From reh0303@hub.doh.wa.gov Tue Jun 16 10:40:20 1998 Received: from mxu3.u.washington.edu (mxu3.u.washington.edu [140.142.33.7]) by lists.u.washington.edu (8.8.4+UW97.07/8.8.4+UW97.05) with ESMTP id KAA36064 for ; Tue, 16 Jun 1998 10:40:19 -0700 Received: from smtp.hub.doh.wa.gov (hub.doh.wa.gov [192.230.1.5]) by mxu3.u.washington.edu (8.8.4+UW97.07/8.8.4+UW97.09) with SMTP id KAA01605 for ; Tue, 16 Jun 1998 10:40:16 -0700 Received: from Connect2 Message Router by smtp.hub.doh.wa.gov via Connect2-SMTP 4.00; Tue, 16 Jun 98 10:42:42 -0700 Message-ID: In-Reply-To: Date: Tue, 16 Jun 98 10:40:24 -0700 From: "Hoskins, Richard E." Sender: "Hoskins, Richard E." To: waphgis@u.washington.edu Subject: RE: Census data for assessment X-mailer: Connect2-SMTP 4.00 MHS to SMTP Gateway Dr Rarig's comments are really on the mark, and especially " state the source for the denominator so readers can make their own judgments about how that affects the output." I would add that for rate calculations for inference it is important to calculate a confidence interval; most formulas for which assume that the denominator has no variance which is clearly not true. Any CI you calculate would be wider if the variance of the denominator were taken into account. It is tempting to calculate a disease rate in a county for several years and then look at the confidence interval overlap to get some idea about statistically significant change from one year to the next or even just compare with a regional or state value - but if the population model supplies no estimate of the variability of the population estimate these trends will not be possible to detect or quantify. And if the numbers are small anyway ... I wonder if it might be best to just display count data on maps and leave it at that .. forget rates. Richard E. Hoskins, PhD MPH WA State Public Health Geographer GIS and Spatial Epidemiology Office of Epidemiology WA State Department of Health 1102 Quince St, Olympia, WA 98504-7812 eMAIL: REH0303@hub.doh.wa.gov tel: 360-236-4270 fax:360-236-4245 .