The International Adult Literacy Survey25 was a 22-

country study in which nationally representative samples of adults were interviewed and tested at home, using the same literacy test having scores that could range from 0 to 500. For those of age 16–25, some of the mean prose literacy scores were United Kingdom 273.5, New Zealand 276.8, Ireland 277.7, United States 277.9, Denmark 283.4, Australia 283.6, Canada 286.9, the Netherlands 293.5, Norway 300.4, and Sweden 312.1.

The website does not provide sample sizes or standard deviations. Suppose each sample size was 250 and each standard deviation was 50.

How far apart do two sample means have to be before you feel confident that an actual difference exists between the population means? Explain your reasoning, giving your conclusion for Canada and the United States.