Lid or no lid-- scientifically explored

At work, I like having a warm cup of tea because my office is cold. Well, also because I really like tea. Well, my tea is typically cold before I even get half way through with my tea. I blame it on a cold office (though I can imagine a dear friend of mine arguing that it is because I am just a slow tea drinker).
I had been trying to find ways of keeping my tea warm, given the materials I had available. Today, I decided I was going to do this scientifically-- meaning, isolating variables and testing it out! I wanted to compare whether a tall cup with a smaller opening and no lid was the same, better, or worse at keeping my tea warm than a shorter wider but lidded cup.

I used approximately the same amount of green tea (+/- 5 milliliters) at approximately the same temperature (+/- one degree celsius) in each.

I started off with both cups open to the air (unlidded). The initial temperature was 70 degrees C. After about two hours, the wider cup dropped to 27 C and the skinnier cup to 29 C-- after error analysis, it is apparent that there is not statistical significance to the temperature difference.

In the second phase of the experiment, I started off the two cups at about 79 C and placed the lid on the wider cup. The lid was made of the same ceramic material as the rest of that cup. Though both cups were made of ceramic, it is unclear of they are the same kind of ceramic material, molecularly speaking. But for now, I am going to assume that they were similar enough because they felt like they were the same. Well, after approximately two hours, the lidded cup dropped to 32 C and the unlidded skinny cup dropped to 31 C. Clearly no statistical significance.

So, according to this preliminary study, it seems that lids don't do much.

Okay, so I have to admit, these were not tightly controlled experiments but for the purposes of the experiment (and also for this blog) they were good enough. As it turns out, a possibility why the two resulted in such similar patterns may be because the openings of both cups were really not that far off from each other (one was 3 1/8 inch and the other was 3 3/8 inch). Future work can be directed toward exploring the question: At what point will the width begin to make a difference? The rationale for this question is that surface area, in particular the top surface area, makes a lot of difference in how quicking something cools. Here, it seems that a difference of 1/4 inch doesn't seem to matter much.