Right...I know this may sound pretty basic...but can anyone please tell me how to calculate the sample mean of participants' (children) exact age in years and months. One cannot use decimal points, like 0.7 does not equals7 months, right? What format then it is better to use? Using just months seems cumbersome, as some children are aged 15 years. Also when calculating standard deviation of the age how to account for missing values - some participants did not disclose their age.

Many thanks for your thoughts in advance. Rina

Sorry - reposting again with minor corrections
Changes: 04 Jul 2011 21:58:21
Right...I know this may sound pretty basic...but can anyone please tell me how to calculate the sample mean of participants' (children) exact age in years and months. One cannot use decimal points, like 0.7 - it does not equal 7 months, right? What format is it better to use? Using just months seems cumbersome, as some children are aged 15 years. Also when calculating standard deviation of the age how to account for missing values - some participants did not disclose their age.
Many thanks in advance, Rina

======= Date Modified 04 Jul 2011 22:29:36 =======
I'd either do it in months, or if you want years and months then convert to decimal places, i.e. 15 years and 6 months would be 15.5 etc.

As for the standard devation with missing values I'd work it out for the data you have, unless you can impute the values based on something else or there are al lot of missing values, and I'm not sure what to suggest then.

Hope that helps.

======= Date Modified 04 Jul 2011 22:35:36 =======
1. The months issue:

You are correct that it would be wrong to use 0.7 for 7 months. There are two possible ways of doing it:
(a) As you suggested, calculate everyone's age in just months, such someone who is exactly 15 would be 180 months. I would suggest that you convert back to years when reporting your findings.
or
(b) for the number of months beyond a certain year, divide the number of months by 12, then add the decimal on to the number of whole years. So for someone who is 8 years and 3 months old, calculate 3/12=0.25 and then add that to 8 i.e. that person is 8.25 years old. You can just do those month calcs once, and make a note of them so you can just add on the right decimal each time. But really you shouldn't be doing it manually - it would be easy to set up a batch calculation in Excel or another programme. Ask if you're not sure how to do this.

2. Missing data:
What percentage of your participants have no age data? If it's a couple you could consider excluding them from the analysis. If it's a lot then to do so could introduce errors such as bias in your findings. In such a case you might want to consider something called imputation - talk to a statistician about this. Here's a brief intro to some of the issues around missing data: http://en.wikipedia.org/wiki/Missing_data

Thank you so much Hazyjane and Catalynbond! After posting I just took a walk around the block because could not think straight about this thing, and when I came back I found your replies! (gift) How nice is that!!! Advice from you both make me want to keep going ;-) I have only one missing value of participant's age - I'll just exclude him. Right...I don't know how to set up excel calculation headache is gone:-)(up)(up) Nighty - night, Rina

======= Date Modified 05 Jul 2011 08:34:51 =======
Excel:

First column have the age in whole years. Second column have the months of age that are in addition to the years. Third column write a formula to divide column 2 by 12. Fourth column write a formula to add column one to column 3.

So for someone who was 8 years 6 months, then someone who was 3 years 3 months it would read:

8 / 6 / 0.5 / 8.5
3 / 3 / 0.25 / 3.25

If you have a lot of a data you don't want to be entering the years and months manually - it's too time consuming and you might make errors. So do get advice from someone in your dept about handling the data.