IgG concentration in tissue cell culture serum

Taken from this site.

What about inductive and deductive reasoning?

Inductive and deductive reasonings (see also abductive reasoning) are two ways to come up with an idea/conclusion. The process is called inference. 
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In inductive reasoning, we start off with a set of specific answers to specific questions and try to generalise these data to an idea/conclusion. It infers b (probable relation) from a (specific observations) often by persuasion.
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In deductive reasoning, we already have a set of general data. We try to glean meaning/conclusion from these data. It infers b (logical consequence) from a (assumptions of truth).
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References
1. https://en.m.wikipedia.org/wiki/Abductive_reasoning

Relationship between variables: correlation/association and causation

Hypothetical questions involve variables (or assigned variables). Hypotheses test the relation of these variables. There are two main types of relation: correlation/association and causation.
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Causation is more difficult to test as compared to correlation/association. In clinical trials, controlled experiments are designed to test causation whereby sampling of a population produces treated and untreated groups and the hypothetical question is whether a treatment will cause specified response. The variables are therefore (1) treatment and (2) response, whereby the sample is assumed to be similar.
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Several good reviews on the subject are the following:
1. https://www.psychologytoday.com/blog/all-about-addiction/201003/correlation-causation-and-association-what-does-it-all-mean