ESTRUCTURA DE LA OPERACIÓN a) Patrimonio del fideicomiso

The Altenburg review demonstrated that there is a need for more larger scale randomised controlled-trials (RCTs) evaluating SB interventions in children. There are a number of different factors that can impede the evaluation of a large-scale trial such as inadequate compliance, intervention delivery, recruitment and retention. To maximise the evaluation process, it is important that preliminary studies are undertaken to identify and minimise such potential issues (164). Researchers are encouraged to publish preliminary work in advance of main trials (165). Such preliminary research is usually labelled as a pilot and/or feasibility study; however, these terms are often used inconsistently and inter-changeably (166) but have some distinctions that warrant discussion. Preliminary studies of large-scale complex intervention trials with several modes of ‘treatment’ may be particularly susceptible to these inconsistencies as the different stages of trial development are less well defined and clear cut (165). Nevertheless, review studies of preliminary research have attempted to define and distinguish pilot and feasibility studies using study methodologies, with the consistent conclusion that differences between the two are generally not clear (167,168).

Feasibility can be broadly described as a study designed to assess whether a larger or full-scale study is possible (can it be done?) (165). The Nation Institute for Health

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Research Evaluation, Trials and Studies Coordinating Centre (NETSCC) states that important parameters should be estimated for a main trial such as the number of eligible participants, willingness of participants to be randomised, response rates, follow up rates, adherence rates, time required to collect and analyse data and willingness of relevant individuals to support the intervention (169).

A pilot study has been described as a miniature version or “scale model” of a main trial to explore if and how the main components of the study all combine together (164,169). The term ‘pilot’ is relevant in that an intervention or application of an intervention is novel (165). The main uncertainties established during trial development should be addressed and amended before a full-scale trial is undertaken (164,170). A pilot should focus on the processes of running a main trial (e.g. recruitment, treatment, randomisation, follow- up assessments), providing training and experience of the main trial (165). Pilot studies have been used to help establish a sample size calculation for a later main trial (167), however, pilots usually have small samples which offer inherent imprecision; a meaningful effect size estimate is not provided and therefore this practice is not advised (165,167).

Despite attempts to define and clarify pilot and feasibility studies, such studies are often poorly reported (167) and there remains much confusion around the terms (165). Furthermore, studies may be labelled as a feasibility or pilot study correctly or incorrectly depending on the definition used (165). There appears to be some consensus that mutually exclusive definitions of pilot and feasibility studies cannot be applied (171). Nevertheless, in a recent review of current practice and editorial policy, Whitehead et al. (165) concluded that pilot studies are consistently distinct from feasibility studies by:

- Using more strict study methodology - Having a plan for further work

- Focusing on trial processes

- Being a smaller version of a main trial

A more flexible methodology has been ascribed in part to pilot studies often being a miniature version of a main study and therefore some outcomes will be specifically designed to inform this trial (165,167). Conversely, a feasibility study can be an isolated study (165). A plan for further work from a pilot study is crucial because otherwise these studies may be underpowered, unethical and therefore provide limited scientific use

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(165). Some pilot studies do perform hypothesis testing (167), however, in this instance, a control arm is required (167) and since pilots are often not sufficiently powered to test effectiveness, the findings should be reported cautiously (164,172).

Pilot studies may test the feasibility of a larger study and therefore it could be argued that a pilot study is also a feasibility study (165). In fact, within a recently developed framework attempting to define pilot and feasibility studies, it specifically states that pilot studies are a subset of feasibility studies (171). However, the inverse cannot be said of feasibility studies being pilot studies (165) since feasibility studies may be conducted in isolation. Whitehead et al. (165) suggest that “a pilot study is a special type of feasibility study which has a plan for further work and mimics the envisioned definitive trial.” Whitehead et al. also concluded that attempting to define a feasibility study may be futile since all preliminary work could be described as ‘feasibility’. Conversely, Arian et al. (167) suggest that despite varying definitions between health research funding bodies, authors should be aware of the different requirements of pilot and feasibility studies and report them appropriately, with a recommendation to use the NETSCC definitions. Eldridge et al. (171) stated that three distinct study types make up feasibility studies; randomised pilot studies, non-randomised pilot studies and feasibility studies that are not pilot studies. The latter involves research attempting to understand whether an aspect of an intervention to be evaluated can be done without actually implementing the intervention within a preliminary study (171). Eldridge et al. also suggest that researchers should consider feasibility as an overarching concept and that all studies conducted with the objective of informing a main trial are a feasibility study (171). With an expected increase in complex interventions in future trials (164,168), and the recommendation from the MRC that preliminary studies are conducted before main trials, it is important that researchers carefully consider the different definitions and characteristics of feasibility and pilot studies, clearly reporting their reasons for adopting such criteria.

When designing an intervention, including during pilot and feasibility phases, it is important to consider the behaviour change theory in which to underpin the intervention. The following section explores the theories, models and frameworks that have been previously applied to SB and their suitability.

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1.12.2. Behaviour change theory, sedentary behaviour and sedentary behaviour