Aresearcher is interested in the effect on test scores of computer usage. using school district data, she regresses district average test scores on the number of computers per student. what are possible sources of bias for β1, the estimated effect on tests scores of increasing the number of computers per student? for each source of bias below, determine whether β1 will be biased up or down.1. average income per capita in the district. if this variable is omitted, it will likely produce a(an) upward or downward bias of the estimated effect on tests scores of increasing the number of computers per student.2. the availability of computerized adaptive learning tools in the district. if this variable is omitted, it will likely produce a(an) upward or downward bias of the estimated effect on tests scores of increasing the number of computers per student.3. the availability of computer-related leisure activities in the district. if this variable is omitted, it will likely produce a(an) upward or downward bias of the estimated effect on tests scores of increasing the number of computers per student.