THE t TEST: An Introduction

The t distribution is a probability distribution similar to the Normal distribution. It is commonly used to test hypotheses involving numerical data. This paper provides an understanding of the t distribution and uses a musculo-skeletal example to illustrate its application

AN INTRODUCTION TO PROBABILITY DISTRIBUTIONS

Probability allows us to infer from a sample to a population. In fact, inference is a tool of probability theory. This paper looks briefly at the Binomial, Poisson, and Normal distributions. These are probability distributions, which are used extensively in inference. An understanding of these distributions will assist the chiropractor and osteopath to critically appraise the literature

Placental Insufficiency in Fetuses That Slow in Growth but Are Born Appropriate for Gestational Age: A Prospective Longitudinal Study.

OBJECTIVES:To determine whether fetuses that slow in growth but are then born appropriate for gestational age (AGA, birthweight >10th centile) demonstrate ultrasound and clinical evidence of placental insufficiency. METHODS:Prospective longitudinal study of 48 pregnancies reaching term and a birthweight >10th centile. We estimated fetal weight by ultrasound at 28 and 36 weeks, and recorded birthweight to determine the relative change in customised weight across two timepoints: 28-36 weeks and 28 weeks-birth. The relative change in weight centiles were correlated with fetoplacental Doppler findings performed at 36 weeks. We also examined whether a decline in growth trajectory in fetuses born AGA was associated with operative deliveries performed for suspected intrapartum compromise. RESULTS:The middle cerebral artery pulsatility index (MCA-PI) showed a linear association with fetal growth trajectory. Lower MCA-PI readings (reflecting greater diversion of blood supply to the brain) were significantly associated with a decline in fetal growth, both between 28-36 weeks (p = 0.02), and 28 weeks-birth (p = 0.0002). The MCA-PI at 36 weeks was significantly higher among those with a relative weight centile fall 30% (mean MCA-PI 1.94 vs 1.56; p<0.01). Of 43 who labored, operative delivery for suspected intrapartum fetal compromise was required in 12 cases; 9/18 (50%) cases where growth slowed, and 3/25 (12%) where growth trajectory was maintained (p = 0.01). CONCLUSIONS:Slowing in growth across the third trimester among fetuses subsequently born AGA was associated with ultrasound and clinical features of placental insufficiency. Such fetuses may represent an under-recognised cohort at increased risk of stillbirth

Novel male hormonal contraceptive combinations: the hormonal and spermatogenic effects of testosterone and levonorgestrel combined with a 5alpha-reductase inhibitor or gonadotropin-releasing hormone antagonist

We postulated that the addition of a combined types I and II, 5alpha-reductase inhibitor (dutasteride) or long-acting GnRH antagonist (acyline) to combination testosterone plus levonorgestrel treatment may be advantageous in the suppression of spermatogenesis for male contraception. This study aimed to examine effects of novel combination contraceptive regimens on serum gonadotropins and androgens and sperm concentration.This study was divided into three phases: screening (2 wk), treatment (8 wk), and recovery (4 wk). Twenty-two men (n = 5-6/group) received 8 wk of treatment with testosterone enanthate (TE, 100 mg im weekly) combined with one of the following: 1) levonorgestrel (LNG) 125 mug orally daily; 2) LNG 125 microg plus dutasteride 0.5 mg orally daily; 3) acyline 300 microg/kg sc every 2 wk (as a comparator for any additional progestin effects); or 4) LNG 125 microg orally daily plus acyline 300 microg/kg sc every 2 wk.Serum gonadotropin levels were similarly suppressed by all treatments, falling to a nadir between 1.2 and 3.4% and 0.5 and 0.8% baseline for FSH and LH, respectively (P < 0.05). Serum dihydrotestosterone levels were significantly (P < 0.05) decreased in the dutasteride group throughout the treatment period to a nadir of 31% baseline (wk 7). No significant differences in sperm concentrations among treatment groups were seen. Severe oligospermia (0.1-3 million/ml) or azoospermia was seen in none of five and four of five in TE + LNG; two of six and four of six in TE + LNG + dutasteride; two of six and four of six in TE + acyline; and one of five and three of five in TE + LNG + acyline groups, respectively. There was one nonresponder in each of the TE + LNG and TE + LNG + acyline groups.We conclude that the addition of a combined types I and II, 5alpha-reductase inhibitor or long-acting GnRH antagonist to a testosterone plus LNG regimen provides no additional suppression of gonadotropins or sperm concentration over an 8-wk treatment period. However, further evaluation of the effects of these regimens on the testis (including testicular steroid levels and germ cell maturation) and the treatment of larger numbers of men (and for longer periods) may provide data to support their place in contraceptive development

Health burden of hip and other fractures in Australia beyond 2000

Objective: To calculate the expected increase in the number of fractures in adults attributable to the predicted increase in the number of elderly Australians.Data sources: All fractures in adult residents (&gt; 35 years) of the Barwon Statistical Division (total population, 218 000) were identified from radiological reports from February 1994 to February 1996. The Australian Bureau of Statistics supplied predictions of Australia\u27s population (1996 to 2051). Main outcome measure: The projected annual number of fractures in Australian adults up to 2051 (based on stable rates of fracture in each age group).Results: The number of fractures per year is projected to increase 25% from 1996 to 2006 (from 83 000 fractures to 104 000). Hip fractures are projected to increase 36% (from 15 000 to 21 000) because of a substantial rise in the number of elderly aged 85 years and over. Hip fractures are expected to double by 2026 and increase fourfold by 2051.Conclusions: In contrast to Europe and North America, where numbers of hip fractures are expected to double by 2026 and then stabilise, in Australia hip fractures will continue to place a growing demand on healthcare resources for many decades. These projections can be used for setting goals and evaluating the costs and benefits of interventions in Australia.<br /

Doppler assessments performed at 36 weeks according to change in weight centile.

<p>MCA-PI according to weight centile change between the ultrasound performed at 28 weeks and 36 weeks (2a) MCA-PI according to weight centile change between the ultrasound performed at 28 weeks and birth (2b). CPR according to weight centile change between the ultrasound performed at 28 weeks and 36 weeks (2c) CPR according to weight centile change between the ultrasound performed at 28 weeks and birth (2d); UA-PI according to weight centile change between the ultrasound performed at 28 weeks and 36 weeks (2e) UA-PI according to weight centile change between the ultrasound performed at 28 weeks and birth (2f). * 5^th, 50^th and 95^th centile for Middle Cerebral Artery Pulsatility Index and Cerebroplacental Ratio at 36 weeks gestation (12); ** 5^th, 50^th and 95^th centile for Umbilical Artery Pulsatility Index at 36 weeks gestation (13).</p

Receiver-operating curves for the outcome of operative delivery (emergency CS or operative vaginal delivery) for suspected fetal compromise among those who underwent labour (n = 12/43) using customised birthweight centile (Fig 4a), change in fetal weight centile between 28–36 weeks (Fig 4b) and change in fetal weight centile between 28 weeks-birth (Fig 4c).

<p>Receiver-operating curves for the outcome of operative delivery (emergency CS or operative vaginal delivery) for suspected fetal compromise among those who underwent labour (n = 12/43) using customised birthweight centile (Fig 4a), change in fetal weight centile between 28–36 weeks (Fig 4b) and change in fetal weight centile between 28 weeks-birth (Fig 4c).</p