Chapter 6. Comparing Your Results
2007 Comparative Database Report
To compare your hospital's survey results to the results from the database hospitals, you will need to calculate your hospital's percent positive response on the survey's 42 items and 12 composites (refer to Chapter 5 and the Notes section for a description of how to calculate these percent positive scores). You will then be able to compare your hospital's results against the database averages, and examine the percentile scores to place your hospital's results relative to the distribution of database hospitals.
When comparing your hospital's results against results from the database, keep in mind that the database only provides relative comparisons. Even though your hospital's survey results may be better than the database statistics, you may still believe there is room for improvement in a particular area within your hospital in an absolute sense. As you will notice from the database results, there are some patient safety composites that even the highest-scoring hospitals could improve upon. Therefore, the comparative data provided in this report should be used to supplement your hospital's own efforts toward identifying areas of strength and areas on which to focus patient safety culture improvement efforts.
Description of Comparative Statistics
In addition to the average percent positive scores presented in the charts in the previous chapter (Chapter 5), a number of additional statistics are provided in this report to facilitate comparisons against the database hospitals. A description of each statistic shown in the comparative results tables in this chapter is provided next.
Average Percent Positive and Standard Deviation
The average percent positive scores for each of the 12 patient safety culture composites and for the survey's 42 items are provided in the comparative results tables in this chapter (these statistics were also displayed in the previous chapter in Charts 5-1 and 5-2). These average percent positive scores were calculated by averaging composite-level percent positive scores across all hospitals in the database, as well as averaging item-level percent positive scores across hospitals. Since the percent positive is displayed as an overall average, scores from each hospital are weighted equally in their contribution to the calculation of the average.4
In addition, the standard deviation (SD), a measure of the spread or variability of hospital scores around the average, is also displayed. The standard deviation tells you the extent to which hospitals' scores vary from the average:
- If scores from all hospitals were exactly the same, then the average would represent all their scores perfectly and the standard deviation would be zero.
- If scores from all hospitals were very close to the average, then the standard deviation would be small, and close to zero.
- If scores from many hospitals were very different from the average, then the standard deviation would be a large number.
When the distribution of hospital scores follows a normal, bell-shaped curve (where most of the scores fall in the middle of the distribution, with fewer scores at the lower and higher ends of the distribution), the average, plus or minus the standard deviation, will include about 68 percent of all hospital scores. For example, if an average percent positive score across the database hospitals was 70 percent with a standard deviation of 10 percent (and scores were normally distributed), then about 68 percent of all the database hospitals would have scores between 60 percent and 80 percent.
Statistically significant differences between scores. You may be interested in determining the statistical significance of differences between your scores and the averages in the database, or between scores in various breakout categories (differences in scores by hospital bed size, teaching status, etc). Statistical significance is greatly influenced by samples sizes, so that as the number of observations in comparison groups gets larger, small differences in scores will end up being statistically significant. While a 1 percent difference between percent positive scores might be statistically significant (that is, not due to chance), the difference is not likely to be meaningful or significant in practice. Keep in mind that statistically significant differences are not always important, and nonsignificant differences are not always trivial. Therefore, we recommend the following guideline:
- Use a 5 percent difference as a rule of thumb when comparing your hospital's results to the database averages. Your hospital's percent positive score should be at least 5 percent higher than the database average to be considered "better," and should be at least 5 percent lower to be considered "lower" than the database average. A 5 percent difference is likely to be statistically significant for most hospitals, given the number of responses per hospital, and is also a meaningful difference to consider.
4 As noted in Chapter 5, an alternative method would be to report a straight percent of positive response across all respondents, but this method would give greater weight to respondents from larger hospitals since they account for almost twice as many responses as those from smaller hospitals.
Minimum and Maximum Scores
The minimum (lowest) and maximum (highest) percent positive scores are presented for each composite and item. These scores provide information about the range of percent positive scores obtained by hospitals in the database and are actual scores from the lowest and highest-scoring hospitals. When comparing against the minimum and maximum scores, keep in mind that these scores may represent hospitals that are extreme outliers (indicated by large differences between the minimum and the 10th percentile score, or between the 90th percentile score and the maximum).
