At its website (www.gallup.com) the Gallup World Poll reports results of surveys conducted in various places around the world. At the end of one of these reports about the reliability of electric power in Africa, they describe their methods, including explanations such as the following: Results are based on face-to-face interviews with 1,000 adults, aged 15 and older, conducted in 2010 in Botswana, Burkina Faso, Cameroon, Central African Republic, Chad, Ghana, Kenya, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone, South Africa, Tanzania, Uganda, and Zimbabwe. For results based on the total sample of national adults, one can say with 95% confidence that the maximum margin of sampling error ranges from, ± 3.4 percentage points to +4.0 percentage points. The margin of error reflects the influence of data weighting. In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.
a) Gallup is interested in the opinions of Africans. What kind of survey design are they using?
b) Some of the countries surveyed have large populations. (South Africa is estimated to have over 50 million people.) Some are quite small. (Zimbabwe has fewer than 13,000,000 people.) Nonetheless, Gallup sampled 1000 adults in each country. How does this affect the precision of its estimates for these countries?