Observational Studies and Experiments chapter 11Basics of Observational studies

What is an Observational Study?

A study based on data collected by observations or records

There is no interference or manipulation of data – just observe what is happening.

Example: Collecting last quarter grades given by the teachers.

pg 1.2 – student example

Two Types of Observational Studies

Retrospective

Retro: selecting subjects and then collecting data about their past.

ProspectivePro: selecting subjects and then following them to collect data as they live their life.

pg 1.3 What does retro mean?pg 1.4 – what does prospective mean?

Experiments

Controlling all influences except the one thing (factor)

you want to test.You make a change in the factor and nothing else.

Prospective

pg 1.5 – difference between study and experiment

Nature and Scope of Conclusion

What did you find out and who/what does it apply to?

pg 1.6 – what does an experiment apply too?

B) Class ExampleResearchers who examined health records of thousands of men found that men who died of heart attacks tended to be shorter than men who did not.

1) Is this an experiment or observational study – if study, what kind?

2) Does this mean that shorter men are at a higher risk of heart attack?

pg 2.1 – answer

pg 2.2 – answer

C) Class ExampleCoffee stations in offices often just ask users to leave money in a tray to pay for their coffee, but many people cheat. Researchers at Newcastle University replaced the picture of flowers on the wall behind the coffee station with a picture of staring eyes. They found that the average contribution increased significantly above the well-established standard when people felt they were being watched, even though the eyes were patently not real. (NY Times 12/10/06)

Coffee stations in offices often just ask users to leave money in a tray to pay for their coffee, but many people cheat. Researchers at Newcastle University replaced the picture of flowers on the wall behind the coffee station with a picture of staring eyes. They found that the average contribution increased significantly above the well-established standard when people felt they were being watched, even though the eyes were patently not real. (NY Times 12/10/06)

C) Class Example

1) Was this a survey, observational study or experiment – if a study tell what kind.2) What are the variables they are interested in?3) What does “increased significantly” mean?

pg 3.1 – what is this?pg 3.2 – what is the variable of interest?pg 3.3 – what was changed?

Among a group of disabled women aged 65 and older who were tracked for several years, those who had a vitamin BI2 deficiency were twice as likely to suffer severe depression as those who did not.

D) Class Example

1) Was this a survey, observational study or experiment – if a study tell what kind.2) What are the variables they are interested in (parameter of interest)?3) Who were the subjects studied and how were they selected?4) What is the nature and scope of the conclusion?

pg 4.1 – what is this?pg 4.2 – what is the variable of interest (parameter)pg 4.3 – who are the subjects?pg 4.4 – scope of conclusion

Researchers have linked an increase in the incidence of breast cancer in Italy to dioxin released by an industrial accident in 1976. The study identified 981 women who lived near the site of the accident and were under age 40 at the time. Fifteen of the women had developed breast cancer at an unusually young average age of 45. Medical records showed that they had heightened concentrations of dioxin in their blood and that each tenfold increase in dioxin level was associated with a doubling of the risk of breast cancer.

e) Team Example

1) Was this a survey, observational study or experiment – if a study tell what kind.2) What are the variables they are interested in (parameter of interest)?3) Who were the subjects studied and how were they selected?4) What is the nature and scope of the conclusion?