## 3 Research Methodology
### Threats to the Validity of the Experiment  
Regarding the analysis of threats to the validity of the study, the experiment conducted corresponds to four instances of the 'Pretest and posttest with one experimental group only' typology [48]. The experiment does not consider a control group because this would have required involving a set of start-ups that would not have participated in any of the activities organised in the acceleration programme but would have been subsequently evaluated to check their evolution. The acceleration programmes did not consider this option. Next, we describe the main threats to the validity of this type of experiment according to [PERSON] and [PERSON] [48] and comment on the impact they may have had on the results and conclusions of the study:  
* The _History_ effect refers to those events or factors that occur while the experiment is in progress and that are beyond the control of the experiment designer. Given the complexity of the objective of the experiment (to test the impact of COVID on the performance of start-ups participating in acceleration programmes) and the heterogeneity of the participants (business experience, level of education and network of contacts of the founders, technology used, level of income and maturity of the start-ups, etc. ), it is very difficult to assess the impact of this effect on the validity of the results. This is precisely the objective of the statistical tests described in the previous section: to verify that the evolution of the indicators of the start-ups has been similar in all cases and that, therefore, regardless of the events that may have taken place while the experiment was underway, all participants have experienced a similar evolution after their passage through the acceleration programme. * _Maturation_ refers to how the passage of time and the experience participants gained in the programme can affect the outcome of the experiment. Since there is no control group, it is not possible to assess the effect of this threat directly. Again, the objective of the statistical tests is to check that the evolution of the indicators is independent of what has happened during the acceleration programme and is similar for all start-ups, in order to mitigate the effect of this threat. In addition, almost all start-ups had already participated in previous acceleration programmes, where they started the development of their business idea. Therefore, they had already acquired some of the knowledge that can be gained as part as their participation in an acceleration programme, so it is possible to assume that the maturation effect had already occurred to a large extent for almost all of them. * _Main testing_ and _interactive testing_ effects occur as a result of participants being tested on entry and exit from the acceleration programme and affect participants' posttest scores. This may be due to factors such as participants not understanding the questions well or not having experience with the scale used, wanting progress to be visible after the programme, paying more attention or trying harder knowing that they are being assessed, etc. In this sense, it has to be clarified that, from the beginning of the acceleration programme, it was indicated to participants that the purpose of the evaluation was to make them aware of their current status, of what goals they would have to achieve to improve in each of the 30 business-oriented indicators and of the progress they had experienced after their passage through the programme. In any case, to mitigate this effect, the scores given both at the beginning and at the end of the acceleration programme were agreed between the start-up and the IoT Tribe team. In this way, an attempt was made to maintain homogeneity in the evaluation. * _Mortality_ refers to the impact of participants dropping out of an experiment. In the case of the two acceleration programmes studied, only one start-up did not complete each of the programmes, which represents 5.26% in the pre-COVID programme and 4.76% in the into-COVID programme.