Prior
to the selection of the Statistically Valid Random Sample (SVRS),
the claims universe shall also be properly focused and analyzed
to determine the sampling plan and methodology. Focusing the universe
is performed by targeting specific claims which match the approach
and/or allegations of the case, and removing unnecessary low dollar
claims. The overall sampling plan and methodology may include a
stratified sampling approach consisting of one or more SVRS(s) and/or
100% claims audit(s).
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In order
to determine the probable scope and extent of overpayments, regardless
of how the overpayment was incurred, a SVRS shall be drawn from
each identified stratum (or the entire universe of claims in some
cases). Denied claims or claims where TRICARE paid zero dollars
shall always be removed from the Universe prior to stratification
and sampling. Only netted records shall be used.
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This
primary sample shall be selected using a random number generator
with a known seed number. Using a known non-zero seed number is
critical, as it will provide for the reproduction of the same set of
random numbers with the same sample and universe.
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The sample
size shall be calculated using the following parameters:
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• 90% confidence
level
• 10% precision
level
• 50% occurrence
rate (if there is no established rate of occurrence) or an estimate
of the occurrence rate from a previously documented statistically
valid analysis (by a Federal health care entitlement program) of
the units of audit (e.g., same provider, same procedures, same time
period) of the possible fraud.
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An oversample
of 20% shall always be randomly selected from the specific stratum
or universe, and audited with the primary sample at the beginning
of an audit.
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In all
claim audits using statistical techniques to extrapolate findings
of a sample to a specific stratum or a universe of claims, the audit
addresses the average overpayment per claim as the single unit of measurement.
The claim and the explanation of benefits are the evidentiary documents
which demonstrate the billed services submitted by a provider or
beneficiary and the payments made to a provider or beneficiary.
The claim is compared to the contents of the medical record to validate whether
a service was provided, whether it was provided at the level billed,
whether it was provided by the authorized provider shown on the
claim, or any other information which may be relevant to identify a
dollar loss to the Government. This information shall be recorded
on a summary spreadsheet generated by Microsoft® Excel, or compatible
software, with a .xls file extension for compatibility with other
widely used spreadsheet software (typically, the DHA Random Sample
Audit Worksheet shall be included for each SVRS). Each claim in
the sample shall be listed on the summary spreadsheet and the overpayment
totaled. When no overpayment exists, the claim shall appear on the
summary spreadsheet with zero listed as the overpayment.
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Each
claim of the audited oversample shall also be included with the
case, either as part of the summary spreadsheet or as part of a
separate spreadsheet.
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The overpayments
shall be expressed in dollars and cents. The total shall then be
summed and divided by the number of claims in the sample (remembering
that claims with no overpayments are shown in the column to be summed
as zero). The product is the average mean overpayment per claim
in the sample. The average mean overpayment per claim in the sample
shall be multiplied by the number of claims in the specific stratum
or universe from which the sample and oversample was taken, and
this product expressed in dollars and cents is the extrapolated
dollar loss to the Government for that stratum or universe.
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DETERMINING
EXTRAPOLATION AMOUNT AND VALIDATING THE AUDIT FINDINGS
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It is
necessary to calculate the standard deviation, standard error of
the mean, and sampling error. The contractor shall have the electronic
capability to accomplish these calculations and shall execute the computations
according to the methodology provided in the following paragraphs.
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In the
sample technique discussed in the previous section, if the sample
has been properly designed and selected, and the specific stratum
or universe approximates a normal distribution appropriately, there
are 90 chances in 100 that the claim overpayments will fall within
the range of the arithmetical mean plus or minus 1.645 times the
calculated standard deviation. Additional values shall be calculated as
well, to determine the validity of the overpayment estimates.
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Calculating
the standard deviation of the sample: The standard deviation,
which is expressed in dollars and cents, shall be determined using
the following steps:
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1. Calculate the difference between each claim
observation and the average mean overpayment.
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2. Square each of the calculated differences.
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3. Sum the Squares of the differences for
all of the claim observations.
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4. Divide the Sum of the Squares by the number
of observations in the sample.
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Note: When the sample
size is less than 40, Divide the Sum of the Squares by the number
of observations minus one.
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5. Take the Square Root of the Divided Sum
of the Squares.
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Calculating
the standard error of the mean: The standard error of the
mean shall be calculated by dividing the standard deviation by the
square root of the sample size.
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Calculating
the sampling error and overpayment estimate range: The sampling
error shall be calculated by multiplying the standard error of the
mean by the “Z” score (for a 90% confidence level the “Z” score
is 1.645). The “Z” score changes as the confidence level changes.
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Calculating
the precision value: The precision value, expressed in dollars
and cents, shall be calculated by multiplying the sampling error
by the number of claims in the stratum or universe.
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Calculating
the overpayment estimates: The overpayment point estimate
was calculated above by multiplying the average mean of overpayment
per claim by the number of claims in the specific stratum or universe.
The high and low (plus or minus) estimates of overpayments shall
be calculated respectively by adding and by subtracting the precision
value from the overpayment point estimate. The overpayment estimates
shall be expressed in dollars and cents.
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Calculating
the sample precision percentage: The sample precision percentage
shall be calculated by dividing the precision value by the overpayment
point estimate. The desired precision percentage is 10% or less
for tight precision, with approximately 20% or more representing
low precision.
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Testing the
validity of the sample and the overpayment estimates:
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1. If the standard deviation is greater than
two times the arithmetic mean, this is an indicator that the sample
does not demonstrate the confidence level required for validity.
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2. If the high estimate of overpayments
is greater than the specific stratum or universe amount or the low
estimate of overpayments is less than zero, then the computed overpayment
amount shall not be used.
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3. When high precision is not achieved,
the lower overpayment estimate shall be used as the amount of overpayment
demanded, as opposed to the point estimate. This procedure yields
a conservative demand amount for recovery that is very likely less
than the true amount of overpayment, and it allows a reasonable
recovery without requiring the tight precision that might be needed
to support a demand for the point estimate.
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Alternate Sampling
Methods
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If the
tests for the validity of the sample and overpayment estimates are
not met, it may be an indicator that the universe should have been
stratified appropriately, or other techniques should be used. If
this is the case, consult with DHA PI. For example, if there are
services subjected to audit where there are large differences in
payments (e.g., surgical and medical), there will likely be a need
to stratify the universe into two or more separate categories for
separate sample selection. When stratification is necessary and
after consulting with DHA PI, please seek consultation for such
sample techniques from a qualified statistician.
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The standard
reference for auditing with samples is the Handbook of Sampling
for Auditing and Accounting, Third Edition, by Herbert Arkin, McGraw-Hill
Book Company, copyright 1984.
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