further work on introduction

main.bib

@@ -2221,3 +2221,24 @@ Based on {WST} and {HR} data from the wearable device, the algorithms demonstrat
 	langid = {english},
 	file = {PDF:/home/alex/Zotero/storage/J9ITWN5R/Owen - Physiology of the menstrual cycle.pdf:application/pdf},
 }
+
+@article{earle_use_2021,
+	title = {Use of menstruation and fertility app trackers: a scoping review of the evidence},
+	volume = {47},
+	issn = {2515-1991, 2515-2009},
+	url = {https://jfprhc.bmj.com/lookup/doi/10.1136/bmjsrh-2019-200488},
+	doi = {10.1136/bmjsrh-2019-200488},
+	shorttitle = {Use of menstruation and fertility app trackers},
+	abstract = {Introduction There has been a phenomenal worldwide increase in the development and use of mobile health applications ({mHealth} apps) that monitor menstruation and fertility. Critics argue that many of the apps are inaccurate and lack evidence from either clinical trials or user experience. The aim of this scoping review is to provide an overview of the research literature on {mHealth} apps that track menstruation and fertility.
+Methods This project followed the {PRISMA} Extension for Scoping Reviews. The {ACM}, {CINAHL}, Google Scholar, {PubMed} and Scopus databases were searched for material published between 1 January 2010 and 30 April 2019. Data summary and synthesis were used to chart and analyse the data.
+Results In total 654 records were reviewed. Subsequently, 135 duplicate records and 501 records that did not meet the inclusion criteria were removed. Eighteen records from 13 countries form the basis of this review. The papers reviewed cover a variety of disciplinary and methodological frameworks. Three main themes were identified: fertility and reproductive health tracking, pregnancy planning, and pregnancy prevention.
+Conclusions Motivations for fertility app use are varied, overlap and change over time, although women want apps that are accurate and evidence-based regardless of whether they are tracking their fertility, planning a pregnancy or using the app as a form of contraception. There is a lack of critical debate and engagement in the development, evaluation, usage and regulation of fertility and menstruation apps. The paucity of evidence-based research and absence of fertility, health professionals and users in studies is raised.},
+	pages = {90--101},
+	number = {2},
+	journaltitle = {{BMJ} Sex Reprod Health},
+	author = {Earle, Sarah and Marston, Hannah R and Hadley, Robin and Banks, Duncan},
+	urldate = {2025-08-04},
+	date = {2021-04},
+	langid = {english},
+	file = {PDF:/home/alex/Zotero/storage/XMT448BI/Earle et al. - 2021 - Use of menstruation and fertility app trackers a scoping review of the evidence.pdf:application/pdf},
+}

thesis/main.tex

@@ -3,6 +3,7 @@
 
 % Preamble
 \documentclass[a4paper, 12pt]{article}
+\usepackage[utf8]{inputenc}
 
 % Packages
 \usepackage{amsmath}

thesis/sections/introduction.tex

@@ -4,26 +4,23 @@
 
 \section{Introduction}\label{sec:introduction}
 
-In textbooks, a menstrual cycle is 28 to 30 days in length with its ovulation happening around day 14~\cite{Phy}
+While textbooks often describe a menstrual cycle as lasting 28 to 30 days with ovulation around day 14~\cite{owen_physiology_nodate},
+such regularity is the exception rather than the rule~\cite{munster_length_1992, bull_real-world_2019}.
+For individuals with consistent cycle patterns, simple calendar-based predictions may suffice.
+However, for the majority, especially with increasing age and associated irregularity, more sophisticated methods are necessary.
+This, combined with an ever higher age of pregnancy in industrialized and industrializing countries,
+underscores the growing need for accurate understanding of the menstrual cycle~\cite{sauer_reproduction_2015}.
 
