Statistical properties of minimal sufficient balance and minimization as methods for controlling baseline covariate imbalance at the design stage of sequential clinical trials

Common scale minimal sufficient balance: An improved method for covariate-adaptive randomization based on the Wilcoxon-Mann-Whitney odds ratio statistic

Minimal sufficient balance (MSB) is a recently suggested method for adaptively controlling covariate imbalance in randomized controlled trials in a manner which reduces the impact on randomness of allocation over other approaches by only intervening when the imbalance is sufficiently significant. Despite its improvements, the approach is unable to consider the relative clinical importance or magnitude of imbalance in each covariate weight, and ignores any imbalance which is not statistically significant, even when these imbalances may collectively justify intervention. We propose the common scale MSB (CS‐MSB) method which addresses these limitations, and present simulation studies comparing our proposed method to MSB. We demonstrate that CS‐MSB requires less intervention than MSB to achieve the same level of covariate balance, and does not adversely impact either statistical power or Type‐I error.

Impact of minimal sufficient balance, minimization, and stratified permuted blocks on bias and power in the estimation of treatment effect in sequential clinical trials with a binary endpoint

Minimization is among the most common methods for controlling baseline covariate imbalance at the randomization phase of clinical trials. Previous studies have found that minimization does not preserve allocation randomness as well as other methods, such as minimal sufficient balance, making it more vulnerable to allocation predictability and selection bias. Additionally, minimization has been shown in simulation studies to inadequately control serious covariate imbalances when modest biased coin probabilities (≤0.65) are used. This current study extends the investigation of randomization methods to the analysis phase, comparing the impact of treatment allocation methods on power and bias in estimating treatment effects on a binary outcome using logistic regression. Power and bias in the estimation of treatment effect was found to be comparable across complete randomization, minimization, and minimal sufficient balance in unadjusted analyses. Further, minimal sufficient balance was found to have the most modest impact on power and the least bias in covariate-adjusted analyses. The minimal sufficient balance method is recommended for use in clinical trials as an alternative to minimization when covariate-adaptive subject randomization takes place.

Early or delayed parenteral nutrition for infants: what evidence is available?

PURPOSE OF REVIEW

To review the current evidence evaluating early versus delayed commencement of parenteral nutrition in infants.

RECENT FINDINGS

Recent studies in very premature infants (<32 weeks gestation) have shown that early commencement of parenteral nutrition immediately after birth improves physical growth. However, there are concerns that early use of very high dose of amino-acids (>3.5 g/kg/day immediately after birth) may cause metabolic acidosis, elevated blood urea, slower head growth and refeeding-hypophosphatemia syndrome. A recent multicentre randomized controlled trial found that commencement of parenteral nutrition within 24-h of admission increases the risk of infections and prolongs the duration of ventilation and ICU stay in full-term neonates, older infants and children. The study also found that delaying to day 8 of admission increased the risk of hypoglycaemia.

SUMMARY

Benefits of commencing parenteral nutrition on the first day of life appear to outweigh risks in very premature infants; however, it is prudent to avoid early very high doses of amino acids (>3.5 g/kg/day) in the first few days of life. In moderate to late preterm infants, if enteral feeds are not tolerated by 72 h, it is reasonable to commence parenteral nutrition. In full-term and older infants, it is preferable to avoid parenteral nutrition within 24 h of admission and consider delaying by further few days. Diligent monitoring of blood glucose, serum phosphate and other parameters is essential while on parenteral nutrition.