About 75 years ago, Astronomers used the simple technique of correlation to discover the Universe was expanding. For nearby galaxies they measured a redshift and plotted that against the distance to the galaxy. Here is the data:
The line through the data is a "best fit" linear relationship which shows that there is a linear relationship between the the velocity at which a galaxy moves away from us and its distance. This linear relatinship is consistent with a model of uniform expansion for the Universe.
Returning to Salmon:
For the Bonneville Dam data:
What about Steelhead vs Chinook at Bonneville Dam:
Formally there is a very little correlation. The correlation coefficient, r, is 0.31. But look at the data closer to notice that its kind of odd.
There are 9 distinct occurences where the Steelhead Count is significantly above average (this corresponds to counts above 250,000). If we ignore those 9 points (years) out of the total of 57 years worth of data, the average Steelhead count is
The mean count for those 9 higher years is
Is the difference in these means significant?
One can therefore to conclude that something produces very high Steelhead Counts. Examining the data in time shows that the high Steelhead Counts occured in 1952--1953 and again in 1984-1989 and 1991-1992. High Steelhead count, however, does not mean high chinook count (nor does it correlate with anyother species)
For the whole data set, the weak correlation (r = 0.31) is shown below:
While a social scientist might argue that a correlation exists, you should be able to do better than that.
Okay, what about using just the chinook counts as a tracer of the entire salmon population. How well does that work? Here is the data:
Your eye sees a correlation and indeed r = 0.79 for this data set. Of course, some trend is expected since roughly 30--40% of the total Salmon Population is chinook; the question is, what is the dispersion in total salmon counts that results from using chinook as the tracer?
The formal fit is:
This means that chinook counts can be used to predict the total Salmon counts to an accuracy of 97,000. Since the Salmon count ranges from 500,000 to 1 million, that means an accuracy of 10-20%. This suggests that, if you are only interested in total Salmon, you can use chinook as a reliable tracer, provided that you don't require accuracy better than 20%.
The fit as applied to the data is shown here. In this case, r =0.79 and the fit is a good fit. There are no strongly abberant data points.
And so after this evolution we arrive at a crossroads, strongly
driven by non-equilibrium growth, and we look for solutions about
how to better manage the planet.
Much of the current dialogue in environmental studies or management
needs to shift away from belief to a position of knowledge.
The acquisition of knowledge requires gathering good data, analyzing
it correctly, and then forming new questions on the basis of the
Much of the current dialogue in environmental studies or management needs to shift away from belief to a position of knowledge. The acquisition of knowledge requires gathering good data, analyzing it correctly, and then forming new questions on the basis of the data.
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