Firms therefore need to put in some effort to know whom they are hiring. In the case of more highly paid workers, this means they spend time and money on interviews, tests, references, and so forth. This is costly both for the firms and the workers, and seems to be universal. In Ethiopia, a study found that just applying for a midlevel clerical job took several days and repeated journeys. Each application cost the would be applicant a tenth of the monthly wage he would earn and had a very low probability of leading to a hire, one reason why few people applied. For this reason, in the case of lower-paid workers, firms often skip the interview and rely on the recommendation of someone they trust. Relatively few firms hire those who just walk in and ask for a job, even if they say they would accept a lower wage. This of course flies in the face of the standard supply-demand framework. But it is too costly to be put in a position where the employer might want to get rid of a worker. In a striking example, researchers trying to find firms in Ethiopia willing to randomize whom they hired, approached over three hundred firms before they found five that were willing to join the experiment. These were jobs where no specific skills were needed, but the firms still wanted to retain some control over whom they hired. Evidence from other studies in Ethiopia suggests percent of firms insist on work experience even for blue-collar jobs, and it is also common to ask for a referral from an employer.