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I have records (presence) for an invasive species, from opportunistic data for 10 years, less than 10 records for each year. I have calculated distances form watercourses, % of land use in buffers and elevation.

I want to compare these variables to see if there are differences between the years. What test can I use? I don't think I can use pseudo-absences. By saying opportunistic I mean that the records were accidental sightings, not collected in the framework of a systematic sampling.

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    $\begingroup$ If "opportunistic" means what it sounds like -- a sample of convenience, not necessarily representative -- then no statistical test is applicable. But if the data were collected systematically (perhaps by monitoring a set of locations regularly over time) then there's much you can do, depending on what you mean by "compare these variables." Could you edit your post to elaborate on these points? $\endgroup$ Commented Nov 22, 2020 at 21:35
  • $\begingroup$ as I added in the question, the data were accidental sightings $\endgroup$ Commented Nov 22, 2020 at 21:55
  • $\begingroup$ I thought to use ANOVA, would it be too wrong? $\endgroup$ Commented Nov 22, 2020 at 22:04
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    $\begingroup$ ANOVA can be useful for exploring the data. You're likely better off concentrating on finding useful ways to visualize them, though. $\endgroup$ Commented Nov 23, 2020 at 14:44
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    $\begingroup$ thank you for your time, I think this is the most useful advice $\endgroup$ Commented Dec 4, 2020 at 14:08

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Answered in comments by whuber

If "opportunistic" means what it sounds like -- a sample of convenience, not necessarily representative -- then no statistical test is applicable.

and

ANOVA can be useful for exploring the data. You're likely better off concentrating on finding useful ways to visualize them, though.

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