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I have data which is of similar type (though about a different subject) to that below and I would like to calculate averages per day so that I can compare between the different types of food. I would like to calculate the average weight of food eaten per day for different types of food.

I have calculated mean, standard deviation etc. of (food eaten/animal)/day as in the example shown below.

I also have the raw data, but I don't think I should just pool all the data together and take the average over all the days, as that would give more weight to results from certain days than others (whereas weather or other daily conditions changed from day to day and are likely to have had an effect).

I have seen on the internet and it makes sense to me logically as well, that it's probably not correct just to average the average, but I'm not sure how to go about comparing the different foods?

Food eaten

APPLES

10/12/2013: Mean = 1.8kg, s.d.= 0.5kg N=20

11/12/2013: Mean = 2.2kg, s.d. = 0.3kg N=6

12/12/2013: Mean = 3.1kg, s.d. = 0.4kg N=12

BANANAS

10/09/2013: Mean = 2.3kg, s.d.= 0.5kg N=10

11/09/2013: Mean = 2.2kg, s.d. = 0.3kg N=4

12/09/2013: Mean = 1.1kg, s.d. = 0.5kg N=10

CAKE

20/01/2014: Mean = 1.0kg, s.d.= 0.2kg N=8

21/01/2014: Mean = 2.0kg, s.d. = 0.3kg N=8

22/01/2014: Mean = 2.0kg, s.d. = 0.3kg N=4

etc.

I want to compare the amount of cake eaten with apples and bananas and several other foods.

I know there are a lot of other factors to consider here if I was really comparing food eaten. Actually my data is about something different I just don't want to put it on the website as it's owned by my company. Thanks!

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  • $\begingroup$ I kind of think averaging the averages would be more correct than pooling all the data together as it would give the same weight to each day. However then not sure how to calculate and describe in text the new 'n' or standard deviations etc. $\endgroup$ – shara Feb 7 '17 at 9:21
  • $\begingroup$ Ask the good question first! If you want the amount of apples eaten from , say day1 to day100, compared to the amount of eaten bananas, you can just compute the average amount of eaten apples, computed between day1 and day100, to the average amount of eaten bananas on this same period. Then, would this give you what you want. If no, you try and ask another more specific question. $\endgroup$ – Learn_and_Share Feb 7 '17 at 9:45
  • $\begingroup$ Hi, no, I want to know the average amount of each food eaten per day. For example, if someone is only given cake to eat, on average what weight of cake would a person eat over one day. Compared with... if only given apples what weight of apples would they eat over one day. I will reread my question, maybe I didn't write that very clearly. $\endgroup$ – shara Feb 7 '17 at 9:51
  • $\begingroup$ what does it mean when your write: Apples 10/12/2013: Mean = 1.8kg, s.d.= 0.5kg N=20? $\endgroup$ – Learn_and_Share Feb 7 '17 at 9:55
  • $\begingroup$ sorry I think the formatting is making it hard to understand, will try to fix: That means that on the 10/12/2013 over all the animals the mean weight of apples eaten was 1.8kg, with a standard devation of 0.5kg $\endgroup$ – shara Feb 7 '17 at 9:58
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From what I see, you have different variables: food type, different animals, several days.

Usually, you fix one or more variables and you try to understand something about the variability of other variables. Example, I could fix a animal kind (horse), fix food eaten (bananas) and ask the question. What is the average of bananas did the horses eat from day1 to day10? Then the answer would be to average over the number of days, taking only data related to bananas eaten by horses.

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  • $\begingroup$ ah, sorry, it's actually the same animal type, only one species, but yes different food types and different days $\endgroup$ – shara Feb 7 '17 at 10:07
  • $\begingroup$ @shara no problem, still same logic, again you have to know what you want to analyze, then selecting data that's relevant to answering your question. $\endgroup$ – Learn_and_Share Feb 7 '17 at 10:10

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