4. the u. s. bureau of labor statistics (bls) wishes to estimate the fraction of individuals who belong to a labor union. they are considering two methods of sampling. for each method, explain if you think it will be subject to selection bias (yes or no) and why, and if it will be subject to non-response bias (yes or no) and why. also state whether you think each method will result in too small (downward bias) or too large (upward bias) an estimate of the true average. a)bls will call a random sample of phone numbers from each town and city’s phone book during regular business hours (9 am to 5 pm) and ask whether or not the person who answers belongs to a union. b)bls will survey people at the entrance of each factory in the country on weekday mornings and ask them if they belong to a union. c)now propose a sampling method of your own that you think will generate a more accurate national average. explain why you think it is better.