Appendix A — Question, Objective and Hypothesis

A.1 Overview

This document provides a detailed outline of the thesis’s research question, objective, and hypothesis.

A.2 Question

Every scientific inquiry should be guided by a central question. For this study, the guiding question is:

Is latitude associated with chronotype?

A.3 Objective

The primary objective is to model and test the hypothesis underlying this question within the context of human circadian rhythms, by critically assessing whether there is a meaningful association between latitude and circadian phenotypes in the Brazilian population.

A.4 Hypothesis

To address the research question, the study employs Popper’s hypothetico-deductive method. This approach is structured as follows:

Figure A.1: Simplified schema of Popper’s hypothetico-deductive method. 
flowchart LR
  A(P1) --> B(TT)
  B --> C(EE)
  C --> D(P2)

Here \(\text{P}_1\), is the problem from which we start, \(\text{TT}\) (the ‘tentative theory’) is the imaginative conjectural solution which we first reach, for example our first tentative interpretation. \(\text{EE}\) (‘error- elimination’) consists of a severe critical examination of our conjecture, our tentative interpretation: it consists, for example, of the critical use of documentary evidence and, if we have at this early stage more than one conjecture at our disposal, it will also consist of a critical discussion and comparative evaluation of the competing conjectures. \(\text{P}_2\) is the problem situation as it emerges from our first critical attempt to solve our problems. It leads up to our second attempt (and so on) (Popper, 1979, p. 164).

The central hypothesis of this study, as outlined in Chapter 1, is:

Hypothesis
Latitude is associated with chronotype distributions, with populations closer to the equator exhibiting, on average, a shorter or more morning-oriented circadian phenotype compared to those residing near the poles.

This hypothesis is grounded in early discussions in chronobiology and is supported by numerous studies, including: Bohlen & Simpson (1973); Pittendrigh et al. (1991); Roenneberg et al. (2003); Randler (2008); Hut et al. (2013); Leocadio-Miguel et al. (2017); Randler & Rahafar (2017).

To evaluate the hypothesis, the study adopts an improved approach to Null Hypothesis Significance Testing (NHST), rooted in the original Neyman-Pearson framework for data testing (Neyman & Pearson, 1928a, 1928b; Perezgonzalez, 2015). The hypotheses are formally stated as follows:

\[ \begin{cases} \text{H}_{0}: \text{Latitude is not associated with chronotype} \\ \text{H}_{a}: \text{Latitude is associated with chronotype} \end{cases} \]