Lies, damned lies, and....

[bathsheba666]

Statistics

Our au-pair just asked for help with a psychology paper, as she hasn't done statistics.
I haven't done stats for about 35 years, and am stuck.

She has 15 numbers, and has calculated the:
mean
variance (average of squares of individual differences from the mean)
standard deviation ( square root of variance)

However, the exercise pretty explicitly wants her to also calculate the:

..standard deviation for each individual number...

I have no idea what this is.
Can anyone help?

 

[ArneHD]

http://en.wikipedia.org/wiki/Standard_deviation#Definition_and_calculation

Here you go.

 

[Yoda Power]

Doesn't she have some textbook which explains it?

 

[Samson]

Statistics

Our au-pair just asked for help with a psychology paper, as she hasn't done statistics.
I haven't done stats for about 35 years, and am stuck.

She has 15 numbers, and has calculated the:
mean
variance (average of squares of individual differences from the mean)
standard deviation ( square root of variance)

However, the exercise pretty explicitly wants her to also calculate the:

..standard deviation for each individual number...

I have no idea what this is.
Can anyone help?

I am fairly sure that ther is no such thing as the standard deviation of of a single number. I would guess that the is a mistake on the paper or someone has read it wrong. I would guess they are asking her to calculate the standard deviation of sub-groups of this 15 (are the 3 grougs of 5?) or perhaps esstimate the population standard deviation (IIRC that involves you dividing by the sample size -1 where you would divide by the sample size to calculate the sample standard diviation, but check),

if you need more help you could post the exact question here.

 

[bathsheba666]

Thanks for all your responses.

http://en.wikipedia.org/wiki/Standard_deviation#Definition_and_calculation
Here you go.

Thanks, but...

...that was the first thing I turned to, and I still cannot see/understand what might be relevant to my point.

Doesn't she have some textbook which explains it?

Good question. No. The course (masters psychology) assumes knowledge of stats.

I am fairly sure that ther is no such thing as the standard deviation of of a single number.

That's what I thought. Hence the question.

I would guess that the is a mistake on the paper or someone has read it wrong.

I would guess they are asking her to calculate the standard deviation of sub-groups of this 15 (are the 3 grougs of 5?) or perhaps esstimate the population standard deviation (IIRC that involves you dividing by the sample size -1 where you would divide by the sample size to calculate the sample standard diviation, but check),

if you need more help you could post the exact question here.

Here is the question:

Background is 15 items, (scores between 1 and 5).

1) Total your scores across the 15 items.
Score=?

2) Calculate a mean and standard deviation for the class.

3) How would you interpret the overall agreement/disagreement with Freud's position?

4) Next, calculate means and standard deviations for each of the 15 items separately.

5) What items seem to elicit the most agreement? Disagreement? Why?

So, questions 1 & 2 we have, 3 & 5 I don't care about,

and 4 is the killer....


====

In case anyone cares:

Joan Cannon:
Personality Psychology: Insight, Issues, Case Histories, amd Applications.
pp283-284: Scoring.

 

[Samson]

Here is the question:

Background is 15 items, (scores between 1 and 5).
...
4) Next, calculate means and standard deviations for each of the 15 items separately.

So there is a list of 15 numbers from 1 to 5, something like Background = 1,2,3,4,5,4,3,2,1,2,3,4,5,4,3? I am fairly sure this makes no sence at all, means and standard deviations can only apply to groups of numbers not single numbers. Could it be a trick question?

 

[Truronian]

Is it defiintely not a number of people entering scores in the fifteen items?

 

[Ayatollah So]

It's got to be what Truronian said. For example, you might have the SAT test with 15 geometry questions, and lots of test-takers answering each question. You can calculate the mean and stdev for geometry questions as a "class", or you can calculate means and stdevs for each "item" (question).

 

[JerichoHill]

Yeah, there is no standard deviation of a single observation

 

[holy king]

Yeah, there is no standard deviation of a single observation

this is so poetic....

 

[bathsheba666]

Cool, thanks guys, that stiffened my backbone.

 

[GinandTonic]

Our au-pair just asked for help with a psychology paper, as she hasn't done statistics[...]

So hard to get good staff these days

 

[bathsheba666]

So hard to get good staff these days

But she is.....