This is pretty neat! My pH calues are going up and down smoothly!

My data has this interesting thing going on with pH!

Sometimes everything you're doing seems to be right, and you notice what seems to be a really neat trend to your data! As a contributor to the scientific body of knowledge it is important to look at your data and keep checking to see if you are being accurate. In this graph from a GLOBE school in Japan, we see what looks like a consistant and smooth trend of pH. It seems to follow the temperature to a remarkable degree, and even seems to be within a more or less acceptable range.

The data look good! Why the concern?

• It is quite unusual for natural processes to change pH by more than 1 or 1.5 units.
• Although temperature and pH are related to some degree, we would not expect such strong correlations as a result. The pH meters should also be designed to automatically correct for temperature. Was it in this case? Perhaps not...

What might be going on in this case?

• The trend is real! Its very important to keep track of your GLOBE data and to evaluate it regularly. If you decide that you are seeing a real trend, look for possible ways to explain it. Often seasonality or daily cycles in the natural world produce trends. Sometimes pH can reflect something going on upstream from a location! Imagine if your data was regularly at about 7 for a year, and then suddenly began to drop at the same time you heard that acid rain was getting worse! Your data could be reflecting a very real trend!
• On the other side of the coin, trends in data can very easily be related to measurement technique. Imagine that you were measuring a water source and found that your pH was steadily dropping, and had already dropped by 2 pH units. In this case, you might suspect that your calibration solution was inaccurate. If your pH meter was always being calibrated slightly differently that it should be, then your measurement for the real world might also be off.