Covariance between Index A and B calculator, between, numbers, please, points

wildrose

A:
-6.4
6.6
12.9
3.2

B:
-6.2
19
-7.7
4


It asks for the covariance...I plugged the numbers into their respective data points in my calculator and got 10.37...wrong answer. Correct answer was 13.82

The explanation says, when done out by hand, you would use n-1 in the denominator when dividing the summation of all the covariances...i thought this was only done for samples?

Help please, thanks.

siavosh

why do we do this step:


.13945 = x/(99.032) ??

ramdabom

got it guys. thanks for everything. GOOD LUCK TOMORROW

Daniel1985

^^ billy the other numbers are for linear relationships, regression and intercept. this function assumes x (independent) and y (dependent) variables. it is immaterial for what we will be tested on.

koba

Sorry....for Q 115:

look at the probability part of the question. since they arent all equal, you need to "trick the calculator" becuase the calc thinks every X and Y you enter into the sheet have an equal probability.

To trick the calc, a 20% probability is just two 10% probabilities, so enter the x value 2 times. We'll use 10 total inputs, so 2/10 is 20%.

Same for a 40% probability....just enter the value 4 times.

apply this to the full set and you end up with 10 total x values with probabilities equal to the number of times you used the value...



Edited 2 time(s). Last edit at Friday, June 5, 2009 at 02:17PM by june2009.

Kiakaha

That's so awesome. Thanks so much for that guys. Helps a ton.

What do the other variables mean? (a, b, Sigma(X), Sigma(X^2), etc.)

No easy way to get around hypothesis testing with similar methods, is there?

sgupta0827

This question was 117# in the mock morning exam. It doesn't have any texts. Does anyone know what would indicate that it should be computed as a sample?

kmf229

you so lost me...
but definitely thanks for the other one cause my head was spinning going back and forth from paper to calculator trying to get it.

bapswarrior

well thanks to both you and cpk then.

any fast ways to do #115 in the mock exam morning session?

dcfox83

On the ti

2nd Data (7 key)
enter x and y varianbles
Quit

2nd Stat (8 key) use arrows to find r (correlation) and Sx is sample stnd dev of x, the (standard deviation greek letter) is the population stnd dev.

Saves a lot of time. easy to learn.