Title:
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Extending Scottish exception reporting systems spatially and temporally
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Title: ‘Extending Scottish Exception Reporting Systems Spatially and Temporally’
Abstract: Exception reporting systems allow medical conditions and micro-organisms
to be automatically monitored for unusually high levels. Typically, statistical
models are used to predict expected levels. Where observed levels
exceed the predicted ones by some pre-determined amount, an ‘exception’
is reported to give warning. We focus on developing suitable models for use
in the predictive component of such systems.
Two particular systems are extended spatially to monitor counts at the regional
health board level. The first of these uses call data from the 24-hour
medical helpline NHS24, to monitor particular medical syndromes. The
second uses counts of positive lab identifications of micro-organisms collected
by Health Protection Scotland (HPS). Regional incidences tend to
have very small counts, and for these, we use negative binomial Generalized
Linear Models (GLMs). However, GLMs assume that observations are
independent, which is rarely, if ever, the case in the systems we consider.
Two approaches are investigated for dealing with serial correlation and capturing
local trend, both of which improve the models. We also investigate
links between the health boards and investigate if these links can be used
to further improve the models.
A new system is produced for monitoring daily all-cause mortality in Scotland,
using data collated by the General Register Office. Fitting models to
this data is challenging because of the sharp peaks present in the annual
seasonality; to address this, we use Generalized Additive Modelling. There
is also a marked delay in the reporting of deaths, which must be dealt with
if the system is to detect unusually high levels of mortality in a timely fashion.
We present a straight forward ‘correction’ to do this. Combining these
elements, a mortality surveillance system is produced, which has been used
by HPS to monitor mortality during the swine flu pandemic (2009).
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