CS6603 Exercise 1 Solution

When you are given scientific information, it is important to be able  to evaluate if the information is accurate. You can investigate the accuracy of scientific information by evaluating whether the conclusions presented are justified based on the experimental design used to collect data. In today’s activities you will practice identifying sources of bias introduced by different experimental designs.

In Part 1, you will be presented with six studies, all which make different claims about the rate of teenage smoking. First, carefully read each study and the results from each study. Next, report an aspect of the experimental design that might bias the results. Following this, determine if the bias you have identified is sampling bias (testing unrepresentative sample, not taking a random sample, or taking too small a sample) or measurement error. Finally, write two sentences explaining the possible affects of the bias on the results (e.g. overestimation or underestimation of teenage smoking). In Part 2, you will be asked to design your own experiment to determine the rate of teenage smoking.

PART 1: Evaluating different experimental designs

Source of Bias: Looking only at the smoking parking lot.

Type of Bias: Sampling bias

Affects of Bias on Results: Since Dr. Jackson is only looking at the smoking parking lot, the rate of teenage smoking assessed from this sample will not be representative of the population of teenagers; and will most likely be higher than the smoking rate of all teenagers.








Source of Bias: Having the parents in the room

Type of Bias: Measurement bias

Affects of Bias on Results: Few students will admit in front of their parents that they smoke so there will likely be an underestimation of the teenage smoking rate.






Source of Bias: Sampling a teenage hangout and students selected by the principal

Type of Bias: Sampling bias



Source of Bias: Requiring the permission slips to be returned to be able to sample

Type of Bias: Sampling bias








Source of Bias: Students only monitored from 3-5 pm and at parties.

Type of Bias: Measurement bias


Experiment 6: A citizen’s group, No Butts, has passed around a petition that will make it illegal to have billboard cigarette advertisements in their city. The group claims that billboard cigarette advertisements are often geared at teenagers and that these billboards cause increased smoking rates among teens. The Dancing Frog Cigarette Company claims that their advertising is not aimed at teenagers and that restricting their advertising will have no effect on the rate of teenage smoking. To demonstrate their point, Dancing Frog Cigarette Company hires Dr. Crabtree to conduct a study comparing the smoking rate at schools in towns with cigarette billboard advertising and schools in towns without cigarette billboard advertising. Dr. Crabtree goes to three freshman classrooms in areas with and without advertising. These areas are approximately 5 miles apart. Dr. Crabtree asks the students to raise their hands if they would answer “yes” to the following questions: Have you ever smoked? Do you smoke everyday? Do you smoke once a month or more? The following data was recorded from Dr. Crabtree’s data collection:

Schools Without Advertising Schools With Advertising
Have you smoked? 4% 3.5%
Daily Smoker? 1.3% 1.5%
Monthly Smoker? 2.1% 2%

Because there is no significant difference in the results, Dr. Crabtree concludes that the cigarette advertising has no effect on the teenage smoking rate.

Source of Bias: Areas being compared are only 5 miles apart, Student asked to raise hands in classroom.

Type of Bias: Sampling bias and measurement bias







PART 2: Designing your own experiment























Sources of possible bias in your experiment: