Dear List, I think I'd like to state my problem more clearly. What I think to be the estimate of the overall variance is the expected variance in the future...
1797
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Meng, If your sample grid spacing is regular, I assume it wouldn't make much difference, however in mining drilling campaigns commonly have high amounts of...
1798
Colin Daly
Colin.Daly@...
Dec 9, 2004 5:56 pm
Meng-Ying
samples taken beyond the range are, in fact, far enough apart from one another! The sill is - to all intents and puposes - equal to the variance of...
1799
Rajive Ganguli
rajive.ganguli@...
Dec 9, 2004 5:56 pm
My question is general. What do you conclude if your variogram is wavy? Cyclic patterns? I have what appears to be high nugget, followed by a wavy pattern. ...
1800
Donald E. Myers
myers@...
Dec 9, 2004 5:56 pm
The sample variance (assuming that you use the "n-1" divisor) is an unbiased estimator of the population variance provided you use random sampling. Note the...
1801
George R Cutter
gcutter@...
Dec 9, 2004 5:56 pm
It was previously mentioned that a common approach is to subdivide populations into those of equal mean and variance so that stationarity is obeyed. What do...
1802
Isobel Clark
drisobelclark@...
Dec 9, 2004 5:56 pm
Rajive I haven't read the other responses yet, so this may be redundant. Two possibilities: (1) anisotropy: if this is shallow marine data there should be a...
1803
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Dear Meng-Ying, If you imagine the 1 million samples (total dataset and area) overlying a pattern of 1000 low and high grade regions, your 1000 sample set you...
1804
Isobel Clark
drisobelclark@...
Dec 9, 2004 5:56 pm
Digby I see where you are coming from on this, but in fact the sill is composed of those pairs of samples which are independent of one another - or, at least,...
1805
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
While your talking about sill's being the global variance which I read everywhere, isn't the global variance actually slightly less than the sill, as the ...
1806
Colin Daly
Colin.Daly@...
Dec 9, 2004 5:56 pm
Hi Meng-Ying The calculation of the experimental variance on a finite set of data (population or sample) is simply a mathematical operation - in itself it has...
1807
Meng-Ying Li
mengyl@...
Dec 9, 2004 5:56 pm
Isobel, I agree with you that no estimation is needed if we have the population, and that's what I said in the beginning of my last discussion. I'm saying that...
1808
Meng-Ying Li
mengyl@...
Dec 9, 2004 5:56 pm
Hi Isobel, Could you explain why it would be a better estimate of the variance when independance is considered? I'd rather think that we consider the ...
1809
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Meng-Ying, You seem to have a point the theory of using the sill is not a hard and fast rule, it is just if you're conducting a mine study and you plot a...
1810
Colin Daly
Colin.Daly@...
Dec 9, 2004 5:56 pm
Hi Meng-Ying
27 points - you can't really calculate a variogram. With a range of 3 - you have about 9 correlation lenghts in the field. So as a crude...
1811
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Meng-ying, I did mean the clustering of locations, if the sample is evenly and or randomly spread your s^2 estimate will be no problem, it's when the data is...
1812
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Meng-Ying, For interests sake could you perform the same experiment for a stationary sample set of size 1000. Regards Digby * By using the ai-geostats mailing...
1813
Isobel Clark
drisobelclark@...
Dec 9, 2004 5:56 pm
... Geostatistics applies to any size of sample set but for the theory to work ou have to have a relatively enormous population to draw rom. Put in plain...
1814
dwmccarn@...
Dec 9, 2004 5:56 pm
Dear Rajive: I cannot conclude with only 328 pairs that the feature is "wavy" because I do not know how those pairs are distributed for each point in the...
1815
Mat (University Accou...
m.pawley@...
Dec 9, 2004 5:56 pm
Hi Digby, Just a note - in circumstances that you have just described, the greater the level and range of autocorrelation means the more precise your estimate...
1816
Digby Millikan
digbym@...
Dec 9, 2004 5:56 pm
Mat, The point is the spatial randomness with which they were sampled. Typically in a mining situation core samples far from follow a spatially random sampling...
1817
Meng-Ying Li
mengyl@...
Dec 9, 2004 5:56 pm
Thanks Digby, You answered more to the question I asked. In this case I assume that you define the overall variance of a random field to be the variance of...
1818
Meng-Ying Li
mengyl@...
Dec 9, 2004 5:57 pm
Hi Colin, What I'm talking about in my example is comparing two descriptive statistics for this population which consists of 27 data points. No estimation here...
1819
Digby Millikan
digbym@...
Dec 9, 2004 5:57 pm
RE: [ai-geostats] Re: Sill versus least-squares classical variance estimateColin, You misunderstood me, the 1 million data is the total unknown dataset. Say ...
1820
Digby Millikan
digbym@...
Dec 9, 2004 5:57 pm
Meng, You wan't to have an evenly spaced sample pattern for you estimation of the variance, if you use samples within range of each others then these are...
1821
Colin Daly
Colin.Daly@...
Dec 9, 2004 5:57 pm
Hi Digby
Yes, I agree with what you say below - if your only aim was to estimate the variance and you only could collect 1000 samples - then choose them to...
1822
Isobel Clark
drisobelclark@...
Dec 9, 2004 5:57 pm
Meng-Ying Assuming that you generated your line with a Spherical model, range 3, 27 samples making 9 ranges the variance within that line will (theoretically)...
1823
Colin Daly
Colin.Daly@...
Dec 9, 2004 5:57 pm
Hi Digby
Sorry to say - but suggesting that less data is systematically better is mistaken - this is fundemental...and is contained in the intro pages of any...
1824
Isobel Clark
drisobelclark@...
Dec 9, 2004 5:57 pm
Meng-Ying We are talking about estimating the variance of a set of samples where spatial dependence exists. The classical statistical unbiassed estimator of...
1825
Digby Millikan
digbym@...
Dec 9, 2004 5:57 pm
Hole effect model, usually means your deposit has alternating high and low grade zones. Sorry I'm not familiar with the geology of this deposit but examples of...
