Before revision:  However, for TQ to be effective, it has has to be based on contact tracing and the ratio of tests/ per day to the number of new cases/ per day has to be scaled with the mean number of contacts that an infectious person has , which would be high in regions with high population density and low levels of social distancing .
After revision:  However, for TQ to be effective, it has has to be based on contact tracing and the ratio of tests/ per day to the number of new cases/ per day has to be scaled with the mean number of contacts that an infectious person has , which would be high in densely populated regions with low levels of social distancing .