Clinical Decision Making Calculators
The CDM calculators are of the following types:
Decision Analysis Calculators
Disease/Test Relation Calculators
Exposure/Disease Relation Calculators
Treatment/Outcome Relation Calculators
Calculators Useful in the Clinic.
Statistics Calculators
Tutorials for some of the calculators
Comparison of Web-based versus spreadsheet calculators. (Presented at Aerospace Human Factors Society meetings, Detroit, May 20, 1999.)
Each spreadsheet performs a common calculation useful for clinical decisions or for analyzing data pertinent to clinical decisions.
You must download the files, then run them using your own spreadsheet program. Hold down the mousebutton (PC - right button) and select "Save link as..."to download the file. These are Excel 4.0 or Excel 5.0 files, and their extension is .XL4. They run on Macintosh or DOS/Windows computers.
After you have downloaded the files, you might find it necessary to open your spreadsheet, then load the file using the spreadsheet's "open" command, rather than clicking on the name of the file, because your operating system may not recognize that an ".XL4" file is a spreadsheet file.
(If your browser does not download these correctly when you click on them.)
These calculator spreadsheets are made available by Rob Hamm, PhD, in the Clinical Decision Making Program, Department of Family and Preventive Medicine, University of Oklahoma Health Sciences Center.
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| File Name (Click, hold mouse button, select "save as" to download) | Calculator name | Function of calculator |
| eutree.xl4 | Decision Tree: Expected Utility | You specify probabilities of branches and utilities of outcomes, it calculates expected utility. |
| Discount.xls | Utility Discount Rate | Calculates a person's temporal discount rate. Assumes person has already made a judgment setting equivalent two life streams - one with a time of sickness at the beginning, the other with a period of sickness at the end.
If either time period is measured in months, use "discountmonths.xls" which is very large. |
Disease/Test Relation Calculators
| File Name (Click the ".xl4" file, hold mouse button, select "save as" to download) | Calculator name | Function of calculator |
| 2x2count.xl4 | Contingency table (test by disease): counts from probabilities | You specify base rate, sensitivity, specificity, it produces counts in 2 by 2 table plus other statistics. |
| 2x2probs.xl4 | Contingency table (test by disease): probs. from counts | You put counts in cells of 2 by 2 table, it produces sensitivity, specificity, etc. |
| 2x2p&ci.xl4 | Contingency table (test by disease) with confidence intervals on each probability | As with 2x2probs, you put counts in cells of 2 by 2 table; it produces the list of probabilities, and gives the confidence interval for each. |
| baystree.xl4 | Decision Tree: Bayes' Theorem | You specify base rate, specificity, and sensitivity. It demonstrates "inversion" of a tree. |
| lhoodrat.xl4 | Bayes' Theorem in the Odds/Likelihood ratio form. | You specify Prior Odds the patient has disease, and likelihood ratio of seeing test results, given patient has the disease or does not have the disease; it calculates posterior odds. |
| baysgrph.xl4 | Bayesian graph | You specify sensitivity and specificity of a test, it prints posterior probability as a function of any prior probability. |
| baysgrmg.xl4 | Bayesian graph for diseases with low prior probability | You specify sensitivity and specificity of a test, for a disease with a low prior probability (less than 10%). It prints posterior probability as a function of prior probability in the 0 to 0.1 range. |
| baygphth.xl4 | Bayesian graph with thresholds | As with Bayesian graph; plus you specify a treatment threshold and it specifies and graphs a No-test/Test Threshold and a Test/Treat Threshold |
| bgphthut.xl4 | Bayesian graph with thresholds based on utilities | As with Bayesian graph with thresholds; plus you specify the utilities upon which a threshold would be based. |
| ScrnPers.xl4 | Screening perspective calculator | You specify the base rate for a condition, the number of people screened, and the sensitivity and specificity of a screening test, and it displays a tree showing the numbers with/without the disease and with true and false screen results. |
| 2tstindp.xl4
Presentation (European Society for Medical Decision Making, 1999) | Explore implications of 2 diagnostic tests - are they independent or correlated? | You specify the characteristics of 2 diagnostic tests for a disease (prior probability, sensitivities and specificities, and correlation when disease is present and when absent. It gives post test probabilities for all combinations of test results. |
Exposure/Disease Relation Calculators
| File Name (Click hold mouse button, select "save as" to Download) | Calculator name | Function of calculator |
| exposdis.xl4 | Contingency table showing outcomes (disease) as an effect of exposure | You specify data about the relation between exposure and disease, it produces statistics (relative risk, etc.) |
| NNP.xl4 | Number Needed to Protect | You specify the effect of an exposure (probability of bad outcome without the exposure and with the exposure), it produces the number of people you would need to protect to prevent one bad outcome. |
