HOW
TO USE DAG_Stat 
HOW
TO USE DAG_Stat
InputOther
ControlsResultsStatistics
for Diagnostic TestsStatistics
for Interrater AgreementOther
IndicesOther
OutputNotes
INPUT
It is also possible to enter your own name for the disease or condition being diagnosed and the name of the test. This may be useful to help you identify output, but it has no effect on any statistic calculations.
The probability
coverage of the confidence intervals may also be changed as
below
Normally 95% confidence
intervals are reported, but any value greater than 0 and less than
100% may be entered.
Four buttons active macros that perform a number of functions.
removes all four cell entries.
forces recalculation of the results. This button is useful with
older, slower computers. Calculation may be set to manual (on the
Options command in Tools menu). This prevents Excel from
recalculating statistics as each cell is entered. After all four
values are input, the Calculate button is then pressed. This option
is unnecessary on modern, fast machines.
displays appropriate Diagnosic Test indices in percent
form.
displays appropriate Diagnosic Test indices in percent
form.
Statistics for Diagnostic Tests
DAG_Stat produces a comprehensive range of indices that are widely used in the assessment of the performance of diagnostic tests. In addition, a number of less well known indices such as the sensitivity of a test working at a random level of performance and an index of senstivity that adjusts for this (the quality index) are produced. Some indices, such as Youden's index have been included principally to allow comparison with published results rather than because they are recommended statistics.
Each index is briefly explained in a pop-up comment that will appear when you place the mouse over the at the top righthand corner of the index name. (N.B. This feature is not available in earlier versions of Excel and, depending on how your copy of Excel is configured, may need to be activated.)
Interrater
Agreement Statistics
DAG_Stat calculates
Cohen's Kappa, associated standard error and test of the hypothesis
that kappa differs from zero. It also shows the observed agreement
and that expected by chance alone. A standardized description of the
magnitute of agreement is provided. More information about the nature
of agreement (or disagreement) can be gained by considering agreement
for positive and negative judgements separately. This is acheived
through indices of positive and negative agreement. Difference in the
judged prevalence of an outcome and the relative frequency of
positive versus negative outcomes can affect Kappa. Byrt's indices
and adjustments can assist in identifying these effects.
McNemar's
test may also
be useful in this regard.
A large number of other indices have been proposed as measures of agreement or have theoretical models that are relevant to the performance of tests or judges. DAG_Stat calculates a wide range of these measures. It should be noted that many of these indices have substantial limitations or are based on models that may not be relevant to particular situations. These statistics are provided principally to allow comparison with published results.
The chi-square test (both Pearson and likelihood ratio) is calculated as a general test of independence of the test and criterion. McNemar's test in this application tests for differences in judged prevalence of the disorder being studied.
A table of percentages in each cell is provided beside the input cells.
In addition to output in tabular form, test statistics are also produced in an abbreviated form for copying and pasting into reports. The number of decimal places used in these summaries is specified at the top of the sheet.
"Sensitivity = 0.85 (95% CI: 0.82 - 0.88)"
"Sensitivity = 0.8538 (95% CI: 0.8216 - 0.8822)"
Notes
Some indices cannot be
calculated when one or more cell entries are zero. A warning is
displayed under these conditions. Low expected frequencies may
invalidate the chi-square test. Accordingly, the number of cells with
expected frequencies below 5 and below 1 are reported.
As downloaded, each sheet is protected from modification. Only the shaded cells on the Statistics worksheet may be changed. If you wish to modify the sheet, choose the "Unprotect Sheet..." option from the "Protection" command on the "Tools" menu.