Interpret the normal quantile plot. More Info: These data come from earlier edit

Question

Interpret the normal quantile plot.

More Info:

These data come from earlier editions of Introduction to the Practice of Statistics, by David Moore and George McCabe. Studies conducted for the US Agency for International Development (USAID). Wheat-soy blend (WSB) is prepared for emergency food relief. Vitamin C is added to the WSB when it is prepared in the US and shipped overseas for ready availability for disaster relief. There is a concern that vitamin C is lost in shipment and storage.

The researchers selected a simple random sample of 27 bags of freshly-prepared wheat-soy blend at the US preparation site, before shipment to Haiti. They took samples of the WSB, and assessed the Vitamin C content. The bags were specially marked so that they could be resampled 5 months later in Haiti.

The data consist of 27 pairs of measurements. The key variable for analysis is the difference between the factory measurement and the Haiti measurement. We'll create the difference in Stata as the first step in our data analysis. Theoretically, the value of Vitamin C in the Haiti sample can't be any larger than the US value. But because the vitamin C isn't completely uniformly mixed in, and there's some measurement error, so some of the differences might be negative.

The units on the vitamin C measurements are milligrams of vitamin C per 100 grams of WSB.

Explanation / Answer

Given that it is a Q-Q plot of the distribution, we can say with enough
confidence that the plot / distribution is normal.

When the points are almost on the line, we conclude that plot is NORMAL
if the points were fairly away from the line at the ends, we would have said that the distribution is skewed.

PLOT IS NORMAL

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