Table 9 Overview of recommendations and considerations for use of the various subtypes

Subtype A1: Longitudinal data approach

Suitable when the phenomenon of interest is expected to vary over time. Change is not the focus of the study

• Aspects of time/change are not analyzed

• This subtype is not in line with existing definitions of QLR and should rather be identified as QLD

Subtype A2: Partial longitudinal approach

Suitable when the phenomenon of interest is the major focus and change over time is secondary

• A borderline case regarding QLR methodological recommendations

• The studies present longitudinal data and results, but time/change plays a minor role and is often presented last

• Risk of results becoming fragmentized when time/change is presented separately from the phenomenon

• Risk that aspects of time/change are superficially described because of limited space when several research questions are presented in the results section

Subtype B1: Recurrent cross-sectional approach

Suitable when the focus is to describe experiences/a phenomenon across time and

• A borderline case in relation to QLR method recommendations

1) Participants are expected to undergo similar experiences at the same pace, for example, a health-care pathway, an intervention, or an education program

• Longitudinal data collection is used, and findings consist of experiences over time. However, the diachronic (through time) perspective is often weak or lacking

2) When different aspects of the phenomenon are in focus at different time points of data collection, for example, incitements and maintenance are addressed at two different time points during data collection

• Studies interviewing different groups of participants before and after could potentially yield similar results

• The contrast between time points is important

• Crucial to follow the same data collection plan for all participants

• There should not be too many data collection periods or data collection periods too close in time, which could lead to ambiguous result presentations

• The time points should have a logical rationale connected to the phenomenon of interest

• It is recommended that comparisons be made between time points as a synthesized part of the results to incorporate some aspects of change

• Can be combined with mixed methods if quantitative data are collected at the same time points as qualitative data

Subtype B2: Sequence of events approach

Suitable in projects in which the goal is to describe experiences/a phenomenon across time, especially if the phenomenon has a defined beginning and unfolds at a similar pace across participants

• The element of time is evident; change is less in focus

• The focus on time over change might depend upon these studies’ predominantly descriptive character

• The timeline in this subtype is logically constructed by the researcher; therefore, some participants might not add to all parts of the results

• Not dependent on distinct time points for data collection; instead, participant-adapted data collection (where the amount of data and the tempo of data collection can vary across participants) might be advantageous

• During longitudinal data collection, participants can provide different information regarding the same event since memories are reconstructed over time. In Subtype B2, the results unfold chronologically, and thus, researchers must consider how to manage reconstruction of memories in the analysis and results

Subtype C1: Longitudinal themes approach

Suitable when the intention is to describe change through time in complex and multidimensional phenomena

• A possible challenge is displaying how the different themes coexist and interact across time. In some studies, this is shown in a conceptual model or by a few illustrative cases

• Themes can be inductively constructed or predefined, depending upon how much is known about the phenomenon

• A risk might be that some themes are less thoroughly followed across the data collection, resulting in difficulties analyzing changes in themes across time

• Predefined themes can provide the advantage of themes well integrated into interview guides and data collection strategies; inductive themes can be more accommodative of the data

• Can be combined with mixed methods if quantitative variables can mirror the qualitative themes

Subtype C2: Longitudinal case approach

Suitable for projects in which cases are expected to have various trajectories or when contextual factors are likely to render large variations within the sample

• It is important to collect data to obtain a deep understanding of each participant/case; otherwise, there is a risk that some trajectories will be superficially described. Therefore, this subtype is sensitive to dropouts and probably needs more data from each participant/case than subtypes describing data on a group level

• Can also be relevant if the aim is to unpack change on a more detailed level, for example, how an intervention worked for some participants but not for others

• Using a participant-adapted data collection strategy and/or several data collection points is probably advantageous. The data collection should be crafted around the periods of most change in participants/cases

• Could be combined with mixed methods if quantitative data can be divided by subgroups/trajectories

Subtype C3: Longitudinal process approach

Suitable when researchers want to create qualitative explanations for change, for example, developing models and understanding what makes change happen

• Time is of lesser interest, since change processes are not necessarily chronological

• Probably the most time-consuming and complex subtype to conduct

• Using a participant-adapted data collection strategy and/or several data collection points is probably advantageous in order to collect nuanced data on change when most changes are happening

• It is probably advantageous to collect several types of data and/or add elements of theoretical sampling; such strategies may support a fuller description of the process

• Requires an interpretive and complex analysis