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I am very confused about what kind of statistical test to use in RStudio on my project,

I have measured the mean salinity for 3 levels of population density (low medium and high) across 6 months (therefore 6 mean values per population density level)

I want to see if there is a statistical significance between the mean Salinity value (Quantitative continuous data) and Population Density (categorical; low, medium, high) but I'm not sure which test to use I have tried both Friedmans & Kruskal-wallis but not sure which to use.

Many Thanks for any advice!

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  • $\begingroup$ For clarification, you have data for month 1, month 2, etc to month 6? Are you interested in change over time or just if there is a difference between the population levels? $\endgroup$
    – N Brouwer
    Commented May 11 at 22:33
  • $\begingroup$ Hiya I have data for 6 monthes, but this was only to increase the size of my data set , i am more interested in the differnece between the population levels in order to accertain whether a preference in distribution is show to differnent salinity levels! $\endgroup$
    – Willa
    Commented May 12 at 10:39
  • $\begingroup$ One more question - how many replicates do you have of each population density? You say "I have measured the mean salinity for 3 levels of population density" did you measure salinity in one place with low density and take the mean of the measurements for six months , or do you have the more than one place with low population density and take the mean at month one, months 2, etc. ? ( also what is varying at the different populations? A plant?) $\endgroup$
    – N Brouwer
    Commented May 12 at 13:54
  • $\begingroup$ hey thanks for the reply, so the data was extracted from qgis maps that I made, a kernal density heatmap was made of the distribution of sharks I'm looking at for a whole month, eg. january. I then split the heatmap into three sections containing low medium and high density, once split I extracted the mean salinity from the overlapping area of each density. so I have separate mean salinity values for low, medium and high. this was repeated for the other 5 months so I have 18 mean values into with 6 values in each density level. hope this is what you mean? $\endgroup$
    – Willa
    Commented May 12 at 15:22
  • $\begingroup$ I also extracted the SD, range and count if this helps? $\endgroup$
    – Willa
    Commented May 12 at 15:25

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