Population vs. Sample Clarification

[mjdav]

I had this question on a Quiz in my Intro to Stats class:



As you can see, my gut reaction was all the women in this country were the population, and that the 12,075 women surveyed were the sample. It turns out C and D were the correct responses, and I am having a really hard time understanding why.

Aren't the immunization statuses the parameter/statistics? It seems like C and D lump the parameter in with the population, and the statistics in with the sample. What am I missing here? There were 16 questions of this sort and this is the only one I missed, so I really want to address the gap in my reasoning. This was the explanation given, but I don't quite understand it and haven't seen it explained that way in the text:



In another problem we were told the emissions of a new car model were being measured and asked what the population was, and the correct answer was all of the cars of that new model. So why in that case was it not lumping in emissions with the cars for the population?


Apologies if my question is unclear, I'm having a hard time articulating it.

 

[lex]

I see your problem. I've never come across this distinction - but statistics is not 'my thing'.
The only difference I can see in the two situations is that in the first one there is only one characteristic (immunisation status) and so they can think of immunisation status as the thing being sampled, but in the second, they are looking at two different characteristics of a car - emissions and performance, so they might consider the car as the thing being sampled?

 

[mjdav]

Thanks for the reply lex.

I don't know, there was another question on this that was a woman wanting to know the percentage of her potato plants in her garden that had potato bugs on them, and the correct answers were population was all the potato plants in her garden, and sample was those that she examined. In that case it seems the same - potato bugs or not, vaccinated or not - and my brain is just unable to see the distinction.

 

[lex]

Yes, the 'potato bug status'. Of course they may not know the distinction themselves! It's sometimes a mistake to assume that. Sorry I couldn't be of help. Let us know if you ever discover an answer.

 

[mjdav]

It looks like you were right, lex! I received this excellent explanation on Wyzant, and NOW it makes sense when, as you said, you treat the records themselves as what was being sample. Case closed thanks to one David B. And actually his point about the populations being identical either way kind of blew my mind:

"You are right. It is confusing and a poorly written question. What is NOT being said in the question is that according to the answer, the survey was NOT made of the women but of their immunization records.

We know this NOT from anything in the question or the proposed responses, but in the answer they gave AFTER a selection was made. In other words we can deduce by inference that the immunization status's were sampled, not the women themselves. (say from doctors records). We can only make this decuction AFTER we know the right answer so the question is faulty.

If the women were themselves questioned about their immunization status than that would be the population.

I suggest you confront the instructor and ask from what information in the question can one make the assumption that only the records were surveyed, not the women. Especially as the question was very specific "In a survey of 12,075 WOMEN" . no mention of the survey being made of the women's records.

as a side note, nothing is included to state that anything other than 100% of women have immunization records [i.e. nothing to refute that is mentioned]. In that case the population of women's records and the population of women, in this context, are identical populations. Tsk Tsk.... such poor wording.,

That being said, this happens even more in real life. A boss asks for one thing, thinks they are asking for something else, and interpret the results as a third thing and then thinks they are all the same when they are not. Happens all the time."

 

[lex]

Thanks for posting the reply. Yes, I had noticed that the phrase 'survey of 12,075 women' in the question certainly suggests that the women were the population; a question which was impossible to answer. I think your answer was the most sensible in the circumstances.