The data obtained for this research show that older people had less similar free lists, thus reducing the double presence of species between the lists. This indicates that even in the face of a relatively short interval (three months), as proposed in this research, elderly people may have trouble efficiently recalling the names of plants they know.
In ethnobiological research, age is identified as a factor that influences traditional botanical knowledge . When comparing the data obtained for this research with that of the literature, there is a disparity of results in relation to studies that report on the influence of age on knowledge about medicinal plants. Studies point out that it would be best to collect data from older people, as they generally have greater knowledge about natural resources. Thus, they are considered to have knowledge about medicinal plants, both for their ability to retain it throughout life, derived from lived experience , and due to the frequent use they make of them , which is related to the number of plants that are cited in a free list, for example. These works end up restricting comparisons between individuals of different generations [41, 42, 43].
It is important to note that this study compared the similarity of cited species and as there was a time interval from one free list to another, it is necessary to consider that the difference between the lists may be due to something temporary in these individuals. Even with this observation, the result of this research indicates the need for greater caution regarding the collection and analysis of information from this individual knowledge, especially when related to this age group, in order to avoid bias in the results.
A possible justification for presenting different free lists in this study is due to a characteristic inherent to older people: impaired memory. Some researches claim that elderly people are more forgetful than young people [18, 44] and attribute this forgetfulness to findings in which recorded knowledge begins to decline after the group aged between 59 to 68 years . Thus, the interviewees of this group do not remember all the medicinal plants they know, needing more effort to remember, which brings limitations in the answers.
In these cases, it cannot be affirmed precisely that a greater number of plants mentioned by one participant represents greater knowledge in relation to another participant who mentioned fewer plants. Thus, in communities with elders, it is necessary to avoid evaluations that consider individual knowledge, based only on the number of plants mentioned in a single free list.
It is suggested the use of more than one free list, with the same participants, in communities with high rates of elderly people. This will help to collect more complete data about plants known to this age group and will help to validate individual knowledge, thereby improving the quality of the data collected. Another suggestion would be to opt for the interview-checklist , a technique that provides more stimulus to the interviewee and provides less memory effort in relation to the free list. In addition, it allows the interviewee to be more comfortable and makes it easier to remember the question. Wiryono et al.  recorded the correlation between botanical knowledge and people's age. The authors observed that when using photographs to identify known plants within a community, the elderly recognize more plants and better report their respective uses in relation to younger people. However, there is still a few studies that link age and the use of visual stimuli, requiring further testing for this statement.
In view of the context presented above on the influence of age on the collection of ethnobiological data, the researcher who is aware of this approach will be able to identify the technique that best suits their research, and it is up to them to select the best data collection instrument to capture the desired information.
Do external stimuli influence the content of free lists?
Regarding the different places where the interviews were conducted, our results show that it did not interfere with the plants cited. In contrast, the study by Miranda et al.  reported that the place where the interview is conducted has a direct influence on the responses mentioned by the interviewees, in which the participants listed the plants according to the local context in which the interviews were conducted. Thus, ethnobiological studies suggest that the presence of environmental stimuli during the execution of free lists presents a limitation to the method, as the participants can be influenced by them at the time of the interview.
As in the present study, where the interviews were conducted with non-specialists and with native vegetation occurring close to the residences, the interview location was also studied in southeastern Madagascar. That study found that the proximity of the participants’ house to the forest had no influence on the medicinal plants mentioned . In this rural Brazilian community, interviews were conducted in closed and in open spaces, where in the latter the participant had visual contact with nature and yet location did not interfere with list’s content of the free lists. However, studies need to be repeated in other communities to understand if these results represent a general pattern.
In ethnobiological research, interviews can take place in various environments, such as, at the participant’s home, close to home, at the workplace, among others and in living spaces. Among those, the living space is the least suitable in opposition to the other places, where the participants have a greater control of the spaces  and feel more comfortable. In addition, a quiet place, away from the areas of greatest activities should be prioritized . In the studied community, the interviews were conducted at the participant's house, the neighbor's house and at the workplace (within the community), a very familiar environment and perhaps that is the reason the place has not influenced on the collection of information, as the selected space prepares a relaxed and enjoyable environment for the interview.
Regarding the presence and interference of third parties, studies with married couples have found that the presence of the spouse affected participant’s responses, either because the partner’s presence brought positive evaluations about the marriage or because a spouse had to agree with the partner, making disclosure of negative or conflictiong positions difficult [47,48]. It is recommended that studies aimed at assessing individual knowledge conduct one-to-one interviews. Yet there are still no ethnobiological studies that address the influence of a third-party presence or interference of a third person in ethnobiological studies.
