1.3 Gathering Data Objectives: By the end of this section, I will be able to… 1) Explain the main factors that go into designing a good questionnaire. 2) Understand the difference between an observational study and an experiment.

Five Factors for Good Questionaire Design 1. Remember: Simplicity and clarity. No four syllable words. 2. When reporting results, record the actual question asked. Don’t draw generalizations.

Five Factors for Good Questionaire Design 3. Avoid leading questions: “A child growing up poor faces more than his fair share of negligence and crime. Do you support the welfare system?” 4. Avoid asking two questions in one: “Have you tried drugs or alcohol?” 5. Words mean different things to different people: sometimes? often?

Questionaire Populations TARGET population: complete collection of all elements. TARGET population: complete collection of all elements. POTENTIAL population: collection of elements from the target population that had a chance of being sampled. POTENTIAL population: collection of elements from the target population that had a chance of being sampled.

Questionaire Populations SELECTION BIAS: when the population from which the actual sample is drawn is NOT representative of the target population. SELECTION BIAS: when the population from which the actual sample is drawn is NOT representative of the target population.

SURVEYING Suppose we want to find out how many Sallies students would support changing the current dress code at Salesianum. We go to the local mall on a Saturday at 10 am and survey high schoolers. We ask them, “Do you oppose or favor a new dress code for Salesianum students?” Suppose we want to find out how many Sallies students would support changing the current dress code at Salesianum. We go to the local mall on a Saturday at 10 am and survey high schoolers. We ask them, “Do you oppose or favor a new dress code for Salesianum students?” Identify our TARGET population. Identify our POTENTIAL population. Discuss any possible problems. Sallies Students HS’ers at the Mall

TYPES of Statistical Studies EXPERIMENTAL STUDY EXPERIMENTAL STUDY vs vs OBSERVATIONAL STUDY OBSERVATIONAL STUDY Researchers investigate how varying the predictor variable affects the response variable. When it is not possible to conduct an experimental study, researchers observe whether a subject’s differences in the predictor variable are associated with differences in responser variable.

Experimental vs. Observational We want to find out who will be voting for Obama in the next election. We are going to randomly interview 100 individuals in the area. Experimental or Observational?

Experimental vs. Observational We want to find out if high school students do worse on tests if they are hung over from partying the night before. We are going to randomly select 100 students for our study. Experimental or Observational?

Experiemental Studies Predictor variable: a characteristic in the study that will bring about an outcome Predictor variable: a characteristic in the study that will bring about an outcome Response variable: is an outcome brought about by differences in the predictor variable Response variable: is an outcome brought about by differences in the predictor variable

Sample Survey Create a sample questionaire for your fellow students. Create a sample questionaire for your fellow students. It can be directed at any group of individuals. It can be directed at any group of individuals. You must pick 1 topic. You must pick 1 topic. You must have 5 different questions about this topic. You must have 5 different questions about this topic.

Sample Survey Answer the following questions FULLY Answer the following questions FULLY 1. How you would randomly select your sample. 2. Who is your target population? 3. Who is your potential population? 4. Do you have a selection bias? EXPLAIN! 5. Is your study experimental or observational? EXPLAIN!