## Results
### Answers to Research Questions
It shows that the literature provides mostly the evaluation based studies (85%), followed by validation (10%) and experience (5%). This means that the studies are usually Evaluation studies (like empirical research including literature surveys, case studies etc.). Further the evaluation approaches in the form of solutions validated in the industrial real scenarios are also too limited. Validation based studies (solutions validated in laboratory settings) are very limited. The literature lacks the philosophical, opinion and experience papers, that could otherwise be very helpful to the startup team as the necessary guidelines to be adopted in their working context. Such guidelines are driven from the experiences that the practitioners gained in their companies and thus are useful lessons that could be useful to the startup team members for avoiding mistakes and improving their success rates. Table 7 gives the frequency of research classified on basis of contribution (outcomes) and it specifies that outcome of 65% studies is the theory, followed by 20% conceptual models/frameworks and 10% methods and 5% lesson learned. \begin{table}
\begin{tabular}{c c} \hline \hline
**Research Type** & **Number of Studies** \\ \hline Evaluation & 17 \\ Validation & 02 \\ Solution & 00 \\ Philosophical & 00 \\ Opinion & 00 \\ Experience & 01 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Number of studies classified on basis of research type. \begin{table}
\begin{tabular}{c c} \hline \hline
**Requirement Engineering Activities** & **Number of Studies (Contribution)** \\ \hline Requirement Elicitation & 3.5 (_Decimal signifies joint focus_) \\ \hline Requirement Prioritization & 01 \\ \hline Requirement Documentation & 01 \\ \hline Requirement Validation & 2.5 (_Decimal signifies joint focus_) \\ \hline Product Validation & 04 \\ \hline Requirement Engineering & 08 \\ (_Focus on Generic Requirement Engineering_) & 08 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Research Focus on Requirement Engineering Activities. Figure 2 shows that the researcher's focus across different requirement engineering activities is non-uniform. There is much focus on generic requirement engineering in the past five years. Requirement elicitation had been focused in 2017 and 2019 but the quantitively the focus is declining. Software documentation and requirement prioritization are least focused activity while the former got attraction in 2017 and later got attention in 2018. The less focus on software documentation may be because startups have high pressure to release as early as possible to the markets under limited resources, that leads to neglection of this activity. Requirement prioritization seems to be an informal process in startup contexts where the subjective judgements of the startup team based on their interactions with the customers, is used to identify the higher priority features for next release (or MVP). Product validation and generic requirement engineering has been much focused in the past two years (2019 and 2020). Requirement validation is again gaining attention of the researchers. Figure 3 shows that there had been much focus of researchers to undertake research regarding requirement engineering to attain a good product/market fit and growth. The focus had been much higher since 2017 (60% studies) and the total focus being 62.5% since 2016. The researcher's attention to studying the existing processes and innovating them, seems to be reducing with the time. Lack of studies reporting the improvements may hinder the ability of startups to adopt the best recommended practice as per their working contexts. **RQ 4**. : _What could be possible underlying research challenges that are addressed by the researchers (at an abstract level)?_  
The underlying motivations of the studied research papers are extracted after carefully analysing the abstracts of the studies.