Question: Repeated Measures or Not
gravatar for ab123
24 months ago by
ab12340 wrote:

Hello there,

Quick conceptual question over whether this experiment truly would reflect a repeated measure or whether samples are indeed independent.

I have a cell culture that is grown in 5 different flasks to produce 5 biological replicates. These are then split further into 10x 6-well plates (3 tech reps which are later pooled) and exposed to 5 doses (including control). Now, for each dose (e.g. 1ug/ml, 2, 3, 4, 5) I get 5 bioreps.

My question is: is dose 1ug/ml in biorep 1 independent from 2ug/ml biorep 1, given that they are grown on different well plates or does this really count as repeated measures?

If I can grow cells in a flask to represent biological replicates, then wouldn't growing them further in different well plates also represent biological independence?

Thank you!

ADD COMMENTlink written 24 months ago by ab12340

I am not sure I understand the design. What's the point of having replicates if you pool them ?
It seems that you have 5 flasks each treated with 5 doses. This is not a repeated measure because the doses were not applied sequentially to the flasks but instead to a (presumably) independent sample from each flask. The notion of biological replicates is misleading here. In the end, you have 5 replicates of each drug treatment and each replicate includes all sources of variability in the experiment.

ADD REPLYlink written 24 months ago by Jean-Karim Heriche22k

You forget that the flasks are plated in 10x 6-well plates, so you are spreading out the bio reps. Ignore the tech reps within these plates, they are not important here > they're merely for biomass. I.e. Biorep 1 is exposed to 5 doses across say 5 well plates.

ADD REPLYlink modified 24 months ago • written 24 months ago by ab12340

This is how I understood it. It's just as if you'd done the same experiment 5 times. Repeated measures are when you apply the different treatments to the same sample. This would be the case here if you applied all doses to the same well. Since you're using a different sample of cells for each dose, you can treat them as independent.

ADD REPLYlink written 24 months ago by Jean-Karim Heriche22k

Ah, thank you. So you're saying the doses themselves are independent. So if I apply dose 1ug/ml, 2, 3, 4, 5 to Biorep 1, then these are independent as well.

ADD REPLYlink written 24 months ago by ab12340
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