Your graph does not seem to show a straight correlation between increasing minimum wage as a fraction of average hourly wage and UNEMPLOYMENT FOR WORKERS WITH LESS THAN A HIGH SCHOOL EDUCATION.
Why is it showing a downward trend when it reaches 0.4 or a little above 0.38 ?
I would expect it to be either linear (going up) but it clearly isn't.
Why is it showing a downward trend when it reaches 0.4 or a little above 0.38 ?
I don't think it does show such a trend. While there might be a couple of outliers, the overall trend is clear. Those couple of lowest points, outliers on the graph, are for the years 1999 and 2000 -- the best unemployment figures since 1970.
And I don't think we expect the trend to be completely linear. If the minimum wage is below the equilibrium price for low-skill workers, then it will tend to have little effect. It's only as the minimum wage exceeds this price that you get increases in unemployment. So we would expect the graph to first look a bit like a horizontal line followed by a line that slopes upward.