1.3 Gathering DataObjectives:By the end of this section, I will beable 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 PopulationsTARGET population: complete collection of all elements.

POTENTIAL population: collection of elements from the target population that had a chance of being sampled.

Questionaire PopulationsSELECTION 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?”

Identify our TARGET population.Identify our POTENTIAL population.Discuss any possible problems.

Sallies StudentsHS’ers at

the Mall

TYPES of Statistical Studies

EXPERIMENTAL STUDY

vs 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 StudiesPredictor 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

Sample Survey

Create a sample questionaire for your fellow students.

It can be directed at any group of individuals.

You must pick 1 topic. You must have 5 different

questions about this topic.

Sample Survey Answer the following questions

FULLY1. 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!