Here's the question you clicked on:
lgbasallote
"All the names of a class were written on separate tickets. Ten tickets were selected after the names were jumbled inside a can...." This is an example of simple random sampling right?
Yes I believe so :D Since its random ;D
well...i know it's random....i just don't know the specific type of random sampling
Isnt there only one type? :O do u have choices lol? :P
it could be clustered random sampling....since they were grouped first... or maybe stratified random sampling since i don't know what it means....
no there isn't one type and no choices
I would probably argue that they're looking for clustered random sampling. They first divided some population up into "classes" and from this particular class, they made a simple random sampling. I see how this is confusing though. Since a clustered random sampling by definition has a simple random sampling in it...
Taking AP Stats, eh @Igbasallote? It's SRS.
clustered random sampling has something to do with grouping right @KingGeorge ?
@vf321 not taking it....it's complicated anyway why SRS?
One sec let me take my notes out with precise definitions.
clustered random sampling is when you split the population into multiple groups/clusters, and then take a simple random sample. By saying this was from a "class" it implied to me that they had divided the overall population into multiple "classes"/groups.
yes. my thoughts too
It's that fact that confuses the question a little for me. Since any example of clustered random sampling is an example of simple random sampling as well.
a lottery is a simple random sampling though...
Def 1. SRS is a sample selected from a population that ensures that EVERY possible sample of desired size has the same chance of being selected (i.e., random number generator - but, the College Board counts the shuffled names on tickets as random) Def 2. A population can be divided into non-overlapping subgroups called clusters which are internally heterogenous. Random selection of several clusters and then assessment of all internal individuals is cluster sampling.
...so how is it not cluster nor random?
You are taking ONE sample from your ticket pool, and each ticket has an equal chance of being drawn, assuming you take them at the same time, and do so randomly. You are NOT dividing the class into, say, desk groups and randomly choosing entire desk groups for your sample. QED, SRS.
**QED was necessary for style points.
Ah. It makes more sense now. In a cluster sampling, you also have to take a sample of each cluster. Hence, this can't be CRS, so it must be SRS.
^^I think that's the right idea. Feel free to shoot me down if it's wrong.
by SRS we're talking about simple? or stratified?
Simple of course. Stratified sampling can be thought of as homogenous clustering.
oh..i thought SRS meant stratified
And stratification would result in an internal SRS for each strata.
that was why i was confused with the definition
Well are you all clear now?
what is stratified random sampling then?
I told you, didn't I? "Stratified sampling can be thought of as homogenous clustering," but where each such homogenous cluster has an "internal SRS for each strata." I.e., you don't use the entire strata as your sample.
i meant....how does it look like...i not good with understanding stat words
you choose part of the cluster?
or you divide a population into different clusters and then you select one cluster?
Stratified sampling: I want to observe high school student's attitude towards school assemblies. I know that there may be varying attitudes over grade level. Strata: Freshmen, Sophomores, Juniors, Seniors. Take a SRS (simple RS) of each strata (make sure size of SRS is proportional to grade population): 30 rand selected fresh, 20 r.s. soph., 25 r.s. juniors, 20 r.s. seniors. Sample = 30 + 20 + 25+ 20
This is done so that I have a sample that represents my population well. A whole SRS of the entire high school of size 95 can end up with, say, 50 sophomores, which may skew the results.
but simple random sampling takes all of the population into account?
yes look at my definition above
like i said..im not good with stat words...just clarifying