Statistics
Statistics
(OP)
Are statistics indeed invaluable as evidence in support of conclusions ?
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RE: Statistics
HVAC68
RE: Statistics
HVAC68.
For example, if a plant safety audit shows a yearly average of 10 dangerous occurrences (I refrain from using the word accidents to eliminate its connotation of chance), would a drop in that number to three be statistically significant ?
RE: Statistics
Regards,
RE: Statistics
If for example, the plant was running three shifts and had an annual average of 10 occurences, then backed down to one shift and the annual occurences dropped to three, then I would say no, it is not statistically significant. If on the other hand, the plant was running one shift with an annual average of 10 occurences, then doubled production with a drop to three in occurences, then that would be significant.
There is too much of the big picture missing to know what the measurement means.
Good Luck
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As a circle of light increases so does the circumference of darkness around it. - Albert Einstein
RE: Statistics
I was always tought that there are lies, damn lies, and stastics.
My answer would be that they are not valuable alone as evidence to support conclusions. They are only valuable in supporting the person that is authoring the conclusions.
Bob
RE: Statistics
If that is so - then as somebody pointed earlier, one has to look for consistency in these reduction - did it happen overnight ? or did it reduce linearly over a period of time ? If it's a reduction happening in a consistently linear manner (maybe even exponential !!!) - i.e. as long as there is a pattern that proves that the reduction is happening consistently, then, it proves that action has been taken towards achieving it.
HVAC68
RE: Statistics
Numbers waved around are worthless. Used responsibly, they are a valuable tool.
Hg
Eng-Tips guidelines: FAQ731-376
RE: Statistics
Numbers waved around are useless. The person using them responsibly is a valuable tool.
I am quite confident that I can make anything appear any way I want using statistics. It is how I use statistics that I will be judged by from my peers.
Bob
RE: Statistics
100% of people who eat bread die eventually.
RE: Statistics
Not necessarily. It depends on the overall statistics. What is the variance of the historical values? A sigma of 3 would put the new datapoint well within the statistical distribution of the historical data. Until you can collect sufficient data to show that there is a "new" average around 3, you really can't make any conclusions.
TTFN
RE: Statistics
There is a great quote attributed to former British Prime Minister Benjamin Disraeli - "There are three kinds of lies: lies, damn lies, and statistics."
RE: Statistics
Statistics, for all the uncertainty that comes with it, is a formal and rigorous discipline. No statistic is a lie; but there are plenty of liars about statistics. While some of you might argue that statistics is not engineering, engineering respect is based on the rigor of ones math. To cater to uneducated blather about statistics equated with damn lies from the mathematically challenged is to denigrate your own profession. Almost all aspects of engineering performance of materials, circuits, and systems are based on statistical behavior. I
f you think that statistics are lies and mean nothing, then you've basically laid claim that your own engineering analyses are so much horse manure; which they might very well be. For those who are PEs that believe that, they should immediately report themselves to their respective professional boards and declare themselves to be a danger to the public.
TTFN
RE: Statistics
Hg
Eng-Tips guidelines: FAQ731-376
RE: Statistics
One shouldn't blindly accept statistics without regard for the context. For example, take 25362's query: if a plant safety audit shows a yearly average of 10 dangerous occurrences, would a drop in that number to three be statistically significant?
What does the "drop" to three occurrences, from an average of 10, really mean? What is the standard deviation of the sample that produced the average of 10 occurrences? What if the average of 10 was produced from the following samples: 17, 5, 10, 1, 4, 30, 10, 4, 2 and 17?
Perhaps a better statistic is the frequency rate of occurrences (say per million man-hours), which is how safety statistics are usually reported.
RE: Statistics
HVAC68
RE: Statistics
scary (shiver)
25362, your question is a good one. You're basically asking if your stats mean anything. Look into the t test, Student-Newman-Kuels(sp) test, and Duncan's range test. Some others might exist too.
These have been helpful for me, and they could be useful in helping you decide if your data set is a) large enough to give you statisically relevent results, and b) to help you decide if the change in number of incidents you're observing is statistically "different."
RE: Statistics
Not quite MRM. That assumes that all practicing engineers actually graduated, and further assumes that all who graduated are still practicing.
Good Luck
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As a circle of light increases so does the circumference of darkness around it. - Albert Einstein
RE: Statistics
Statistics never lie. Like computers, they only do what you tell them to do.
Inputs can be garbage.
Constraints can be applied with a bias.
Results can be interpreted improperly.
The usefulness of statistics rely entirely on the competence and comprehension of the user.
...and a general rule for interpreting trends or forecasting: the more data points, the better.
RE: Statistics
Bob
RE: Statistics
Every drug you have ever taken, including any that may have save your life, was tested and then analyzed statistically.
Clinical testing and evaluation of drugs is probably one of the best gigs for PHD math types.
RE: Statistics
Maui
RE: Statistics
RE: Statistics
RE: Statistics
On the other hand, "significance", although not statistical in nature, can be attached to the total absence of occurrences.
For example, silo explosions of powdered Bisphenol-A during a March in Indiana, when motive air would be expected to be dry (with static electricity generation and no dissipation) when no such incidents happened in the humid environment of the Gulf Coast.
In this case "significance" refers to static charge generation as "probable" cause of dust explosions.
Would you like to comment ?
RE: Statistics
"would a drop in that number to three be statistically significant?"
That phrase "statistically significant," is well-defined and understood in statistics.
Because, presumably, you have only a single data point, it may or may not be statistically significant, because, even if it is grossly out of the norm, it may well be a fluke; as alluded to by others, your plant's "Typhoid Mary" or "Martin" may have missed days for other reasons.
Even in your latest posting, significance can still be asked from a statistical perspective. You posit some number of explosions in a specific month, March, but presented no data for either location. Without the data, you cannot statistically demonstrate significance.
Likewise in your original posting and subsequent ones, you still have not presented any background to your numbers, hence, there can be no conclusion drawn from a statistical perspective.
TTFN