The results are:

score

23 15th percentile

26 30th percentile

29 50th percentile (is this the mean?)

32 70th percentile

35 85th percentile

Maybe the mean and SD cannot be calculated with only this data?

Any help appreciated.

Thank you for your help.

- Thread starter saratogacoach
- Start date

The results are:

score

23 15th percentile

26 30th percentile

29 50th percentile (is this the mean?)

32 70th percentile

35 85th percentile

Maybe the mean and SD cannot be calculated with only this data?

Any help appreciated.

Thank you for your help.

They can. You already did the mean. Let's say you knew the standard deviation - how would you calculate what percentile a value falls at.

I looked up the 85th percentile in a Z table: 1.036. Not sure what formula to use to convert the 85th percentile value (35), or another score value, to a standard deviation?

Thank you for your helpful suggestion. While I think that I may be able to figure out the SD, I am beginning to wonder if the results are actually a normal distribution. I will first need to further check this out in the research study (I saw these results in a summary of the research) before concluding that it is a normal distribution. I think that if not a normal distribution, the graphing that I was hoping to do, using mean and SD and Excel, won't work.

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