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Main content
Current time:0:00Total duration:4:21
AP.STATS:
DAT‑2 (EU)
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DAT‑2.E (LO)
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DAT‑2.E.1 (EK)
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DAT‑2.E.3 (EK)
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DAT‑2.E.4 (EK)
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DAT‑2.E.6 (EK)
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VAR‑1 (EU)
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VAR‑1.E (LO)
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VAR‑1.E.1 (EK)
CCSS.Math:

Video transcript

a senator wanted to know about how people in her state felt about internet privacy issues she conducted a poll by calling one hundred people whose names were randomly sampled from the phonebook note that mobile phones and unlisted numbers are not in phone books the Senators office call those numbers until they got a response from all 100 people chosen the poll showed that 42% of respondents were very concerned about Internet privacy what is the most consorts concerning source of bias in this scenario and we should also think about well what kind of bias is that likely introduced is this likely to be an over estimate or in an underestimate of the number of respondents and maybe there is no bias here but our choices and the no bias is not one of the choices so you can imagine it's going to be one of these three so I encourage you to pause this video and think about what we just said we're a senator we're trying to figure out what percentage of respondents are very our of our constituents are very concerned about Internet privacy and we go to the phone book we sample a hundred people we keep calling them until they answer and we get that 42 percent are very concerned so so what's the source of bias all right now let's work through this together so non-response is would have been the case if we selected these hundred people and let's say only 50 people answer the phone and we didn't keep calling them then we'd say well you know 50 of the people who he sampled to answer our survey didn't even respond there was a non-response there what was there about those 50 people maybe there was something that would have skewed the survey or actually if we had we gotten them it would've gotten maybe get better data but in this case they tell us the Senators office called those numbers until they got a response from all 100 people chosen so the hundred people that they chose they made sure they got a response so non-response is not going to be an issue here all right next choice under coverage well under coverage is where you're not able to sample from part of the population and a part of the population that actually might because you didn't sample it it might introduce bias now let's think about what happened in this situation we are a senator we want to sample all of our constituents but we choose we instead we sample from the constituents who happen to be listed in the phone book so these are the people who happen to be who happened to be listed in the phone book and so we're not sampling from people who are not in the phonebook who are maybe have landlines and they're unlisted and we're not sampling from people who don't have landlines who only have mobile phones and you might say well why is that important well think about it people who decide not to list the in the phone book or people who don't even have a landline some of those people might be a little bit more concerned about privacy than everyone else they explicitly chose not to be listed so under coverage is definitely a very concerning source of bias over here we are sampling from only a subset of our entire population we care about in particular we're missing out on people who might care about privacy and so I would say because of under coverage 42% is likely to be an underestimate of the nut people concerned about Internet privacy they're probably a higher proportion of the people out here care about privacy because they're unlisted or they don't even have a landline so under coverage it probably introduced bias and it implies that 42% is an under under estimate of the percentage of the Senators constituents who care about Internet privacy now the last the last question volunteer response sampling well this would be the case where you you know the senator I don't know put a billboard out or or just told someone told a bunch of people maybe on her website hey vote for this or give us your information on how much you care about Internet privacy and that would have that would have been the source of bias there is well who shows up on that website you once again if you did hey come to my website and fill it out you're filling you're only getting you're only getting information from a subset of your population who is who are choosing who are volunteering that is not the situation that she did over here she she didn't ask a hundred people to volunteer her team went out and and got them from the phone book so this was definitely a case of under coverage
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