Average function

[Bernard Posner]

I am a teacher in the midst of creating a database containing information about the students in my classes (names, addresses, phone numbers, grades, etc.). One of my tables contains student test score information. I am having a problem using the AVERAGE function in a report, since it does not ignore blank fields. This is an issue, because on particular exams students are sometimes absent or excused. I normally record test scores in a field called "GRADES". However, when a student is "absent" or "excused" from an exam, I record that information in a separate field and leave the GRADES field blank. When Alpha Five calculates the average, it includes the records that contain these blank fields in the calculation. For example, if I gave two exams, and a student scored 100 on one of them and was absent for the other, Alpha Five would calculate an average of 50 (100 divided by 2 exams), even though the student took only one exam.

As I write this, it occurs to me that I might be able to solve the problem by creating a separate table that holds only absent/excused information, and link it to the table containing GRADES. Doing so would preclude my ever leaving the GRADES field blank. However, this appears to be a somewhat inefficient way to attack the problem. I would much prefer if there was a way to have Alpha Five ignore blank fields when calculating the average.

Thank you

[Ohlen Cartmell]

RE: Average function

You might try creating a field called taken as a logical field. Then create a calculated field that totals the tests taken. Say you called it tottaken adn defined it as:

if(taken,1,0)

this would total the number of tests taken.

Create another calculated field to total the test scores; say you called it totscores.

Then the average would be a third calculated field:

totscores/tottaken



Hope this helps.

[whanigsberg]

RE: Average function

Another way to deal with this problem is to store your marks in character fields. That way you can enter the remark (eg. exc)or the grade in the field. To calculate totals or averages you use the val function to conditionally convert the string to a number depending on whether the field holds a remark or a grade. Use lookups to restrict user input to valid remarks.

Bill

[bobsk]

RE: Average function

I got it! This will work pretty good. Use character fields for grades. That way you can leave it blank or put a big fat zero(if the student desrves one). I attatched a picture of a form I made. The one on the left has 4 records and the AVERAGE funtion uses all 4. That's not what you want. The one on the right is the good one. I "marked" the record that was left blank and applied a RANGE that showed only "unmarked" records. The COUNT function gave me the correct total needed to for the AVERAGE to be correct. You could place a script on the ONDEPART action to mark the record.

[urbanski]

RE: Average function

I use four fields -- field one indicates the number of points on the test 10 points, 15 points ect. field two indicates the score 9, 6, 5 ect. Field three is a calculated field called "counter". If the score field is empty the counter is 0, if it has a value, the counter is 1. Field four is a calculated field called grade (score divided by possible points times 100).
The average is the total of the grades divided by the total of the counter.

Regards
Jim