-
-
-The average age of pregnant women in developed countries has been increasing over the past few decades.
-Combined with the sharp decline in conception rates after age 35,
-this trend underscores the growing need for accurate understanding of the menstrual cycle~\cite{sauer_reproduction_2015}.
-Predicting the fertile days in a women's menstrual cycle is not only relevant for family planning but also for
-natural contraception and general health monitoring, as the corresponding hormone levels have a significant impact on
-the overall health and well-being of a woman.
-
-Textbook cycles usually have a length of 28 days with an ovulation around day 14.
-This however, does not represent the real world variability of menstrual cycles.
+For many women, the practical use cases of menstrual cycle monitoring are \emph{Natural Family Planning} (NFP) and contraception~\cite{earle_use_2021}.
+For these use cases, it is essential to identify the ovulation and its corresponding fertile and infertile days in a cycle,
+to either avoid or achieve pregnancy more effectively.
 
 Ovulation is the process in which an egg cell is released from the ovaries, making fertilization possible.
 This process is regulated by hormonal changes, including fluctuations in luteinizing hormone (LH) and
 follicle-stimulating hormone (FSH), and is accompanied by other physiological changes such as an increase in electrical resistance
 and viscosity of the cervical mucus or an increase in body temperature~\cite{wallach_prediction_1980}.
-These processes remain incompletely understood and are influenced by lifestyle factors such as stress, diet or exercise or
-health-related factors such as Polycystic Ovary Syndrome (PCOS), making ovulation difficult to predict.
+These processes remain incompletely understood and are influenced by lifestyle factors such as stress, diet, exercise,
+or health-related conditions such as Polycystic Ovary Syndrome (PCOS), making ovulation difficult to predict.
 
 In theory, these physiological changes provide a basis for predicting ovulation and the surrounding fertile window.
 In practice, however, many of these signals are difficult to measure continuously, as they require invasive procedures,
@@ -35,7 +32,7 @@ others suggest its predictive value for ovulation~\cite{sato_novel_2024, royston
 
 However, most existing studies rely on small, idealized datasets that exclude cycles with irregular lengths or late ovulation.
 While such restrictions simplify the prediction task and yield high accuracy, they give a misleading impression of real-world model performance.
-It is thus not yet fully clear, whether temperature can reliably be used as a predictive marker for ovulation or fertility.
+It is thus not yet fully clear whether temperature can reliably be used as a predictive marker for ovulation or fertility.
 
 Additionally, other studies have focused on peripheral temperature measurements of skin or in-ear temperature,
 which are subject to many sources of noise that can significantly affect the quality of the resulting predictions.
@@ -43,24 +40,19 @@ Intravaginal temperature reflects true core body temperature and offers higher r
 as it is largely unaffected by external circumstances.
 This allows for more reliable detection of subtle thermal shifts associated with ovulation, especially in irregular cycles.
 
-Generalization is critical for reliable ovulation prediction,
-especially given the high variability in cycle patterns~\cite{munster_length_1992, bull_real-world_2019}.
-This is particularly relevant in high-stakes applications such as natural contraception or in-vitro fertilization (IVF),
-where inaccurate predictions can have serious consequences.
-
-
-This study aims to advance ovulation prediction by leveraging an extensive database of more than 40,000 menstrual cycles recorded using
-an intravaginal wearable device that continuously measures core body temperature.
+This study aims to advance fertility prediction by leveraging an extensive database of more than 40,000 menstrual cycles,
+covering cycle lengths 11 to 149 days and ovulation days ranging from 7 to 136, recorded using
+an intravaginal wearable device that continuously measures core body temperature at a resolution of 288 measurements per day.
 The objective is to develop a machine learning model that performs reliably across diverse cycle types, including irregular ones.
 To this end, we compare a set of time series-based machine learning architectures and evaluate their performance for
-natural family planning and contraception.
+NFP and contraception.
 Finally, we demonstrate that high predictive accuracy on highly regular, curated datasets, as commonly reported in prior work,
-does not reflect general applicability, since such datasets tend to favor even simple, rule-based approaches.
+may overestimate real-world applicability, since such datasets tend to favor even simple, rule-based approaches.
 
 
 The research objectives are:
 \begin{itemize}
+    \item To evaluate the predictive value of body temperature for ovulation and fertility across diverse menstrual cycle types.
     \item To assess the performance of different model architectures on the use cases of natural family planning and contraception, across both regular and irregular cycles.
     \item To compare sophisticated machine learning models with simple rule-based baseline approaches.
-    \item To study the overall predictive quality of temperature for ovulation and fertility prediction.
 \end{itemize}