Using Model-Based Clustering to Improve Qualitative Inquiry: Computer-Aided Qualitative Data Analysis,Latent Class Analysis,and Interpretive Transparency

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - A combination of computer-aided qualitative data analysis (CAQDAS) and latent class analysis (LCA) can substantially...     

Insignificant Betas and the Efficacy of the Sharpe Diagonal Model for Portfolio Selection*

When both practitioners and theorists apply Sharpe's diagonal model [15] to simplify the portfolio selection problem, they assume that the entire covariation structure of each stock (i.e., with all other stocks) is captured in that stock's covariance with the market (or β). Furthermore, it is well known that the selection algorithm itself has a marked tendency to select stocks with the lowest βs, ceteris paribus. When a stock's β is statistically indistinguishable from zero, it is an empirical issue whether the market model is (a) less appropriate for that particular stock relative to those with statistically significant βs; or is (b) a viable model in that the covariance of this stock's rate-of-return with all other stocks' rates-of-return vanishes. The objective of this paper is to distinguish empirically between (a) and (b), and to propose a heuristic which will improve the ex-post performance of the diagonal model. The possible benefits of this heuristic are also demonstrated in a rigorous statistical framework.     

Estimating dual headed time in food production with implications for SNAP benefit adequacy

Intrahousehold resource allocations have important implications for policies targeted at household resources and thus household welfare. Recent literature has shown, for single headed households, that the Supplemental Nutrition Assistance Program benefits may be inadequate to reach a nutritious diet due to a “time deficit” gap in food production. This paper first develops a simple theoretically based time adjustment multiplier to address this benefit inadequacy for single and dual headed households. A method is then developed for estimating spousal time in food production with limited data. The estimated time deficit gap and time adjustment multiplier are smaller for dual headed households than single headed households. For single headed households, the time adjusted benefits are about $107 per household per week higher than the unadjusted benefits. For dual headed households, ignoring the spousal time contribution, the time adjusted benefits are about $73 per household per week higher than the unadjusted benefits. However, by including the spousal time contribution, this benefit shortfall is reduced by about $50. These findings demonstrate the importance of taking into account intrahousehold time allocation in evaluating the adequacy of the Supplemental Nutrition Assistance Program benefits.

     

Impact of child health and disability on subsequent maternal fertility

The prevalence of chronic conditions among children has been rising in the past four decades. Despite the policy relevance and plausible mechanisms through which child disability and severe early life health conditions can impact subsequent maternal reproductive behavior, there has been limited investigation of this question particularly in the US. Child disability or severe early life health problems such as very preterm birth (VPTB) and very low birth weight (VLBW) can constrain household resources to have another child but may also increase parental demand for healthy children and modify allocation of resources between children. Empirical assessment of this question is complicated by unobservables such as maternal health and preferences. We examine whether giving birth to a child with disabilities or severe adverse birth outcomes including VPTB and VLBW impacts subsequent maternal fertility. We employ a mother fixed-effect duration model for maternal fertility over time as a function of the proportion of previously born children with disabilities/health conditions in order to account for time-invariant unobservables, using merged data from the 1993 National Health Interview Survey and 1995 National Survey of Family Growth. We find no evidence that having disabled children reduces subsequent live births when using the mother fixed-effect model, in contrast to the classical model using within and between mother variation which suggests a fertility decline. Similarly, we find no evidence that having VPTB or VLBW children reduces fertility. Overall, our findings indicate no impact of child disability or health conditions on subsequent maternal fertility. Additional analyses excluding women who may qualify for AFDC show overall a similar pattern of results, suggesting that the findings may be generalizable post the AFDC. Time-varying unobservables may still be at work, but they likely result in an opposite (negative) bias toward reduction in fertility.