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In an online survey about shopping habits, the following question was posted:

"Do you often shop online?"

A total of 120,456 individuals responded, among them, 70% said "yes". What is this type of survey called, where the people surveyed are only those who chose to participate? What is problematic with this sampling method?

Which of the four levels of measurement best describes the given data?

Work Experience: In a corporate research study, the number of years employees have worked at a company is recorded for a randomly selected group of workers.

Determine the type of data represented by the following: The exact weights of randomly selected newborn babies in a hospital, born in one month.

A study was conducted where the number of hours students spent studying was recorded and paired with their scores on a mathematics test. In this sample of paired data, what do r and �� (rho) represent?

The following are the response times (seconds) for customer support calls at a software company.

28 40 55 60 90 75 42 50 48 40 30 35

What level of measurement describes this data set?

A running track has the following lap distances in yards for $9$ different tracks: $400,350,375,425,300,390,410,365,$ and $380$. Convert these distances to feet, and determine both the mean and the median of the data in feet.

A researcher wants to study the effects of caffeine on concentration levels. To gather participants, the researcher invites $15$ colleagues from the office to join the experiment. Identify the sampling technique used, and discuss any potential sources of bias.