If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

## Statistics and probability

### Course: Statistics and probability>Unit 6

Lesson 4: Types of studies (experimental vs. observational)

# Observational studies and experiments

We do studies to gather information and draw conclusions. The type of conclusion we draw depends on the study method used:
• In an observational study, we measure or survey members of a sample without trying to affect them.
• In a controlled experiment, we assign people or things to groups and apply some treatment to one of the groups, while the other group does not receive the treatment.

## Problem 1: Drinking tea before bedtime

A study took random sample of adults and asked them about their bedtime habits. The data showed that people who drank a cup of tea before bedtime were more likely to go to sleep earlier than those who didn't drink tea.
question a
Which type of study method is this?

Another study took a group of adults and randomly divided them into two groups. One group was told to drink tea every night for a week, while the other group was told not to drink tea that week. Researchers then compared when each group fell asleep.
question b
Which type of study method is this?

## Problem 2: Social media and happiness

A study randomly assigned volunteers to one of two groups:
• One group was directed to use social media sites as they usually do.
• One group was blocked from social media sites.
The researchers looked at which group tended to be happier.
question a
Which type of study method is this?

Another study took a random sample of people and examined their social media habits. Each person was classified as either a light, moderate, or heavy social media user. The researchers looked at which groups tended to be happier.
question b
Which type of study method is this?

## Want to join the conversation?

• Are there any formal criteria to distinguish between a "sample study" and an "observational study"?

After reading the articles in this segment, it seems to me that there is a smooth transition.
E.g.: Problem 1: Drinking tea before bedtime from this page shows that researchers ask people and it is an observational study. During the exercises I had to mark such a case as sample study.
• Actually, the term is "Sample Survey" and you may search online for it. I think the difference lies in the aim of the three types of studies, sample surveys want to get data for a parameter while observational studies and experiments want to convert some data into information, i.e., correlation and causation respectively.
• What's the difference between observational and experimental studies?
(1 vote)
• a observational study is where nothing changes and just record what you see, but an experimental study is where you have a control group and a testable group.
• please illustrate the process of conducting experimental research by using an experimental and a control group simultaneously ,please give an example. thank you this will help me in accomplishing my assignment regarding research =)
• The process that goes along with conducting accurate research includes identifying the test subjects, materials, data collection, methods. Then follow the procedure of the experiment. Then test your hypothesis
• what is the difference between observational and experiment
• Observational is where you observe certain variables and try to determine if there is any correlation. Experimental is where you control certain variables and try to determine if there is any causality.
• Yeah so how do I submit this?
(1 vote)
• How do we submit this? It's not letting me.
(1 vote)
• oh I wonder that what the difference between the control and experiment group?
(1 vote)
• Ok, so a control group is a baseline. You know how the people are split up into groups? Let's pretend so lets pretend a researcher wanted to examine the effects of a certain type of people on somebody. The researcher, to perform an expirement, would split the people into 2 groups. One would be taking the pill and one would be taking a fake pill. The fake pill is the control group, it is a baseline to limit the effect of confounding variables. The experimnet group would be the one to take the actual pill. Also remember the people in each group are chosen randomly. Now lets take a look at problem number 2, the one that was blocked from social media use would be the control and the experimnet would be the group that people were being told to do something, the ne who were told to use social media.
(1 vote)
• The taste engineers at “Drinksoft” have developed a new formula for their major brand “Cola-Loca.” They wanted to know how tasty it is to teenagers compared to the old formula, so they decided to set up a blind taste test.
They randomly assigned 300300300 blindfolded, teenaged participants to two groups. One group was given the old formula of “Cola-Loca,” and the other was given the new formula. Each participant was asked to fill a formal taste 101010-point questionnaire, where 111 is considered "awful" and 101010 is considered "delicious."
What type of a statistical study did the engineers use?