Other studies suggest that the presence of third parties may interfere in the results. This may happen at the moment when responses are suggested to the interviewee, impairing the data collection, since the items must be said by the interviewee in the order that comes to their mind . Thus, the presence of a third person should be avoided , although sometimes it is not possible to prevent it. In this study, it was found that the interference of third parties did not influence on the collection of information.
The existence of a third person had an opposite effect to the expected, positively influencing the similarity of the two lists obtained, increasing the double presence of items and allowing the participants to remember the same plants reported in both free lists. This demonstrates that despite the fact the researcher is a stranger in the community, there is the possibility of causing a certain discomfort and shyness during the interview, which could exert influence on the free list. However, the presence of a known person (friend or relative) during the interviews was positive and made the participant feel more comfortable, making the family environment pleasant and safe to mention what they know about medicinal plants. The presence of another person during the interview may have caused the interviewee to remember some items due to shared experiences about medicinal plants with this person previously.
This may also be related to the fact that the interview on medicinal plants does not have questions that are too intimate or sensitive to the interviewee to become embarrassing in the presence of another person. Thus, it is believed that the presence of a third party interferes with the interview only when they are interested in the interviewee’s response [25, 47] and reporting on known medicinal plants within the community is a relatively simple question.
For example, people may feel intimidated in reporting about some plants, especially if they are related to something more intimate, such as diseases related to the genitourinary system (prostate, urinary inflammation, inflammation of the uterus, among others) and this can lead the participant to omit certain plants. However, it is worth mentioning that the question was very general: which medicinal plants do you “know”? Thus, they were able to cite the plants without directly relating to those that are used in their daily lives. This possibly did not interfere with the fact that a person was present during the interview.
In this context, the researcher will be aware of his actions when using this technique in the presence of third parties. The researcher may, depending on the circumstances, decide whether to continue the interview, return at another time and/or simply leave. Thus, the presence of a third party can be beneficial if the objective of the research is to capture the general knowledge of a community.
However, we stress the need for more detailed research, in order to verify in which situation the presence of a third party is positive or negative during the interviews with the use of the free list. For example, checking whether the presence of a person of the opposite sex intimidates the participant from reporting certain types of plants associated with the treatment of any gender-related illness.
Even though it is not the interviewer’s desire, the interviews suffer external influences during the research, which is beyond the control of the researcher . During this work, “potential interview-influencing factors” (Table 2) were also present, although these did not interfere with the plant species mentioned in the free lists.
The low similarity found in the free lists at different times indicates that something made the participants lose their attention during the interview. However, extrinsic factors were not the drivers of such inattention. We therefore, believe that these factors have not interfered free lists similarity precisely because they make the environment as natural as possible for the interviewee. If the interviewees had been placed in an artificial context, that is, in a controlled interview location, it could have been difficult to report the information. This finding is consistent with the literature , which states that for data collection to occur effectively it is necessary that it takes place in the most familiar way to the interviewee.
What else could influence the similarity of free lists?
Considering that extrinsic factors were not able to explain free lists similarity, pehaps intrinsic characteristics of the free lists account for this behavior. Free listing has the reputation of being a simple data collection technique that allows information to be obtained quickly , only requiring short answers, which would decrease the chance of the participant not concentrating on answering them . However, the plant medicinal category is often a large domain. Kujawska et al. , for example, studied rural communities in Misiones (Argentina) and found that the medicinal category presented the highest number of species and properties. Therefore, people trying to list all medicinal plants are essentially juggling several (sub)categories in their minds, which is much more taxing to the mind's executive functioning. For this reason, some researchers have argued that narrowing the domain could make the free lists more complete whereas general domains result in incomplete and scattered lists . The difficulties in sucessfully mentioning items within a large domain can be due to memory issues (as discussed before) and potentialized inatention in contexts of long-lasting interviews. For this reason, in situations when the elders are the most knowleadgeble, their high number of known species can increase the odds for information omission during the free lists. This pattern may also have contributed to the lower free list similarities for the elders.
Were the most cited species the same in the two distinct free list events?
Although some medicinal plants were only mentioned in one of the free list events, different free lists tend to indicate the same species as the most cited. Although free lists focus on individual knowledge, each individual is part of a higher instance (i.e., local knowledge) [52, 53]. Therefore, individual omissions do not seem to bias the free list aggregate outcomes, which is why it is a (well-known) important tool to search for culturally important species.
However, as most ethnobiological studies with free lists focus on the whole set of medicinal products (plants and/or animals), it is possible that interviewees disproportionally forget/omit certain species or subcategories. Flores and Quinlan  investigated medicinal plants used by Dominicans and found that the free lists did not exhibit the gynecological conditions for which they used medicinal plants. For this reason, we need to study the effects of different data collection tools on the aggregate data outcomes as well as the effects of narrowing the domain (e.g., focusing on specific therapeutic indications).