2. Sampling Error

3. Discuss The number of people living with HIV in South-Saharan Africa in 2006 was 24.7 million According to the AIDS Epidemic Update: special report on HIV/AIDS by UNAIDS, December 2006 http://data.unaids.org/pub/EpiReport/2006/2006_EpiUpdate_en.pdfhttp://data.unaids.org/pub/EpiReport/2006/2006_EpiUpdate_en.pdf accessed September 2007

4. 24.7 million

9. Precision We know that the estimates will be subject to sampling error because: Not all the population is included in the study and different samples will give different estimates

10. The problem… We only have one shot! So we need to make the best of it and more importantly we need to know how close to the true target we get our estimate

11. BIAS

12. Bias Errors that occur systematically BIAS