# baysgrmg.xls - Department of Family and Preventative Medicine

Document Sample

```					                                              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

Page 1
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

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

Page 2
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

Page 4
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

Page 5
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

Page 9

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 2 posted: 11/20/2011 language: pages: 9