Basic Data Interpretation

Most data-interpretation questions test a single skill: reading a value off a chart accurately. To find the value of the graph at a particular input, trace up from that point on the horizontal axis to the curve, then straight across to the vertical axis.

In the figure, to read the value at $x = 3$ you go up to the curve and across, landing at a $y$ of about $5$. The same approach reads the coordinates of marked points: a point on the $y$-axis has $x = 0$, and a point on the $x$-axis has $y = 0$.

Trends and extremes are read the same way: an upward-sloping graph shows an increasing quantity and a downward slope a decreasing one, while the highest and lowest points give the maximum and minimum.

Charts come in several forms, but the locate-and-read method is the same. A bar graph shows each value as the height of a bar, so reading it means comparing heights or finding the tallest or shortest.

A dot plot stacks one dot per data point above each value, so the height of a stack is its frequency; counting dots gives totals and helps locate the median.

A scatterplot shows individual data points, and a line of best fit is the straight line that best follows their overall trend. The line need not pass through every point: predictions are read from the line, not from the scattered dots.

A line graph plots cups of coffee against the hour. To find the value at hour $14$, go up from $x = 14$ to the line and across to the vertical axis: the $y$-coordinate is $45$, so $45$ cups.

A line crosses the $y$-axis at one point and the $x$-axis at another. The point on the $y$-axis must have $x = 0$, so it is $(0, 4)$; the point on the $x$-axis must have $y = 0$, so it is $(2, 0)$.

A line of best fit is drawn through a scatterplot. To find which points lie on it, read the line itself, not the data: here the line passes through $(0, 48)$, $(2, 70)$, and $(6, 114)$. The point $(3, 80)$ is a data point but sits just off the line, so it is not on the line of best fit.