



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
Webbased 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.
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.

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
Notest/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.

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.

oddsrat.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.

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.

oddsrat.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.

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.

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 ztransformation
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.

oddprob.xls

Odds and probabilities

Translates between odds
and probabilities. Graphs the relations.

Chisq2x2.xls

Chisquared test

Calculates
Chisquared 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) 2718000 x 32306 Fax (405) 2712784
roberthamm@ouhsc.edu
http://www.fammed.ouhsc.edu/robhamm/index2.htm
