Stats Lesson 4.1

When we take a census, we attempt to collect data from

• every individual in the population.

• a stratified random sample.

• every individual chosen in a simple random sample.

• a voluntary response sample.

• a convenience sample.

You want to take a simple random sample (SRS) of 50 of the 816 students who live in a dormitory on campus. You label the students 001 to 816 in alphabetical order. In the table of random digits, you read the entries

95592 94007 69769 33547 72450 16632 81194 14873

The first three students in you sample have labels

• 400, 769, 335.

• 955, 929, 400.

• 929,400, 769.

• 400, 769, 769.

• 559, 294, 007

A simple random sample (SRS) is

• a sample that gives every possible sample of the same size the same chance to be selected.

• any sample selected by chance.

• a sample that doesn't involve strata or clusters.

• a sample that is guaranteed to be representative of the population.

Bias in a sampling method is

• any systematic error that tends to occur in the same direction whenever you use this sampling method.

• any error in a sample result, that is, any deviation of the sample result from the truth about the population.

• the random error due to using chance to select a sample.

• any error due to practical difficulties such as contacting the subjects selected

• racism or sexism on the part of those who take the sample.

You want to know the opinions of American high school teachers on the issue of establishing a national proficiency test as a perquisite for graduation. You obtain a list of all high school teacher's belong to the National Education Association and a mail a survey to a random sample of 2500 teachers. In all, 1347 of the reachers return the survey. Of those who responded, 32% say that favor some kind of proficiency test. Which of the following statements is true?

• The results of this survey may be affected by nonresponse bias.

• Since random sampling was used, we can feel confident that the percent of teachers who favor a national proficiency test is close to 32%.

• We cannot trust these results, because the survey was mailed. Only survey results from face-to-face interviews are considered valid.

• Because over half of those who were mailed responded, we are confident that 32% of all teachers favor a proficiency test.

• The results of this survey cannot be trusted due to voluntary response bias.