How can city planners ensure they are diagnosing urban problems, such as blight, correctly? Implementing solutions based on a wrong diagnosis harms residents and business. One way to avoid a wrong diagnosis is to base the diagnosis on knowledge already on record about the problems.
There are two dictionary definitions of diagnosis but each definition leads to a different decision model for diagnosing problems, causes and solutions.
In the first definition, diagnosis is defined as the analysis of the cause(s) or nature of a problem.
This model is often used by city planners to diagnose problems such as urban blight. Undesirable phenomena (such as physical deterioration of buildings or neighborhoods) are identified as problems and the possible causes are then analysed. Solutions are designed to influence the causes. Published data is also used to describe the problems and validate solutions.
But these undesirable phenomena are often subjective and personal observations; in some studies they have been identified as blight. There may also be multiple causes of these observations ranging from neglect to lack of maintenance and these causes have also been labelled as blight as well. Studies have indicated that a diagnosis of observations and their likely causes will be speculative and based on assumptions.
In the second definition, diagnosis is defined as the act of identifying a health problem, specifically a disease or an illness, based on prior knowledge of the problem. The medical decision model depends on recorded knowledge to diagnose health problems and has been successfully used, discussed and tested by physicians throughout the world for centuries.
The simple idea behind this model is that recorded knowledge about a problem is necessary before it can be identified.
If this medical model is applied to diagnosing problems in cities it will be to identify problems based on recorded knowledge. This knowledge is gained from professional training about the structure and functioning of cities and from published updates from recognized sources.
The point of this model is that the practitioner, whether a physician or a city planner, must have recorded knowledge about a problem, its causes and its solution before it can be diagnosed.
Recorded knowledge about problems, causes and solutions is required whether health problems such as diseases or urban problems such as blight are be diagnosed correctly. If there is limited or no knowledge about a problem it can not be diagnosed, even if the observations are considered undesirable.The same applies to causes and solutions.
While published data is essential for diagnosing problems in the medical model it is optional in the model based on identifying causes where it is often used to describe observations and/or their causes or to validate conclusions.
There are therefore very good reasons for city planners to use the medical decision model when diagnosing urban problems to ensure that their diagnosis is correct.
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