VRAndy
Well-Known Member
- Joined
- Sep 23, 2008
- Messages
- 1,127
In this case the population we're interested in is the 3500 or so Pandora orderers. And the population we've "measured" is the 250 or so people who read the poll and decided to reply to the poll. (Who may or not have already pre-ordered!).
What a Silly example. In that situation you WANT only the self-selected students. Who cares what grades non-students would have gotten had they been students? There is no selection bias in the example you just cited. The population you are interested in is the student population, and you can have accurate measurements on 100% of that population.
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IIRC the Nielson ratings used to be extremely self-selected as well, since the results came from boxes that the end user had to not only know about and agree to, but manually control to indicate what they were watching at any time of the day!
Nielson uses a variety of methods. Including polls and set-top boxes like you say. (The boxes are automatic nowadays.)
But Nielson intentionally choose their sample carefully so that the demographics of their sample size match the demographics of the nation at large. You can't just call up Nielson and decide to participate in a poll, or a set-top box program. They call you if they need someone like you, And if you refuse, they try to find someone like you.
Nielson works very hard to avoid any sort of selection bias.
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You can't draw much in the way of conclusions from the others except that, perhaps, they don't like the forum much
If they're interested in poll data, and I'm not saying that they should or shouldn't be, but if they are, they should not rely on a self-selected one in a forum that only certain customers use. If they want a poll they should conduct it themselves. It's entirely possible to send an email poll to the entire list of existing customers.
The forums here are (Probably) heavily biased in favor of one or both of the following groups :
1) The people who are anxious over their $300 "investment" and want to either complain, or be reassured that they haven't wasted their money.
2) The people who are complete enthusiasts in the project and want to be involved at every step of the way. This people will hold out to the bitter end.
Either of those biases will skew the poll in one direction or the other, but it's impossible to tell which or by how much.
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