Whistler Reporting Rates

Subject: Whistler Reporting Rates
From: "David McDonald (personal)" <>
Date: Thu, 26 Apr 2012 21:01:24 +1000
Hmm, good questions, but these data are not samples from a known population, so sample size is irrelevant. Perhaps better to think of them as purposive data collecting, it is definitely not a sample survey strategy.

You ask about statistical reliability. I suspect that reliability is high (fairly consistent data collection methods) but a better question is about the statistical validity of the data (to what extent do they represent the reality of what is being measured).

Cheers - David

On 26/04/2012 6:42 PM, Kevin and Gwenyth Bray wrote:
At risk of being (pretty rightly) accused of getting involved in something about which, in detail, I know very little (I'm a very amateur bird-watcher, though I do have qualifications in science and economics of some relevance to the question I'm asking!), I would be interested to know something about the statistical "reliability" of the data shown in the last few days on rufus and golden whistler population time series trends and population seasonalities.  My sense is that only if the data are statistically sound can reasonably reliable general conclusions be inferred from them.  (I'm not for one moment suggesting there is a "reliability problem" - it's just that I've not seen any comment on the question, either way).
I am wondering (a)  what sample sizes are these data based on - essentially how many actual bird sitings and how many "nil" sitings from how many observation sites/areas are represented by each data point on the graphs; and (b) what proportion of the "area/region of interest"  (eg, the ACT if it's trends in the ACT that are being reported)  - or perhaps more usefully what proportion of the species' typical habitat' in (say) the ACT, was included in the aggregate data?
I ask these questions, in part due to prior experience in ostensibly scientific data and analyses on Southern Bluefin Tuna (SBT) population, when I was involved as a policy adviser in trying to interpret the analyses from what had turned into a major dispute between Australian and Japanese fish population scientists over SBT populations and "responsible" fishing quotas. 
To simplify the detail of the analysis, the dispute turned on significant differences in the two countries' scientists' methodologies in estimating (and projecting) current and future SBT populations.  In part, an element in the different analyses and conclusions was the extent to which  population data from a set of "sample areas" which necessarily covered only a small proportion of the total range of SBT could, or could not, be regarded as "representative".
So, to put my questions that way, can you be confident that the whistler (both species) sample areas used in the data/analysis that have are now being presented and discussed are "representative" enough , and the number of sitings made (whether positive or not) large enough to enable reliable inferences to be drawn?
Thank you.
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