AI-GEOSTATS: New list is open
Title: New list is open Good day everyone, Around 20% of the members have now moved to the new list and we should then to start to use it. Remember the new address of the list is ai-geostats@jrc.it The rules have not changed. I am sorry the move of the list was so chaotic but the previous mail server was on the edge of collapsing (90% of the email addresses were declared as unrecognized!). Since I could not find any support at the remote location, I decided to move the list to something that is more outdated in terms of technology but it will do what it has do and will be managed by people I can talk to face to face. I see this as an improvement for the long term management of the list. The majordomo server should be able now to redistribute your messages but one may still expect a few problems as these will appear only by using the list. Thanks very much again to all for your support and patience and long live ai-geostats@jrc.it Kind regards, Gregoire PS: Digby, please feel free to post your question again on skewed distributions __ Gregoire Dubois (Ph.D.) European Commission (EC) Joint Research Centre Directorate (DG JRC) WWW: http://www.ai-geostats.org The views expressed are purely those of the writer and may not in any circumstances be regarded as stating an official position of the European Commission.
AI-GEOSTATS: Skewed Distributions
Is it correct that the probability of being above or below the mean of a skewed distribution is not necessarily 0.5?
RE: AI-GEOSTATS: Skewed Distributions
Yes- Take a gold deposit with 99% of assays 0 gpt, 1% of assays 1 gpt. Mean is 0.01, prob 1 assay mean =99% Extreme case but true for lognormal as well. Robert (Bob) L. Sandefur PE Senior Geostatistician / Reserve Analyst CAM 200 Union Suite430 Lakewood, Co 80228 [EMAIL PROTECTED] 303 472-3240 (cell) -best choice 303 716-1617 ext 14 The content of this message may contain the private views and opinions of the sender and does not constitute a formal view and/or opinion of the company unless specifically stated. The contents of this email and any attachments may contain confidential and/or proprietary information, and is intended only for the person/entity to whom it was originally addressed. Any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this email in error please notify the sender immediately by return e-mail and delete this message and any attachments from your system. From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Digby Millikan Sent: Friday, May 19, 2006 07:44 To: AI Geostats mailing list Subject: AI-GEOSTATS: Skewed Distributions Is it correct that the probability of being above or below the mean of a skewed distribution is not necessarily 0.5?
RE: AI-GEOSTATS: Skewed Distributions
AI-GEOSTATS On 19-May-06 Digby Millikan wrote: Is it correct that the probability of being above or below the mean of a skewed distribution is not necessarily 0.5? Very much true that it may not be 0.5! As a general (though not absolutely true) rule, if a distribution is positively skewed then the mediam (0.5-point) is less than the mean, and for a negatively skewed distribution the median is greater than the mean. This often applies to the staddard distributions which turn up in practice. However, there is no general absolutely sure relationship between median and mean for non-symmetric distributions. Intuitively, the position of the median is independent of how you re-distribute the probability for values less than the median, and independent of how you re-distribute it for values greater than the median, so long as you keep 50% on either side. However, the mean is very much influenced by precisely where each bit of probability is located, so you can swing the mean around as much as you like without affecting the mediam. Best wishes, Ted. E-Mail: (Ted Harding) [EMAIL PROTECTED] Fax-to-email: +44 (0)870 094 0861 Date: 19-May-06 Time: 15:43:57 -- XFMail -- + To post a message to the list, send it to ai-geostats@jrc.it + To unsubscribe, send email to majordomo@ jrc.it with no subject and unsubscribe ai-geostats in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list + As a general service to list users, please remember to post a summary of any useful responses to your questions. + Support to the forum can be found at http://www.ai-geostats.org/
AI-GEOSTATS: Re: Skewed Distributions
DigbyIf your distribution has a positive skewness as calculated (bulks towards zero with long tail into high value) the proportion below the mean will be significantly higher than 50%. If negatively skewed -- e.g. Calcium in limestone, iron in iron ore -- more than 50% will be above the mean.The arithmetic mean is the equivalent of the centre of gravity -- one sample way out on the arm outweighs loads of samples close to the centre.Welcome all to the new list IsobelDigby Millikan [EMAIL PROTECTED] wrote: Is it correct that the probability of being above or below the mean of a skewed distribution is not necessarily 0.5?
