Guidelines for determining nonprobabilistic sample sizes are virtually nonexistent. Purposive samples are the most commonly used form of nonprobabilistic sampling, and their size typically relies on the concept of “saturation,” or the point at which no new information or themes are observed in the data. Although the idea of saturation is helpful at the conceptual level, it provides little practical guidance for estimating sample sizes, prior to data collection, necessary for conducting quality research. Using data from a study involving sixty in-depth interviews with women in two West African countries, the authors systematically document the degree of data saturation and variability over the course of thematic analysis. They operationalize saturation and make evidence-based recommendations regarding nonprobabilistic sample sizes for interviews. Based on the data set, they found that saturation occurred within the first twelve interviews, although basic elements for metathemes were present as early as six...

https://www.rincondepaco.com.mx/rincon/Inicio/Seminario/Documentos/Met_otros/Docs_Dra_Fleiz/Lecturas_sugeridas/Guest_data_saturation_interviews.pdf

How Many Interviews Are Enough?: An Experiment with Data Saturation and Variability

Purposeful sampling is widely used in qualitative research for the identification and selection of information-rich cases related to the phenomenon of interest. Although there are several different purposeful sampling strategies, criterion sampling appears to be used most commonly in implementation research. However, combining sampling strategies may be more appropriate to the aims of implementation research and more consistent with recent developments in quantitative methods. This paper reviews the principles and practice of purposeful sampling in implementation research, summarizes types and categories of purposeful sampling strategies and provides a set of recommendations for use of single strategy or multistage strategy designs, particularly for state implementation research.

/pdf/purposeful-sampling-for-qualitative-data-collection-and-2zi83jnr1f.pdf

Purposeful Sampling for Qualitative Data Collection and Analysis in Mixed Method Implementation Research.

Saturation has attained widespread acceptance as a methodological principle in qualitative research. It is commonly taken to indicate that, on the basis of the data that have been collected or analysed hitherto, further data collection and/or analysis are unnecessary. However, there appears to be uncertainty as to how saturation should be conceptualized, and inconsistencies in its use. In this paper, we look to clarify the nature, purposes and uses of saturation, and in doing so add to theoretical debate on the role of saturation across different methodologies. We identify four distinct approaches to saturation, which differ in terms of the extent to which an inductive or a deductive logic is adopted, and the relative emphasis on data collection, data analysis, and theorizing. We explore the purposes saturation might serve in relation to these different approaches, and the implications for how and when saturation will be sought. In examining these issues, we highlight the uncertain logic underlying saturation—as essentially a predictive statement about the unobserved based on the observed, a judgement that, we argue, results in equivocation, and may in part explain the confusion surrounding its use. We conclude that saturation should be operationalized in a way that is consistent with the research question(s), and the theoretical position and analytic framework adopted, but also that there should be some limit to its scope, so as not to risk saturation losing its coherence and potency if its conceptualization and uses are stretched too widely.

https://link.springer.com/content/pdf/10.1007%2Fs11135-017-0574-8.pdf

Saturation in qualitative research: exploring its conceptualization and operationalization

Sample sizes must be ascertained in qualitative studies like in quantitative studies but not by the same means. The prevailing concept for sample size in qualitative studies is "saturation." Saturation is closely tied to a specific methodology, and the term is inconsistently applied. We propose the concept "information power" to guide adequate sample size for qualitative studies. Information power indicates that the more information the sample holds, relevant for the actual study, the lower amount of participants is needed. We suggest that the size of a sample with sufficient information power depends on (a) the aim of the study, (b) sample specificity, (c) use of established theory, (d) quality of dialogue, and (e) analysis strategy. We present a model where these elements of information and their relevant dimensions are related to information power. Application of this model in the planning and during data collection of a qualitative study is discussed.

