Bivariate data often arises from the use of two different techniques to measure the same quantity. As an example, the accompanying observations on x = hydrogen concentration1
(ppm) using a gas chromatography method and y = concentration using a new sensor method were read from a graph in the article "A New Method to Measure the Diffusible Hydrogen Content in Steel Weldments Using a Polymer Electrolyte-Based Hydrogen Sensor" (Welding Res., July 1997: 251s-256s).

Construct a scatter-plot. Does there appear to be a very strong relationship between the two types of concentration measurements? Do the two methods appear to be measuring roughly the same quantity? Explain your reasoning.

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x | 47 62 65 70 70 78 95 100 114 118 y 38 62 53 67 84 79 93 106 117 116 x 1124 127 140 140 140 150 152 164 198 221 127 114 134 139 142 170 149 154 200 215