Previously, we examined censuses and surveys. We get the best data from a census because it includes the entire population. However, it's not always possible to conduct a census, so we often get our data from surveys instead.
When we take a survey it is important that the results are representative of the population. This means that the results that we get for any question we ask of the survey would be the same as if we asked it of a census. This also means that the mean, median, mode and range of the survey should be very close to the same results of the census (although getting exactly the same results is almost impossible).
If a survey is not representative, we call it biased. There are a number of potential sources of bias that we should avoid:
Consider the following questions and determine why they are inappropriate for a survey.
"How many large electronic devices are in your home?"
"Many people have worked incredibly hard and even died making this bridge. Do you like it?"
Consider the survey question and the sample and determine whether the outcomes are likely to be biased or not.
Rosey is asking people on her soccer team, "What's your favourite sport?"
James randomly selected people from his school to find about the school sports. He asked "What's your favourite school sport?"
Gwen randomly selected people from her school and asked, "The local AFL team is donating money to our school this term. What's your favourite sport?"
A survey asks the following two questions with the answers displayed.
What statement can be made from the results shown?
|Do you prefer reading, watching TV, or gaming?|
|Do you prefer studying, cleaning, or exercising?|
analyses single sets of data using measures of location, and range