964     0.250         0.75
0.76   0.966     0.260         0.76
0.77   0.968     0.271         0.77
0.78   0.970     0.283         0.78
0.79   0.971     0.295         0.79
 0.8   0.973     0.308          0.8
0.81   0.975     0.321         0.81
0.82   0.976     0.336         0.82
0.83   0.978     0.352         0.83
0.84   0.979     0.368         0.84
0.85   0.981     0.386         0.85
0.86   0.982     0.406         0.86
0.87   0.984     0.426         0.87
0.88   0.985     0.449         0.88
0.89   0.986     0.473         0.89
 0.9   0.988     0.500          0.9
0.91   0.989     0.529         0.91
0.92   0.990     0.561         0.92


                               Page 8
               02ec2c08-96da-4ba9-b352-b40ece40c251.xls


0.93   0.992     0.596         0.93
0.94   0.993     0.635         0.94
0.95   0.994     0.679         0.95
0.96   0.995     0.727         0.96
0.97   0.997     0.782         0.97
0.98   0.998     0.845         0.98
0.99   0.999     0.917         0.99
   1   1.000     1.000            1




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