Desperate....Anyone know statistics.

[srbbnd]

Got a test tommorow and I'm screwed. If anyone could show me how to do this problem I will give you a cookie.

1.An economist is studying income in Duval County and wishes to make a guess at population mean income. She takes a sample of size 7, with following results (in thousands of dollars): 30,50, 80, 25, 100, 75, 90. Construct the 95% confidence interval for true population mean income in Duval County.

[Dhar_2]

Re: Desperate....Anyone know statistics.

dude. if u dont know it now. your pretty much up shit creek without a paddle.

good luck!

[beanzncheez]

Re: Desperate....Anyone know statistics.

4.

[AndyH]

Re: Desperate....Anyone know statistics.

$6.79ph

[threehills]

Re: Desperate....Anyone know statistics.

Using degrees of freedom, six in your case you should be able to plug it into the equation below.

Confidence Interval for a Small Sample

When the population is normal the sampling distribution will also be normal, but the use of s to replace s is not that accurate. The smaller the sample size the worse the approximation will be. Hence we can expect that some adjustment will be made based on the sample size. The adjustment we make is that we do not use the normal curve for this approximation. Instead, we use the Student t distribution that is based on the sample size. We proceed as before, but we change the table that we use. This distribution looks like the normal distribution, but as the sample size decreases it spreads out. For large n it nearly matches the normal curve. We say that the distribution has n - 1 degrees of freedom.

Example
Suppose that we conduct a survey of 19 millionaires to find out what percent of their income the average millionaire donates to charity. We discover that the mean percent is 15 with a standard deviation of 5 percent. Find a 95% confidence interval for the mean percent.

Solution
We use the formula:

(Notice the t instead of the z)
We get
15 tc 5 /
Since n = 19, there are 18 degrees of freedom. Using the table in the back of the book, we have that
tc = 2.10
Hence the margin of error is
2.10 (5) / = 2.4
We can conclude with 95% confidence that the millionaires donate between
12.6% and 17.4% of their income to charity.

[lilsensa]

Re: Desperate....Anyone know statistics.

I fucking hated statistics!!!! Worst class I have ever taken in college. The teacher was Indian, and no one could understand him..Fuck stats.

[Miroslav]

Re: Desperate....Anyone know statistics.

dude that shit's not not hard. threehills has the academic version up there for the student's t distribution. That distribution is preferable for smaller sample sizes, but I'm assuming your teacher is probably getting at using the normal distribution just for illustrative purposes - at any rate, I'm too lazy to look shit up in a table! Note: everything is rounded to 1 decimal place. I also haven't messed with this in a bit, so I take no responsibility if I'm full of shit. If anyone sees anything wrong with this, please speak up and I'll correct it.

First, the formula I'm working towards is this one (CI assuming a standard normal distribution with 95% confidence): CI = mean +/- 1.96 x std. error

now, step by step:

1. Get the mean. (30 + 50 + 80 + 25 + 100 + 85 + 90)/7 = 64.3

2. Get the variance. I'll do it in two steps to make it look simpler.

(30 - 64.3)^2 + (50 - 64.3)^2 + (80 - 64.3)^2 + (25 - 64.3)^2 + (100 - 64.3)^2 + (85 - 64.3)^2 + (90 - 64.3)^2 = 5,221.4

5,221.4 / (n - 1) = 5,221.4 / (7 - 1) = 870.2

3. Get the standard deviation. sqrt(870.2) = 29.5 sqrt means take the square root.

4. Get the standard error of the mean. std. error = std. deviation / sqrt(n)

29.5 / sqrt(7) = 11.1

5. Determine the standard deviations relative to the mean of a standard normal distribution (normal distribution standardized so mean = 0 and a std. deviation = 1). This depends on the precision of the confidence interval you're trying to compute. The common rule of thumb is that 95% of the area of the normal distribution is within 1.96 standard deviations of the mean. There is a lot more to say on this and you could do this based on t distributions and other stuff - if you're going to use the t distribution, you'll need to be provided with a table that gives you the right t score for your degrees of freedom (6) and desired confidence level (95%). But I'm going to leave that be.

6. Compute the confidence interval. = mean +/- 1.96 x standard error

lower bound: 64.3 - 1.96 x 11.1 = 42.5
upper bound: 64.3 + 1.96 x 11.1 = 86.1

ANSWER: 95% confidence interval: 42.5 to 86.1.

It's fricken huge because you have such a small sample size.

good luck! you'd better start doing some practice problems asap...

[Life on Other Planets AKA Johns]

Re: Desperate....Anyone know statistics.

Got a test tommorow and I'm screwed. If anyone could show me how to do this problem I will give you a cookie.

1.An economist is studying income in Duval County and wishes to make a guess at population mean income. She takes a sample of size 7, with following results (in thousands of dollars): 30,50, 80, 25, 100, 75, 90. Construct the 95% confidence interval for true population mean income in Duval County.

[beanzncheez]

Re: Desperate....Anyone know statistics.

The teacher was Indian, and no one could understand him...

Racist.

[Life on Other Planets AKA Johns]

Re: Desperate....Anyone know statistics.

Hi Beanz..Not sure if u saw my where is Beanz thread. Welcome back

[Huggie Smiles]

Re: Desperate....Anyone know statistics.

It's fricken huge because you have such a small sample size.

..

aint that the truth!

[beanzncheez]

Re: Desperate....Anyone know statistics.

Hi johns. I saw it. I heard about it. I laughed at the ignorance on that thread. And people wonder why there is such a huge lack of understanding and so many problems in this world. People are too used to having their father's cocks in their asses.

Now back to this thread at hand... did he fail?

[88Mariner]

Re: Desperate....Anyone know statistics.

Can anyone answer this question?

1. Sasha is tabbing records in his record box and wishes to make a guess at the record mean minimalness. He takes a sample size of 10, with the follwoing results (in bpm terms). 15,12, 11 16, 21, 24, 32. Construct the 95% confidence interval for true record mean minimalness in his record box.













(ok, it's a trick question. sasha doesn't use records anymore.)

[lilsensa]

Re: Desperate....Anyone know statistics.

Who wants to sample size my ball sack?

[threehills]

Re: Desperate....Anyone know statistics.

^ Oh baby, give me the square root of that!