The information provided on the site enables the user to
calculate confidence intervals for each reported measure.
Confidence intervals can be used to estimate the precision
of the calculated rates for an individual hospital. A confidence interval is the
range of values, within which an estimated value or rate is likely to fall. A
confidence interval is a statistical determination of the degree of certainty
associated with an estimated value. As can be seen in the table of estimated
values (below), large differences between individual hospitals’ rates may be
significant, and small differences between hospitals are usually not
significant.
The smaller the sample size, the greater the difference in
rates must be order for that difference to be statistically meaningful. Also, as
sample size varies between hospitals, it is difficult to precisely compare their
rates, without considering the confidence intervals.
Over time, as the quality data base is expanded, a full
four quarters of data will be posted for each measure. The number of cases used
to determine hospitals' rates will likely increase, thereby increasing the
reliability and stability of the rates.
| Estimating Confidence Intervals for the Process of Care Measures:
Estimated Values for Proportion Data |
| |
10% |
20% |
30% |
40% |
50% |
60% |
70% |
80% |
90% |
| <25 |
-- |
-- |
24.9% |
26.6% |
27.2% |
26.6% |
24.9% |
-- |
-- |
|
25-75 |
8.3% |
11.1% |
12.7% |
13.6% |
13.9% |
13.6% |
12.7% |
11.1% |
8.3% |
|
76-125 |
5.9% |
7.8% |
9.0% |
9.6% |
9.8% |
9.6% |
9.0% |
7.8% |
5.9% |
|
126-175 |
4.8% |
6.4% |
7.3% |
7.8% |
8.0% |
7.8% |
7.3% |
6.4% |
4.8% |
|
176-225 |
4.2% |
5.5% |
6.4% |
6.8% |
6.9% |
6.8% |
6.4% |
5.5% |
4.2% |
|
226-275 |
3.7% |
5.0% |
5.7% |
6.1% |
6.2% |
6.1% |
5.7% |
5.0% |
3.7% |
|
276+ |
2.9% |
3.9% |
4.5% |
4.8% |
4.9% |
4.8% |
4.5% |
3.9% |
2.9% |
|
Source: CMS/OCSQ/QIG: The values in the table are the approximate amount to add
and subtract from the observed rate to estimate a 95 percent confidence interval
for the given sample size. (Interpolation between the values in the table is
appropriate.) Estimates of an interval in these cells exceed the natural limits
for proportions.
|