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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.
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File Name
(Click, hold mouse button, select "save as" to download)
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Calculator name
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Function of
calculator
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eutree.xls
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Decision Tree: Expected
Utility
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You specify
probabilities of branches and utilities of outcomes, it calculates expected
utility.
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discount.xls
discountmonths.xls
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Utility Discount Rate
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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.
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File Name
(Click the ".xls" file, hold mouse button, select "save
as" to download)
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Calculator name
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Function of
calculator
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2x2count.xls
Tutorial
Web Calculator (Vassar)
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Contingency table (test
by disease): counts from probabilities
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You specify base rate,
sensitivity, specificity, it produces counts in 2 by 2 table plus other
statistics.
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2x2probs.xls
Tutorial
Web Calculator
(CEBM)
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Contingency table (test
by disease): probs. from counts
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You put counts in cells
of 2 by 2 table, it produces sensitivity, specificity, etc.
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2x2p&ci.xls
Tutorial
Web Calculator
(CEBM)
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Contingency table (test
by disease) with confidence intervals on each probability
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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.
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baystree.xls
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Decision Tree: Bayes'
Theorem
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You specify base rate,
specificity, and sensitivity. It demonstrates "inversion" of a
tree.
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lhoodrat.xls
Web Nomogram
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Bayes' Theorem in the
Odds/Likelihood ratio form.
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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.
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baysgrph.xls
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Bayesian graph
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You specify sensitivity
and specificity of a test, it prints posterior probability as a function of
any prior probability.
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baysgrmg.xls
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Bayesian graph for
diseases with low prior probability
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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.
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baygphth.xls
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Bayesian graph with
thresholds
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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
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bgphthut.xls
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Bayesian graph with
thresholds based on utilities
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As with Bayesian graph
with thresholds; plus you specify the utilities upon which a threshold
would be based.
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ScrnPers.xls
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Screening perspective
calculator
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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.
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2tstindp.xls
Tutorial
Presentation (European Society for Medical
Decision Making, 1999)
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Explore implications of
2 diagnostic tests - are they independent or correlated?
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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.
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3tstindp.xls
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Explore implications of
3 diagnostic tests - are they independent or correlated?
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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.
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File Name
(Click hold mouse button, select "save as" to Download)
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Calculator name
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Function of
calculator
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exposdis.xls
Web Calculator
(CEBM)
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Contingency table
showing outcomes (disease) as an effect of exposure
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You specify data about
the relation between exposure and disease, it produces statistics (relative
risk, etc.)
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NNP.xls
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Number Needed to
Protect
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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.
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NNPcost.xls
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Number Needed to
Protect and Cost
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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.
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odds-rat.xls
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Odds ratio: contingency
between treatment or exposure and outcome
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You specify the
contingency table, it calculates odds ratio. Allows this to be done from
various starting points.
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2trtindp.xls
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2 Treatment Independence
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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.
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2trtindpkram.xls
Tutorial
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2 Treatment Independence,
diagnosis framework
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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.
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File Name
(Click the ".xls" file, hold mouse button, select "save
as" to download)
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Calculator name
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Function of calculator
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treatout.xls
Treatout
tutorial
Web Calculator (CEBM)
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Contingency table:
outcome as an effect of treatment
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You specify the data
relating treatment to outcome, it calculates odds ratio, etc.
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casecont.xls
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Contingency table
statistics appropriate for case/control designs.
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You enter data from a
case control study, it produces valid statistics for generalization.
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besd.xls
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Binary Effect Size
Display (BESD)
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You specify a
contingency table showing an effect (treatment/outcome), it expresses the
relation as correlation, etc.
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NNT.xls
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Number needed to treat
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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.
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NNTcost.xls
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Number Needed to Treat
and Cost
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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.
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odds-rat.xls
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Odds ratio: contingency
between treatment or exposure and outcome
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You specify the
contingency table, it calculates odds ratio. Allows this to be done from
various starting points.
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ORexplor.xls
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Odds Ratio explorer -
from retrospective to prospective context
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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.
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Yearates.xls
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Yearly Rates.
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Translates outcome
rates for treated and nontreated conditions (or Odds Ratio) in a multiyear
study into annual rates.
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File Name
(Click the ".xls" file, hold mouse button, select "save
as" to download)
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Calculator name
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Function of
calculator
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BMI.xls
Web
calculator (by Jim Cacy, in JavaScript)
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Body Mass Index
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You specify height,
weight (in metric or English units), it calculates Body Mass Index.
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FPIR.xls
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Family Practice
Incidence Rate
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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.
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NmNeedTr.xls
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Number needed to treat
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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.
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File Name
(Click hold mouse button, select "save as" to Download)
|
Calculator name
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Function of
calculator
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Confin95.xls
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95% confidence
intervals
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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.
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ProbCI.xls
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Confidence interval for
probabilities, proportions
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You specify the number
of events and the total number of observations, it calculates the
confidence interval for that probability.
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fishersz.xls
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Fisher z-transformation
for doing statistical tests on correlations
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You specify
correlation, it produces Fisher's Z transformation. And the reverse.
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logit.xls
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Logit and logistic
functions demonstrated
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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.
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odd-prob.xls
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Odds and probabilities
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Translates between odds
and probabilities. Graphs the relations.
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Chisq2x2.xls
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Chi-squared test
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Calculates
Chi-squared statistic and probability for 2 by n tables, for n = 2 through
7.
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RatePower.xls
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Rate or Proportion
Confidence Interval & Power Estimation Calculator
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Calculate the power
that a rate will exceed a target rate given N.
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TripTria.xls
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Triplet
Triangulator
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Places
a triplet of numbers in trilinear coordinates within a triangle.
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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/index.htm
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