Answer to Question 1
Across the decades, the government has used different classifications systems to categorize people such that the same individual could, over the course of a lifetime, fall into different categories. In addition, some groups are categorized into groups on the basis of illogical rules, such as the one drop rule that people use: one drop of black blood makes one black, but one drop of white blood doesn't make one white. Further, some categories (e.g., Hispanic) are used to indicate race in certain circumstances but not in others. Finally, the genetic differences across the so-called races do not reliably distinguish people in different groups. There may be patterns, but there are people who don't easily fall into a given category.
Answer to Question 2
Measurement error does not indicate that a researcher has made an error. It means that the data do not perfectly represent the concept of interest. Instead, measurement error reflects the effect on a measurement of some variable that is not of interest in the research. It may reflect poor wording on a questionnaire, temporary inattention by the participant, or a multitude of other factors unrelated to the research.
Discipline-specific training can take years to perfect.
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