Question 7: The authors say that 'False positives occurred with a frequency of 7.0% and false negatives 3.8%.' What have they done to get these numbers?
| Urine Gram stain | UTI | Total | |
|---|---|---|---|
| Positive | Negative | ||
| Positive | 50 | 3 | 53 |
| Negative | 2 | 40 | 42 |
| Total | 52 | 43 | 95 |
The authors have obtained the 'frequency of false positives' by subtracting the specificity from 100% (100.0 - 93.0 = 7.0). They have obtained the 'frequency of false negatives' by subtracting the sensitivity from 100% (100.0 - 96.2 = 3.8).
To confirm this, there are six posible proportions they could have used from this table:
3/53 = 5.7%
3/43 = 7.0%
3/95 = 3.2%
2/42 = 4.8%
2/52 = 3.8%
2/95 = 2.1%
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Last updated: 1 March, 2007.