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 files, and their extension is .XLS. 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 ".XLS" 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.

Decision Analysis Calculators

File Name
(Click, hold mouse button, select "save as" to download)

Calculator name

Function of calculator

eutree.xls

Decision Tree: Expected Utility

You specify probabilities of branches and utilities of outcomes, it calculates expected utility.

discount.xls

discountmonths.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 ".xls" file, hold mouse button, select "save as" to download)

Calculator name

Function of calculator

2x2count.xls

Tutorial

Web Calculator (Vassar)

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.xls

Tutorial

Web Calculator (CEBM)

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.xls

Tutorial

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.xls

Decision Tree: Bayes' Theorem

You specify base rate, specificity, and sensitivity. It demonstrates "inversion" of a tree.

lhoodrat.xls

Web Nomogram

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.

LogBayes.xls

Log Odds Version of Bayes’ Theorem

You specify prior probability, sensitivity, specificity, and test result for a series of tests. It graphs Bayes' Theorem calculations in Log(odds) scale.

baysgrph.xls

Bayesian graph

You specify sensitivity and specificity of a test, it prints posterior probability as a function of any prior probability.

baysgrmg.xls

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.xls

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.xls

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.xls

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.

EntropyUncertainty.xlsx

Explore the use of “negative entropy” to measure uncertainty

You specify prior probability of a disease, and the sensitivity and specificity of a test. It shows probability of a positive or negative test, post test result probabilities, the pretest uncertainty, and the expected posttest uncertainty.

2tstindp.xls

Tutorial

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 constructs the corresponding data set, and gives post test probabilities for all combinations of test results.

3tstindp.xls

Explore implications of 3 diagnostic tests - are they independent or correlated?

You specify the characteristics of 3 diagnostic tests for a disease (prior probability, sensitivities and specificities, and correlations when disease is present and when absent. It constructs the corresponding data set, 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.xls

Web Calculator (CEBM)

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.xls

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.xls

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.xls

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.xls

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.xls

Tutorial

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 ".xls" file, hold mouse button, select "save as"  to download)

Calculator name

Function of calculator

treatout.xls

Treatout tutorial

Web Calculator (CEBM)

Contingency table: outcome as an effect of treatment

You specify the data relating treatment to outcome, it calculates odds ratio, etc.

casecont.xls

Contingency table statistics appropriate for case/control designs.

You enter data from a case control study, it produces valid statistics for generalization.

besd.xls

Binary Effect Size Display (BESD)

You specify a contingency table showing an effect (treatment/outcome), it expresses the relation as correlation, etc.

NNT.xls

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.xls

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.xls

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.xls

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.xls

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 ".xls" file, hold mouse button, select "save as"  to download)

Calculator name

Function of calculator

BMI.xls

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.xls

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.xls

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.

Statistics Calculators

File Name
(Click hold mouse button, select "save as" to Download)

Calculator name

Function of calculator

Confin95.xls

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.xls

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.xls

Fisher z-transformation for doing statistical tests on correlations

You specify correlation, it produces Fisher's Z transformation. And the reverse.

logit.xls

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.xls

Odds and probabilities

Translates between odds and probabilities. Graphs the relations.

Chisq2x2.xls

Chi-squared test

Calculates Chi-squared statistic and probability for 2 by n tables, for n = 2 through 7.

RatePower.xls

 

Rate or Proportion Confidence Interval & Power Estimation Calculator

Calculate the power that a rate will exceed a target rate given N.

TripTria.xls

Triplet Triangulator

Places a triplet of numbers in trilinear coordinates within a triangle.

Questions? Contact:

Robert M. Hamm, PhD, Professor
Director, Clinical Decision Making Program
Department of Family and Preventive Medicine
University of Oklahoma Health Sciences Center
900 NE 10th Street, Oklahoma City, OK  73104
Phone (405) 271-8000 x 32306 Fax (405) 271-2784
robert-hamm@ouhsc.edu
http://www.fammed.ouhsc.edu/robhamm/index2.htm

 

 

Department of Family and Preventive Medicine
The University of Oklahoma Health Sciences Center
P.O. Box 26901
Oklahoma City, OK 73190

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