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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