A sample median ratio is 0.87, below the 0.90-1.10 level standard. Under the IAAO Standard on Ratio Studies, what is needed before concluding the jurisdiction fails the level standard?
Correct Answer
A) A confidence interval or hypothesis test
A point estimate outside the range is not enough by itself: noncompliance with appraisal level standards cannot be determined without the use of confidence intervals or hypothesis tests (for example, whether the confidence interval around the median lies entirely below 0.90).
Why This Is the Correct Answer
Option A is correct because, under the IAAO Standard on Ratio Studies, noncompliance with appraisal level standards cannot be determined without the use of confidence intervals or hypothesis tests. A point estimate of 0.87 outside the 0.90 to 1.10 range is not enough by itself. For example, the analyst can check whether the confidence interval around the median lies entirely below 0.90.
Why the Other Options Are Wrong
Option B: A second median from a larger nearby county
Option B, a second median from a larger nearby county, compares a different jurisdiction and does not measure the sampling uncertainty of this sample's 0.87 median. It does not address whether this jurisdiction fails the standard.
Option C: A COD below 10 for the same sample
Option C, a COD below 10 for the same sample, measures uniformity, not appraisal level. A low COD says nothing about whether the median level of 0.87 is statistically below 0.90.
Option D: A weighted mean ratio above 1.00
Option D, a weighted mean ratio above 1.00, is another level measure but does not test whether the median's departure from the standard is statistically significant. It is not the required step.
Point estimate needs a range
A single sample median is a point; to judge failure, wrap it in a confidence interval or test it.
How to use: Use this when a question asks what is needed before declaring a level standard failed.
Exam Tip
Distinguish level (median, mean, weighted mean) from uniformity (COD, PRD); a uniformity measure does not answer a level question.
Common Mistakes to Avoid
- -Declaring failure from a point estimate alone
- -Using a uniformity measure like COD to judge level
- -Comparing to another jurisdiction instead of testing this sample
Concept Deep Dive
Analysis
This question tests the statistical step needed before concluding that a jurisdiction fails an appraisal level standard. A sample median of 0.87 is only a point estimate subject to sampling error. Under the IAAO Standard on Ratio Studies, noncompliance requires a confidence interval or hypothesis test.
Background Knowledge
Ratio study statistics computed from samples are estimates of population values and carry sampling error. Confidence intervals and hypothesis tests quantify that uncertainty. Level standards address central tendency, while uniformity standards address measures such as the COD.
Real-World Application
An oversight agency finds a county's sample median ratio of 0.87 based on a modest number of sales. Before declaring noncompliance, analysts compute a confidence interval around the median to see whether it falls entirely below 0.90.
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