## Travellers in

The travellers in indicator estimates the number of people who visited an area after having visited any other area during the same time period. This indicator only counts each unique subscriber once, unlike the trips in indicator which could include multiple trips into an area by the same subscriber.

The usual resolution for this indicator is:

• Temporal: daily

This indicator can be used to monitor the variation in the number of unique individuals travelling to an area from other locations over time.

Calculation

We calculate the travellers in indicator from the count of travellers aggregate as the sum of the counts of unique subscribers who were present in any other area after being present in an area of interest during a given period of time.

We can adjust the estimated number of subscribers travelling into an area with respect to the changes in the number of active subscribers in the area of interest.

We can also convert the indicator from the number of subscribers to the number of people between areas using a static population figure, such as that produced by a census. We may also adjust the indicator for representation biases based on mobility errors estimated from survey data.

## Travellers out

The travellers out indicator estimates the number of people who visited the area before visiting any other area during the same time period. This indicator only counts each unique subscriber once, unlike the trips in indicator which could include multiple trips into an area by the same subscriber.

The usual resolution for this indicator is:

• Temporal: daily

This indicator can be used to monitor the variation in the number of unique individuals travelling to other locations from an area over time.

Calculation

We calculate the travellers in indicator from the count of travellers aggregate as the sum of the counts of unique subscribers who were present in any other area before being present in an area of interest during a given period of time.

We can adjust the estimated number of subscribers travelling out of an area with respect to the changes in the number of active subscribers in the area of interest.

We can also convert the indicator from the number of subscribers to the number of people between areas using a static population figure, such as that produced by a census. We may also adjust the indicator for representation biases based on mobility errors estimated from survey data.

## Travellers

The travellers indicator estimates the number of people who visited area B after visiting area A during a given period of time.

The usual resolution for this indicator is:

• Temporal: daily

We can use this indicator to monitor the variation in the number of people travelling between pairs of locations.

Calculation

We calculate the travellers indicator using the count of travellers indicator from the directed number of trips between areas.

For a given pair of areas, we estimate the number of travellers who travelled from area A to area B as the unredacted count of subscribers who are present in area B after being present in area B during a given period of time.

We can adjust the estimated number of subscribers travelling between areas with respect to the changes in the number of active subscribers in the area of interest.

We can also convert the indicator from the number of subscribers to the number of people between areas using a static population figure, such as that produced by a census. We may also adjust the indicator for representation biases based on mobility errors estimated from survey data.

## Travellers difference

The travellers difference indicator estimates the change in the number of travellers moving between areas A and B during a period of time compared to the baseline number of travellers during a reference period. If the number of people present in the area has increased, the indicator will have a positive value; if the number has decreased, the value will be negative.

The usual resolution for this indicator is:

• Temporal: daily

This indicator can be used to determine the change in the number of people in a given area over time.

Calculation

We calculate the travellers difference indicator using the count of travellers aggregate and the baseline number of travellers between the areas during a reference period. The baseline can be calculated using the count of travellers aggregate, for example by calculating the median number of travellers during the reference period.

We estimate the change in the number of travellers between pairs of locations by deriving the number of travellers for the period of interest from the count of travellers aggregate as described above. We then subtract the baseline number of travellers from the number of travellers during the period of time of interest.

We can adjust the estimated number of subscribers travelling between areas with respect to the changes in the number of active subscribers in the area of interest.

We can also convert the indicator from the number of subscribers to the number of people between areas using a static population figure, such as that produced by a census. We may also adjust the indicator for representation biases based on mobility errors estimated from survey data.

## Percent change in travellers difference

The percentage change in travellers indicator estimates the change in number of travellers moving between areas A and B during a period of time relative to the baseline number of residents in the reference period. The difference is expressed as a percentage of a baseline value calculated for the reference period. If the number of travellers has increased, the indicator will have a positive value; if the number has decreased, the value will be negative.

The usual resolution for this indicator is:

• Temporal: daily

This indicator describes the change in the number of travellers between pairs of areas, relative to a baseline number of travellers during a reference period.

Calculation

We calculate the difference in the number of travellers relative to the baseline as described above. We divide this difference by the baseline number of travellers during the reference period and multiply by 100 to derive the percentage change.

We can adjust the estimated number of subscribers travelling between areas with respect to the changes in the number of active subscribers in the area of interest.

We can also convert the indicator from the number of subscribers to the number of people between areas using a static population figure, such as that produced by a census. We may also adjust the indicator for representation biases based on mobility errors estimated from survey data.

## Abnormality

The travellers abnormality indicator measures the deviation of the number of travellers moving between areas A and B during a period of time relative to a reference period, expressed as a z-score. A positive value for this indicator greater than 3 indicates a statistically significant increase in the number of travellers; a value less than -3 indicates a statistically significant decrease.

The usual resolution for this indicator is:

• Temporal: daily

This indicator describes how unusual the number of travellers from area A to area B is, given the amount of variation observed during the reference period. Higher absolute values indicate greater deviation from the normal variation in travellers, and therefore greater probability that the change is meaningful. Such changes may be associated with specific events or may be caused by technical issues. Very large abnormalities (absolute values greater than 6) may, however, be more indicative of a technical issue.

Calculation

## Abnormality

The trips abnormality indicator measures the deviation of the number of travellers moving between areas A and B during a period of time relative to a reference period, expressed as a z-score. A positive value for this indicator greater than 3 indicates a statistically significant increase in the number of travellers; a value less than -3 indicates a statistically significant decrease.

The usual resolution for this indicator is:

• Temporal: daily