Thread: Which statistical test for comparing two rates?

I have data for the rate of photosynthesis for two species for my biology A level coursework, I am required to do a statistical test to show significance but I'm unsure of a test for comparing two rates. Any advice would be appreciated, thanks.

Do you mean two rates as in two average numbers, one for each species? The type of test you can use may depent on some particular properties of your data. For example, are variances equal and is your 'rate of photosynthesis' normally distributed? If this is the case, I think an 'independent t-test' as well as an 'ANOVA' will work. Both compare two mean values, but since ANOVA is mostly used when multiple t-tests are required I think an independent t-test will do the job. Think you can work with this?

Originally Posted by seignet

Do you mean two rates as in two average numbers, one for each species? The type of test you can use may depent on some particular properties of your data. For example, are variances equal and is your 'rate of photosynthesis' normally distributed? If this is the case, I think an 'independent t-test' as well as an 'ANOVA' will work. Both compare two mean values, but since ANOVA is mostly used when multiple t-tests are required I think an independent t-test will do the job. Think you can work with this?

The data I have for each species is for a rate as in an accumulated value of total oxygen output for every 1 minute up to ten minutes.

Hi jblox,

First calculate the rate of photosynthesis for each species, using your raw data on Oxygen output, then perform an unpaired t-test to see if there is a significant difference in photosynthesis rate between the two species.

http://www.marietta.edu/~spilatrs/biol103/photolab/photosyn.html

http://en.wikipedia.org/wiki/T_test


Best wishes,

Tridimity

P.S. I think this is correct, but please check with someone else before you take my word for it, since it's actually quite important that you get this right!

Do you mean like this?

species A: V1; V2; V3; V4; V5; V6; V7; V8; V9; V10
species B: V1; V2; V3; V4; V5; V6; V7; V8; V9; V10

What exactly do you want to know? The difference between each V-pair (V1A compared to V1B, V2A compared to V2B etc.)? Or the difference between oxygen output/minute in A compared to oxygen output/minute in B? For the latter, you can simply calculate both rates (devide V10 by ten) and use an independent t-test to compare.

Originally Posted by seignet

Do you mean like this?

species A: V1; V2; V3; V4; V5; V6; V7; V8; V9; V10
species B: V1; V2; V3; V4; V5; V6; V7; V8; V9; V10

What exactly do you want to know? The difference between each V-pair (V1A compared to V1B, V2A compared to V2B etc.)? Or the difference between oxygen output/minute in A compared to oxygen output/minute in B? For the latter, you can simply calculate both rates (devide V10 by ten) and use an independent t-test to compare.

Ok, so I have my rates, but what formulas do I need to use? I can seem to find any usefull T-test tutorials.

Yes, it would be most informative to compare the overall photosynthesis reaction rates between the two species, rather than trying to compare the individual Oxygen outputs at each time point.

This Wikipedia link provides some information on how to perform an independent (unpaired) t-test - see section 5.3: Student's t-test - Wikipedia, the free encyclopedia

Scroll down to section 6 for worked examples.

Best wishes,

Tridimity

Oh, and if you have access to SPSS, you can enter your data and perform an unpaired t-test via Analyse > Compare Means > Independent Samples t-test

I have sorted it now. Thanks to everyone that helped out.