Public health interventions
---------------------------

In line with the OECD framework :cite:p:`Sassi2008`, public health policies to tackle 
key risk factors for population health and to promote healthier lifestyles can be categorised in the 
following four broad groups: 

 * policies influencing lifestyles through information and education
 * policies widening the set of healthy choice options
 * policies modifying the opportunity cost of health-related choices
 * policies regulating or restricting actions promoting unhealthy choice options.

Dimensions used to model policy interventions
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Whether a particular policy will work in a given context depends on a number of factors, some of which 
can be location-specific. For example, the return of investment of a policy may depend not only on its 
general efficacy, but also on the local medical costs of treating related diseases and complications; 
demographic structure; epidemiological burden and the cost of intervention implementation. Within 
the model, policies are modelled with respect to the following four key parameters:

 * **Effectiveness of interventions at the individual level**: This parameter captures how individual behaviour changes, following exposure to the interventions. As much as possible, this evidence is borrowed from peer-reviewed meta-analyses, preferably of randomised control trials. 
 * **Time to the maximum effectiveness achieved and effectiveness over time**: The effects of an intervention can be time-limited and/or time-dependant, with the relationship generally at first becoming stronger, and then fading out. This parameter describes changes in the effectiveness of interventions over time. 
 * **Intervention coverage, including description of eligible populations, as well as their exposure**: For example, some interventions may only affect a subset of a population (e.g., individuals in certain age groups or with particular risk factors). In addition, in some cases, only a proportion of the eligible population may be exposed, such as only those who visit primary care and are willing to participate. 
 * **Implementation cost**: The implementation of a public health action may entail a number of costs including, for example, costs related to planning, administration, monitoring and evaluation. In addition, interventions may involve providing some form of equipment or material to be delivered to the target population (e.g. brochures, or stand-up desks). The intervention costs are estimated based on the WHO-Choice methodology (:cite:p:`Tan-Torres2003`) taking into account differentials in relative prices (as measured by differences in PPPs and exchange rates). All costs are expressed in 2017 USD PPPs.

Specific interventions used by the model 
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To date, the SPHeP-NCD model has been used to model a limited number of interventions which address unhealthy diet, 
physical inactivity, overweight, as well as harmful alcohol consumption. More interventions will be added to the model as the field
developed.

Specific details on how each of the interventions in :numref:`interventions` are modelled can be found in 
:numref:`specific_int`. 

.. _interventions:
.. csv-table:: Policy interventions in public health
   :file: Interventions2.csv
   :header-rows: 0
   :stub-columns: 0
   :widths: 20, 100, 100, 100


The following links provide previous intervention modelling studies using the SPHeP-NCD model: 

* The impact of `public transport <https://www.sciencedirect.com/science/article/pii/S0749379718323663?via%3Dihub>`_ on physical activity.
* The impact of `primary care intervention <https://onlinelibrary.wiley.com/doi/full/10.1111/obr.12654>`_ promoting physical activity on becoming. 


.. [#f1] Distribution of nutritional education materials and provision of healthy foods. This intervention is modelled together with School-based programmes for physical activity. 
.. [#f2] Inclusion of physical activity in school curricula. 
.. [#f3] E.g. standing work stations and treadmill desks