Info_ntrade.md
In qPRAentry: Quantitative Pest Risk Assessment at the Entry Step

output: html_document: default pdf_document: default

Overview of $N_{trade}$ Shiny app

$N_{trade}$ is defined as "the potentially infected/infested quantity of commodities imported by a country from third countries where the pest is present".

This application is meant to calculate $N_{trade}$ for countries included in the NUTS (Nomenclature of territorial units for statistics) coding system, which includes European Union Member States, EFTA countries, candidate countries and potential candidates. Note that it is not necessary to consider all countries included in this list.

For other countries worldwide, the calculation of $N_{trade}$ can be performed using the ntrade function from the qPRAentry package.

For the use of this application, trade data of the commodities of interest, i.e., potential carriers of the pests under assessment, are required. The required trade data are:

$ExtraTotal Import$: Total quantity of commodity from third countries imported by the countries of interest.
$ExtraPest Import$: Quantity of commodity from third countries where the pest under assessment is present, imported by the countries of interest.
$Intra Trade$: Quantity of commodity traded between the countries of interest.
$Internal Production$: Quantity of commodity produced in the countries of interest.

All the trade data required can be accessed through the Eurostat database.

For a given country $i$, $N_{trade_i}$ is calculated taking into account the quantity of commodity imported by country $i$ from third countries where the pest is present, and the internal trade of this commodity, i.e., export and import between country $i$ and other countries $j$, with $j \neq i$. Thus, $N_{trade_i}$ is approached as:

$$ N_{trade_i} = ExtraPest_i - ExtraPest_i \sum_{j \neq i} R_{ij} + \sum_{j \neq i} ExtraPest_j R_{ji}, $$

where $ExtraPest_i$ and $ExtraPest_j$ are the quantity of commodity imported from third countries where the pest is present by country $i$ and country $j$, respectively. $R_{ij}$ and $R_{ji}$ represent the proportion of commodity exported from $i$ to $j$ ($IntraExp_{ij}$), and from $j$ to $i$ ($IntraExp_{ji}$), respectively, out of the total available commodity in the exporter country. This total quantity is considered as the sum of the internal production of the country ($IP$) and the total quantity imported from third countries ($ExtraTotal$), regardless of whether the pest is present. Thus, $R_{ij}$ and $R_{ji}$ are defined as:

$$R_{ij} = \frac{IntraExp_{ij}}{IP_i + ExtraTotal_i},$$ $$R_{ji} = \frac{IntraExp_{ji}}{IP_j + ExtraTotal_j}.$$

Based on these proportions, the quantity of $ExtraPest_i$ re-exported from country $i$ to all countries $j$ is approximated by $ExtraPest_i \sum_{j \neq i} R_{ij}$, and the quantity of $ExtraPest_j$ re-exported from all countries $j$ to country $i$ as $\sum_{j \neq i} ExtraPest_j R_{ji}$.

After calculating $N_{trade}$ at the national level (NUTS0), the next step involves redistributing these quantities to NUTS2 regions.

Users have two options for redistributing $N_{trade}$ data to NUTS2 regions:

Human population-based redistribution using Eurostat data
Overview: This option allows users to redistribute $N_{trade}$ data to NUTS2 regions proportionally based on human population data. The human population data is sourced from Eurostat and is already integrated into the application.
How it works: The $N_{trade_i}$ value for a country $i$ is redistributed to its respective NUTS2 regions $k$. This redistribution is done proportionally based on the human population of each region $k$. Thus, the quantity allocated to a specific region $k$ is calculated as $N_{trade_k} = N_{trade_i} \cdot (Population_k / Population_i)$.
Custom redistribution using user-uploaded data
Overview: This option provides users with the flexibility to perform a personalised redistribution based on custom data. Users can upload their own data frame containing specific values for each NUTS2 region.
How it works: Users upload a file containing the NUTS2 codes along with the corresponding values from which $N_{trade}$ will be proportionally redistributed (e.g., consumption data). The application will then use this custom data frame to redistribute the $N_{trade_i}$ value for a country $i$ to its respective NUTS2 regions $k$ proportionally according to the value of each region $k$. Thus, the redistributed quantity for each region $k$ is calculated as $N_{trade_k} = N_{trade_i} \cdot (Value_k / Value_i)$.

Upon completion of the analysis, the user will have the option to download a ZIP file containing:

A comprehensive report summarising the analysis results (Ntrade_report.html)
A CSV file with the $N_{trade}$ table results at NUTS0 level (Ntrade_NUTS0.csv)
A CSV file with the $N_{trade}$ table redistribution results at NUTS2 level (Ntrade_NUTS2.csv)

To proceed with the analysis, navigate to the $N_{trade}$ tab at the top of the page.