Completed Diagnosis Worksheet for Evidence-Based General Practice
Citation
Holty I, Forster DP. Evaluation of pure tone audiometry and impedance screening in infant schoolchildren. J Epidemiol Community Health 1992; 46: 21-25.
Are the results of this diagnostic study valid?
-
Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
Yes - the audiometry and tympanometry were done by different examiners 5 days apart and without knowledge of the previous result. -
Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)?
School-aged children were screened. -
Was the reference standard applied regardless of the diagnostic test result?
Yes - all children were supposed to undergo both tests, and 94.1% did.
Are the valid results of this diagnostic study important?
Your calculations:
| Target Disorder (abnormal audiometry) | Totals | |||
|---|---|---|---|---|
| Present | Absent | |||
| Diagnostic Test Result (tympanometry) |
Positive (type B or C) |
99 a |
92 b |
191 a + b |
| Negative (type A) |
73 c |
310 d |
383 c + d |
|
| Totals | a + c 172 |
b + d 402 |
574 |
|
Sensitivity = a/(a+c)
Sensitivity = 99/172
Sensitivity = 58%
Specificity = d/(b+d)
Specificity = 310/402
Specificity = 77%
Likelihood Ratio for a positive test result (LR+) = sens/(1-spec)
Likelihood Ratio for a positive test result (LR+) = 58%/23%
Likelihood Ratio for a positive test result (LR+) = 2.5
Likelihood Ratio for a negative test result (LR-) = (1-sens)/spec
Likelihood Ratio for a negative test result (LR-) = 42%/77%
Likelihood Ratio for a negative test result (LR-) = 0.54
Positive Predictive Value = a/(a+b)
Positive Predictive Value = 99/191
Positive Predictive Value = 52%
Negative Predictive Value = d/(c+d)
Negative Predictive Value = 310/383
Negative Predictive Value = 77%
Pre-test Probability (prevalence) = (a+c)/(a+b+c+d)
Pre-test Probability (prevalence) = 172/574
Pre-test Probability (prevalence) = 81%
Pre-test-odds = prevalence/(1-prevalence)
Pre-test-odds = 30%/70%
Pre-test-odds = 0.43
Post-test odds = Pre-test odds x Likelihood Ratio
Post-test Probability = Post-test odds/(Post-test odds + 1)
Can you apply this valid, important evidence about a diagnostic test in caring for your patient?
-
Is the diagnostic test available, affordable, accurate, and precise in your setting?
Yes. Many practices, including ours, have one of these simple cheap instruments. -
Can you generate a clinically sensible estimate of your patient's pre-test probability (from practice data, from personal experience, from the report itself, or from clinical speculation)
Parental concern is a poor predictor of hearing problems (Rosenfeld, Arch Otolaryngol Head Neck Surg 1998 Sep;124(9):989-92). I would adjust the prevalence slightly to a pre-test value of 40% -
Will the resulting post-test probabilities affect your management and help your patient? (Could it move you across a test-treatment threshold?; Would your patient be a willing partner in carrying it out?)
A positive test would predict about a 63% chance of an abnormal audiogram (and warrant an audiogram); a negative test a 27% chance (and warrant a repeat test in a several weeks). -
Would the consequences of the test help your patient?
Yes - a recent trial (Maw, Lancet 1999 353: 960-3) of delayed versus immediate surgery for OME showed a benefit in language development but that the delayed group also later caught up.
Additional Notes
While the "disease" of interest is otitis media with effusion, I have taken audiometry as the gold standard since it is really the hearing impairment that is important to the child, not the presence of some middle ear fluid.