Sample Size in Qualitative Interview Studies: Guided by Information Power

萨义德以其独特的双重身份,对西方中心权力话语做了分析,通过对文学作品、演讲演说等文本的解读,将O rie n ta lis m——"东方学",做了三重释义:一门学科、一种思维方式和一种权力话语系统,对东方学权力话语做了系统的批判,同时将东方学放入空间维度对东方学文本做了细致的解读。

萨义德的“Orientalism”释义

The objective of this study was to highlight the value of preventing unintended pregnancies among HIV-infected women as a strategy to prevent perinatal HIV transmission. Goal: The goal of this study was to assess the cost-effectiveness of family planning programs to avert HIV-positive births with the current programmatic emphasis: prenatal care services that provide and promote nevirapine for prevention of mother-to-child transmission of HIV. Cost-effectiveness analyses were conducted from the health system perspective during 1 year with a hypothetical sub-Saharan African population. Expected program costs were combined with number of HIV-positive births averted for each strategy. Results: At the same level of expenditure the contraceptive strategy averts 28.6% more HIV-positive births than nevirapine for prevention of mother-to-child transmission of HIV. Increasing contraceptive use among nonusers of contraception who do not want to get pregnant is cost-effective and is an equally important strategy to prevent perinatal transmission as prenatal care programs that provide and promote nevirapine to HIV infected mothers. (authors)

The value of contraception to prevent perinatal HIV transmission.

BACKGROUND: One of the concerns raised regarding the introduction of any new HIV-prevention measure such as PrEP is the potential for risk disinhibition or sexual risk compensation. The oral tenofovir HIV prevention trial has been the subject of international discussion in this regard. METHODS: This article maps the changes in sexual risk behavior among women participating in the oral tenofovir HIV prevention trial in Ghana. Content-driven thematic analysis was carried out on qualitative data obtained from in-depth interviews with study participants. Growth curve analysis was the primary method used to document trends over time in self-reported sexual behavior collected monthly. RESULTS: Overall the study found that sexual risk behavior did not increase during the trial. Number of sexual partners and rate of unprotected sex acts decreased across the 12-month period of study enrollment. Certain subgroups of women however exhibited different growth curves. Data indicate that the HIV prevention counseling associated with the trial was effective. CONCLUSIONS: Counseling during the trial was effective. Different types of counseling and messaging may be needed for different subgroups within a population. These findings also have implications for required sample sizes for future HIV prevention trials where seroconversion is the main outcome.

Changes in sexual risk behavior among participants in a PrEP HIV prevention trial.

Background Self-reports are widely used for measuring behaviour in HIV research and prevention, yet the accuracy of these measures has been shown to be questionable in many cases. Social desirability bias (SDB) is one of the key factors identified as affecting self-report accuracy. Methods Using in-depth interviews, we examined SDB from the perspective of 60 women at high risk for HIV in two West African countries: Ghana and Nigeria. We solicited suggestions for reducing SDB in the context of HIV research and prevention, and asked for feedback regarding methods currently being employed to reduce SDB. Results Themes pertaining to fear and a desire to have a better life were pervasive throughout the data. Thematic structure was similar between sites and age groups, although younger women tended to be more concerned about the interview context. Conclusions Vulnerability of a population should be considered when asking sensitive questions. Audio-computer-assisted self-interviews may not be appropriate for vulnerable populations in developing countries, particularly for older respondents.

https://srh.bmj.com/content/familyplanning/31/4/285.full.pdf

Fear, hope and social desirability bias among women at high risk for HIV in West Africa.

Objective: To assess the acceptability of a daily pill for prevention of HIV acquisition among 400 Ghanaian women in the oral tenofovir disoproxil fumarate (TDF) clinical trial. Methods: Structured questionnaires were conducted with women enrolled in the trial at enrollment and at each of the 12 monthly follow-up visits. Growth curve analysis was used to examine adherence patterns over time. Qualitative interviews were carried out with a subsample of the clinical trial population, and thematic analysis was applied to these data. Results: Overall, acceptability of the pill was good. Adherence remained > 82% throughout the 12-month trial. Consistent access to the pill and study assignment were both associated with adherence. Most reported problems diminished over time as women became accustomed to the pill and developed strategies to incorporate pill taking into their daily routines. Conclusions: If daily preexposure prophylaxis (PrEP) for HIV is found to be efficacious and has as few physical side...

Laura Johnson

Papers

How Many Interviews Are Enough?: An Experiment with Data Saturation and Variability

The value of contraception to prevent perinatal HIV transmission.

Changes in sexual risk behavior among participants in a PrEP HIV prevention trial.

Fear, hope and social desirability bias among women at high risk for HIV in West Africa.

Acceptability of PrEP for HIV prevention among women at high risk for HIV.