
Help Explaining RMS to LAYMEN
“There are three kinds of lies: lies, damn lies, and statistics.” ???
I have 2 guys who use GPS (Carlson BRX7 with SurvPC and Trimble R8 with Access). They are laymen or “button pushers” if you will. I want them to understand the *** PRACTICAL USE *** of the numbers they see when looking at their GPS shots. Multiple sessions, amount of time per session, separation of sessions, repeatability, adjustment, removal of blunders, etc. is another discussion.
The two numbers I want them to understand (*** FOR PRACTICAL USE ***) is RMS (hrms, vrms) and standard deviation. These are what they see on their data collectors.
Standard deviation is easy: (1) show/explain a normal distribution – no numbers, no statistics, just a graphical bar plot; (2) show average/mean/middle of normal distribution plot; (3) show +/ 34.1% of the collected solutions from the average/mean/middle. Discussion of the significance when 68.2% of your 120 (or whatever) observations are within 0.01′, 0.02’…0.1′, 0.2′, etc. They got it – one guy asked what 2 standard deviations meant (95%)…the other guy is not as smart & didn’t care (mom dropped him on his head, and we claim he is adopted).
Where I fail is explaining RMS. I can’t seem to do so without wanting to get into some math, AND THIS IS WHERE I FAIL. I need a layman’s explanation and application. I want a better explanation than “smaller is better” or “don’t go above this number”. Maybe this is all my explanation should be? Maybe I should just say forget RMS and key on standard deviation? I want a 510 minute conversation – maybe a single page printout of some sort.
Thoughts or ideas? What would you do? Remember, this needs to be for layman.
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