May 14, 2009 at 12:26 pm
We have online tests with multiple choice questions. Our instructors want to calculate standard deviation for each question. What is the best way to do this ? The selected answers are saved as:
Choice1 / Choice2.
There are some True/False type of questions also!.
thanks
May 14, 2009 at 12:59 pm
books online, look up STDEV
[font="Arial Narrow"]bc[/font]
May 14, 2009 at 1:12 pm
I checked the books online! it calculates on numeric fields only!.
How to apply to string expressions!
May 14, 2009 at 1:19 pm
as far as i know, there is no such thing....but I'm no mathematician;-)
[font="Arial Narrow"]bc[/font]
May 14, 2009 at 1:40 pm
me either!.
I have to make interesting calculations!:
1. STDEV per question.
2. Get top/bottom 25%: with a a catch:
did overall top 25% get this question right!
did overall bottom 25% get this question wrong!
Any suggestion to accomplish either #1 or #2 ?
May 14, 2009 at 1:45 pm
perhaps give each answer a point value.
if question 1 has choices A B C D, then value them as 1 2 3 4 and do your calculations on the values. i'm really not sure.
[font="Arial Narrow"]bc[/font]
May 14, 2009 at 10:19 pm
bc (5/14/2009)
perhaps give each answer a point value.if question 1 has choices A B C D, then value them as 1 2 3 4 and do your calculations on the values. i'm really not sure.
No this is an invalid application of Standard Deviation. Ordering of values is very significant to StdDev, if you make up an order arbitrarily then you will get arbitrary results
[font="Times New Roman"]-- RBarryYoung[/font], [font="Times New Roman"] (302)375-0451[/font] blog: MovingSQL.com, Twitter: @RBarryYoung[font="Arial Black"]
Proactive Performance Solutions, Inc. [/font][font="Verdana"] "Performance is our middle name."[/font]
May 15, 2009 at 9:01 am
like i said...."but I'm no mathematician;-)"
i think the teacher's question is either incorrectly phrased or the student's description (or interpretation) of the question is incorrect.
[font="Arial Narrow"]bc[/font]
May 15, 2009 at 9:41 am
bc (5/15/2009)
like i said...."but I'm no mathematician;-)"i think the teacher's question is either incorrectly phrased or the student's description (or interpretation) of the question is incorrect.
Agreed.
[font="Times New Roman"]-- RBarryYoung[/font], [font="Times New Roman"] (302)375-0451[/font] blog: MovingSQL.com, Twitter: @RBarryYoung[font="Arial Black"]
Proactive Performance Solutions, Inc. [/font][font="Verdana"] "Performance is our middle name."[/font]
May 15, 2009 at 9:51 am
chandrika5 (5/14/2009)
me either!.I have to make interesting calculations!:
1. STDEV per question.
Any suggestion to accomplish either #1 or #2 ?
Basically, we do not have enough information to answer this question in any valid way.
To do a StdDev, you need the same kind of information that you have to have for an Arithmetic Mean (AVG() function): A collection of numerical values.
The key here is they have to be numerical and "meaningfully" so. That is, the values must have real meaning as numerical values, not just as arbitrary numerals or IDs. The relative order of the numerical values is significant (i.e., that 3 > 2) as is their relative differences (i.e., that (4-2) > (4-3)).
Otherwise the StdDev is meaningless, as any AVG() would be also.
[font="Times New Roman"]-- RBarryYoung[/font], [font="Times New Roman"] (302)375-0451[/font] blog: MovingSQL.com, Twitter: @RBarryYoung[font="Arial Black"]
Proactive Performance Solutions, Inc. [/font][font="Verdana"] "Performance is our middle name."[/font]
May 15, 2009 at 10:27 am
We used to have a old e-learning system that does this. This is on a unix with a propriety DB. We moved to a new SQLSERVER 2005 based system. The new vendor does not have the STDEV reports that old system used to give. Our instructors just love this report. All the questions in the quiz are either multiple choice or True/False.
The STDEV report has:
1.STDEV per question and/or overall quiz.
2.Top 25% overall grade: performance % per each question
3. Bottom 20% overall grade: performance % per each question.
Based on the above information, the instructor determines if the question was really hard or misleading.
I can get #2 and #3: these are straight calculations: get the TOP/BOTTOM 25% and check their answers on each question: calculate the %.
Stuck with #1.
May 15, 2009 at 11:19 am
Can you show some schema and sample data?
[font="Arial Narrow"]bc[/font]
May 15, 2009 at 11:54 am
chandrika5 (5/15/2009)
The STDEV report has:1.STDEV per question and/or overall quiz.
2.Top 25% overall grade: performance % per each question
3. Bottom 20% overall grade: performance % per each question.
...
Stuck with #1.
You need to talk to someone who knows (or knew) what those StdDev numbers in the old report represented. StdDev has to be done on a collection of numerical values.
If it's easier, try to think of Averages instead (StdDev is really just a second order arithmetic mean type of average anyway). If you can figure out how to do an average, you should be able to do a StdDev also.
So the question "1.AVG per question and/or overall quiz", takes back to "Average of what per question?" Average number of correct answers? That we can do, though the StdDev on a simple ungrouped binary average is not that meaningful.
[font="Times New Roman"]-- RBarryYoung[/font], [font="Times New Roman"] (302)375-0451[/font] blog: MovingSQL.com, Twitter: @RBarryYoung[font="Arial Black"]
Proactive Performance Solutions, Inc. [/font][font="Verdana"] "Performance is our middle name."[/font]
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