What is the main analogy discussed in the passage?

• Ideas spread like diseases

• Diseases spread like ideas

• Ideas spread like wildfire

• Diseases spread like rumors

According to the passage, what is a major challenge in studying the spread of ideas?

• Ideas are nebulous and insubstantial

• Ideas spread too quickly

• There are too many ideas to study

• Ideas are too complex

What was the focus of the study mentioned in the passage?

• How social contagion works through Facebook

• The spread of diseases through populations

• The psychological impact of social media

• The effectiveness of marketing strategies

What did the researchers find to be the best predictor of someone joining Facebook?

• The number of distinct groups an individual could link up with

• The number of friends already on Facebook

• The frequency of Facebook usage

• The popularity of Facebook in their area

What does the passage suggest about using epidemiology models for studying ideas?

• It might not be wise to apply them naively

• They are perfectly suited for studying ideas

• They are more effective than psychological models

• They are outdated and need revision

What does the passage imply about the relationship between social networks and joining Facebook?

• More distinct social groups increase the likelihood of joining

• Having more friends on Facebook decreases the likelihood

• Social networks have no impact on joining

• Only family connections matter

What is the passage's stance on the need for social psychologists?

• They should develop their own models

• They should continue using epidemiology models

• They should focus on diseases instead

• They should collaborate more with marketers