There are two main categories of unemployment: natural rate and cyclical. Natural rate is the minimum level that exists even during economic booms, while cyclical unemployment rises and falls with the business cycle. Unemployment is measured monthly through surveys by the Bureau of Labor Statistics, though it has limitations. Most spells of unemployment are short-term, while long-term unemployment accounts for most joblessness at a given time. Reasons for unemployment include the natural time it takes to search for a job, as well as factors like minimum wages and unions that can disrupt the labor market's supply and demand balance.