12-5 Samples and Surveys

Quantitative: data measure quantities and can be described numerically Example: test scores, ages, time, weight Qualitative: data name qualities and can be words or numbers Example: Sports, zip codes, hair color

Problem 1: Classifying Data Is each set Qualitative or Quantitative? Favorite Movies Number of students in different school who take Spanish Football Jersey Numbers

Univariate: a set of data that uses only one variable Bivariate: a set of data that uses two variables

Problem 2: Identifying Types of Data Is each data set univariate or bivariate? The atomic weights of the elements in the periodic table The edge lengths and volumes of cubes Heights and weights of mammals The cost of Internet service from several different providers

Populations: the entire group that you want information about Sample: When a population is too large to survey, statisticians survey a part of it to find characteristics of the whole. This part is called the Sample

NAME SAMPLING METHOD EXAMPLE Random Survey a population at random Survey people whose names are drawn from a hat Systematic Select a number n at random. Then survey the nth person Select the number 5 at random. Survey every fifth person Stratified Separate a population into smaller groups, each with a certain characteristic. Then survey at random within each group. Separate a high school into 4 groups by grade level. Survey a random sample of students from each grade

Problem 3: Choosing a Sample You want to find how many DVDs students at your school rent in a month. You interview every tenth teenager you see at a mall. What sampling method are you using? Is this a good sample

You revise your plan and interview all students leaving a school assembly who are wearing the school colors. Will this plan give a good sample? Explain.

BIAS: when a survey contains assumptions that may or may not be true BIAS: when a survey contains assumptions that may or may not be true. It can influence opinion and can make one answer seem better than another.

Problem 4: Determining Bias in a Survey A reporter wants to find out what kinds of movies are most popular with local residents. The reporter asks “Do you prefer exciting action movies or boring documentaries?” Is the question biased? Explain.