| NNPcost.xl4 | Number Needed to Protect and Cost | You specify the effect of an exposure (probability of bad outcome without the exposure and with the exposure), it produces the number of people you would need to protect to prevent one bad outcome. You specify the cost of protecting one person from exposure. It says whether it is worth protecting a person from exposure, and gives thresholds on NNP and Cost of Protecting. |
| odds-rat.xl4 | Odds ratio: contingency between treatment or exposure and outcome | You specify the contingency table, it calculates odds ratio. Allows this to be done from various starting points. |
| 2trtindp.xl4 | 2 Treatment Independence | To explore dependencies between exposure to two risk factors or treatments. One dependency is correlation between the factors. The other dependency is the effects of one factor being different for different levels of the other factor. |
| 2trtindpkram.xl4 | 2 Treatment Independence, diagnosis framework | To explore dependencies between exposure to two risk factors or treatments. This follows Kraemer et al (1999 Psychological Methods) in speaking of the "sensitivity" and "specificity" of the risk factor for the outcome. In calculation, it is identical to the 2 Test Independence calculator (see above) and so you can use that one's tutorial. The dependencies are the correlations between the two risk factors' false negatives, and between their false positives. |
Treatment/Outcome Relation Calculators
| File Name (Click the ".xl4" file, hold mouse button, select "save as" to download) | Calculator name | Function of calculator |
| treatout.xl4 | Contingency table: outcome as an effect of treatment | You specify the data relating treatment to outcome, it calculates odds ratio, etc. |
| casecont.xl4 | Contingency table statistics appropriate for case/control designs. | You enter data from a case control study, it produces valid statistics for generalization. |
| besd.xl4 | Binary Effect Size Display (BESD) | You specify a contingency table showing an effect (treatment/outcome), it expresses the relation as correlation, etc. |
| NmNeedTr.xl4 | Number needed to treat | You specify the effect of a treatment (probability of bad outcome without the treatment and with the treatment), it produces the number of patients you would need to treat to prevent one bad outcome. |
| NNTcost.xl4 | Number Needed to Treat and Cost | You specify the effect of a treatment (relating the probability of bad outcome without the treatment and with the treatment), it produces the number of people you would need to treat to prevent one bad outcome. You specify the cost of treating one person. It says whether it is worth treating one person, and gives thresholds on NNT and Cost of Treating. |
| odds-rat.xl4 | Odds ratio: contingency between treatment or exposure and outcome | You specify the contingency table, it calculates odds ratio. Allows this to be done from various starting points. |
| ORexplor.xl4 | Odds Ratio explorer - from retrospective to prospective context | Demonstrates why it is appropriate to use the Odds Ratio derived from a case control study, in a prospective context, and why OR is a good "control variable" for a sensitivity analysis. |
| Yearates.xl4 | Yearly Rates. | Translates outcome rates for treated and nontreated conditions (or Odds Ratio) in a multiyear study into annual rates. |
Calculators Useful in the Clinic
| File Name (Click the ".xl4" file, hold mouse button, select "save as" to download) | Calculator name | Function of calculator |
| BMI.xl4
Web calculator (by Jim Cacy, in JavaScript) | Body Mass Index | You specify height, weight (in metric or English units), it calculates Body Mass Index. |
| FPIR.xl4 | Family Practice Incidence Rate | You specify the size of a doctor's practice, and the rate a disease occurs. It specifies the number the doctor could expect to see in a year. |
| NmNeedTr.xl4 | Number needed to treat | You specify the effect of a treatment (probability of bad outcome without the treatment and with the treatment), it produces the number of patients you would need to treat to prevent one bad outcome. |
| File Name (Click hold mouse button, select "save as" to Download) | Calculator name | Function of calculator |
| Confin95.xl4 | 95% confidence intervals | You specify the confidence interval you are interested in, it calculates the interval around an effect size estimate for: differences, relative risk, relative risk reduction, and odds ratio. |
| ProbCI.xl4 | Confidence interval for probabilities, proportions | You specify the number of events and the total number of observations, it calculates the confidence interval for that probability. |
| fishersz.xl4 | Fisher z-transformation for doing statistical tests on correlations | You specify correlation, it produces Fisher's Z transformation. And the reverse. |
| logit.xl4 | Logit and logistic functions demonstrated | You state a number, it produces the logit; likewise for the logistic function (inverse of the logit). Demonstrates the basis of logistic regression for handling probabilistic predictions. |
| odd-prob.xl4 | Odds and probabilities | Translates between odds and probabilities. Graphs the relations. |
| Chisq2x2.xl4 | Chi-squared test | Calculates Chi-squared statistic and probability for 2 by n tables, for n = 2 through 7. |
Questions? Contact:
Robert M. Hamm, PhD,Associate
Professor
Director, Clinical Decision Making Program
Dept. of Family and Preventive Medicine
U of Oklahoma Health Sciences Center
900 NE 10th St., Oklahoma City OK 73104
405/271-8000 x 32302 Fax 405/271-2784
robert-hamm@ouhsc.edu
http://www.fammed.ouhsc.edu/robhamm/index.htm
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since 2/23/99.