Traditionally coal has held the distinction of being West Virginia's bedrock industry. With the exception of 1971, West Virginia has lead the nation in coal production consistently since 1931. In recent years many changes have occurred in the coal industry, one of these changes being the relative importance of strip mined coal. In 1960, 6.8 percent of West Virginia's coal was produced by surface mining. By 1971 surface mined coal accounted for 21.9 percent of total production, an increase of 15.1 percentage points. During the same time period the percent of total mining industry employment engaged in surface mining increased from 4.5 to 14.1 percent, an increase of only 9.6 percentage points, indicating the higher relative efficiency of labor in surface mining as compared to underground mining.