



Clinical Decision Making
Calculators
The CDM calculators
are of the following types:
Judgment Research Calculators
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 mouse button (PC  right button) and
select "Save link as..." to download the file. These are Excel
files, and their extension is .XLS or .XLSX. 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 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 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 predicting the probability of a category.

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) 2715362 x 32306 Fax (405) 2712784
roberthamm@ouhsc.edu
http://www.fammed.ouhsc.edu/robhamm/index2.htm
