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rhlow
05-15-2012, 09:26 PM
Hello!

I have a question regarding calculating a standard deviation.

I have been taking plant measurements of a series of weeds. I had 4 plots in total, with 10 plants in the first plot, 3 in the second, 9 in the third and 13 in the fourth. Unfortunately I didn't take the plant biomass of each, rather, I took a total weight of each of the plants. As such, I have a total mass of 149.57 grams in the first plot, 12.91 grams in the second plot, 54.69 grams in the third plot and 23.47 grams in the third plot.

So when I calculate my standard deviation is my 'n' value 4, or is my 'n' value 35? I am wondering if I have limited my degrees of freedom by lumping the total biomass of all the pants in the plots.

Regards to all who respond to this! I appreciate it.

tkhunny
05-16-2012, 09:06 AM
What are you trying to do? Is it significant that there are four plots or are you just planting where you have space?

rhlow
05-17-2012, 01:23 AM
The experiment has already been conducted, and there were 4 reps in the trial. This is just one portion of what I am looking for, I just didn't want to bog people down with numbers. Does that help?

Subhotosh Khan
05-17-2012, 03:41 PM
Hello!

I have a question regarding calculating a standard deviation.

I have been taking plant measurements of a series of weeds. I had 4 plots in total, with 10 plants in the first plot, 3 in the second, 9 in the third and 13 in the fourth. Unfortunately I didn't take the plant biomass of each, rather, I took a total weight of each of the plants. As such, I have a total mass of 149.57 grams in the first plot, 12.91 grams in the second plot, 54.69 grams in the third plot and 23.47 grams in the third plot.

So when I calculate my standard deviation is my 'n' value 4, or is my 'n' value 35? I am wondering if I have limited my degrees of freedom by lumping the total biomass of all the pants in the plots.

Regards to all who respond to this! I appreciate it.

If all the conditions were same - you have 4 numbers and your n = 4.

There are procedures to deal with statistics of averages (in this case 14.957, 4.303, 6.115 and 1.806).

However, since the averages are so different - can you assume that those are from same population?