In previous years, the average market price of warehouses in a particular city equated to $322.80 per m² of usable floor space. An investor wants to determine whether this figure has changed. A researcher is hired who randomly samples 19 warehouses that are for sale in the city and finds that the mean price is $316.70 per m² of usable floor space with a standard deviation of $12.90 per m². If the researcher uses a 5% level of significance, what statistical conclusion can be reached?