The 10th, 25th, 50th (or median), 75th and 90th percentile scores are displayed for the survey composites and items. Percentiles provide information about the distribution of hospital scores. To calculate percentile scores, all hospital percent positive scores were ranked in order from low to high. A specific percentile score shows the percent of hospitals that scored at or below a particular score. For example, the 50th percentile, or median, is the percent positive score where 50 percent of the hospitals scored the same or lower, and 50 percent of the hospitals scored higher. When the distribution of hospital scores follows a normal, bell-shaped curve (where most of the scores fall in the middle of the distribution with fewer scores at the lower and higher ends of the distribution), the 50th percentile, or median, will be very similar to the average score. Interpret the percentile scores as shown in Table 6-1.
To compare against the database percentiles, compare your hospital's percent positive scores against the percentile scores for each composite and item. Look for the highest percentile where your hospital's score is higher than that percentile.
For example: On a survey item, the 75th percentile score is 49 percent positive, and the 90th percentile score is 62 percent positive.
- If your hospital's score on the survey item is 55 percent positive, it falls above the 75th percentile (but below the 90th), meaning that your hospital scored higher than at least 75 percent of the hospitals in the database.
- If your hospital's score on the survey item is 65 percent positive, it falls above the 90th percentile, meaning your hospital scored higher than at least 90 percent of the hospitals in the database.
Composite and Item-level Comparative Tables
Table 6-2 presents comparative statistics (average percent positive and standard deviation, minimum and maximum scores, and percentiles) for each of the 12 patient safety culture composites. The patient safety culture composites are shown in order from the highest average percent positive response to the lowest.
Table 6-3 presents comparative statistics for each of the 42 survey items. The survey items are grouped by the patient safety culture composite they are intended to measure, and within each composite the items are presented in the order in which they appear in the survey.
The comparative results in Tables 6-2 and 6-3 show considerable variability in the range of hospital scores (lowest to highest) across the 12 patient safety culture composites. There was a 69 percent average difference between the percent positive scores of the lowest and highest hospitals for the composites, and a 76 percent average difference for the items. The standard deviation around the average percent positive scores ranged from 6.89 percent to 11.73 percent on the composites, and ranged from 8.42 percent to 14.09 percent on the items.
Patient safety grades shown in Table 6-4 had a wide range of response, from at least one hospital where none of the respondents (0 percent) provided their unit with a patient safety grade of "A-Excellent," to a hospital where 63 percent did.
Number of events reported also had a wide range of response as shown in Table 6-5, from a hospital where 96 percent of respondents had not reported a single event over the past 12 months, to a hospital where only 5 percent had not reported an event.
Highlights of Results in Part II—Appendixes A & B: Results by Hospital and Respondent Characteristics
In addition to the overall results on the database hospitals already presented, the report presents data tables in Appendixes A and B that show average percent positive scores on the survey composites and items across database hospitals, broken down by the following hospital and respondent characteristics:
- Appendix A: Results by Hospital Characteristics
- 1-Bed size.
- 2-Teaching status.
- 3-Ownership and control.
- 4-Geographic region.
- Appendix B: Results by Respondent Characteristics
- 1-Work area/unit.
- 2-Staff position.
- 3-Interaction with patients.
Since there are many breakout tables, they are included in Appendixes A and B. Highlights of the findings from the breakout tables in these appendixes follow.
Highlights from Appendix A: Results by Hospital Characteristics
Bed Size (Table A-1)
Teaching Status, and Ownership and Control (Table A-5)
Region (Table A-9)
Patient Safety Grade (Tables A-3, A-7, A-11)
Number of Events Reported (Tables A-4, A-8, A-12)
Highlights from Appendix B: Results by Respondent Characteristics
Respondent Work Area/Unit (Table B-1)
Respondent Staff Position (Table B-5)
Respondent Interaction With Patients (Table B-9)
Patient Safety Grade (Tables B-3, B-7, B-11)
Number of Events Reported (Tables B-4, B-8, B-12)
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