Re: AI-GEOSTATS: values normalisation with a lot of zero!
I don't understand your point here about the additive constant. I took into account the additive constant 1 because of the unfeasibility of log(0). However, this transformation is useless, because it maintains the zero values! How could I transform my data to make a normalisation? Duccio -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and unsubscribe ai-geostats followed by end on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
Re: AI-GEOSTATS: values normalisation with a lot of zero!
you might try a tobit assumption. brian Brian Gray USGS Upper Midwest Environmental Sciences Center 2630 Fanta Reed Road, La Crosse, WI 54602 608-783-7550 ext 19 - Onalaska campus or 608-781-6234 - La Crosse campus fax 608-783-8058 [EMAIL PROTECTED] * |-+ | | [EMAIL PROTECTED]| | | Sent by: | | | ai-geostats-list@| | | unil.ch | | || | || | | 08/20/2003 06:35 | | | AM | | | Please respond to| | | rocchini | | || |-+ --| | | | To: [EMAIL PROTECTED] | | cc: | | Subject: AI-GEOSTATS: values normalisation with a lot of zero! | --| I would make a regression between water depth (field values) and the near-infrared band of quickbird satellite. The distribution of water depth values is not gaussian because of several values equal to zero. I can't make a transformation by log(x+1) because the result should be the same!! What could I do?! Thanks Duccio Rocchini [EMAIL PROTECTED] -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and unsubscribe ai-geostats followed by end on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and unsubscribe ai-geostats followed by end on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
Re: AI-GEOSTATS: values normalisation with a lot of zero!
I can't make a transformation by log(x+1) because the result should be the same!! I don't understand your point here about the additive constant. You also have to be careful with regressions on log transforms because the 'back transform' is not simply take the anti-log and subtract the added constant. Isobel Clark http://ecosse.ontheweb.com/whatsnew.htm Want to chat instantly with your online friends? Get the FREE Yahoo! Messenger http://uk.messenger.yahoo.com/ -- * To post a message to the list, send it to [EMAIL PROTECTED] * As a general service to the users, please remember to post a summary of any useful responses to your questions. * To unsubscribe, send an email to [EMAIL PROTECTED] with no subject and unsubscribe ai-geostats followed by end on the next line in the message body. DO NOT SEND Subscribe/Unsubscribe requests to the list * Support to the list is provided at http://www.ai-geostats.org
