Skip to content

Monthly Archives: March 2018

Type I and Type II Error in Statistics


We often use inferential statistics to make decisions or judgements about the value of a parameter, such as a population mean. For example, we might need to decide whether the mean weight, 𝜇, of all bags of pretzels packaged by a particular company differs from the advertised weight of 454 grams, or we might want […]

Missing or Poor Quality Data in Clinical Trials


In most trials, participants have data missing for a variety of reasons. Perhaps they were not able to keep their scheduled clinic visits or were unable to perform or undergo the particular procedures or assessments. In some cases, follow-up of the participant was not completed as outlined in the protocol. The challenge is how to […]

Systematic Review – Defining the Question


Eligibility Criteria The acronym PICO helps to serve as a reminder of the essential components of review question. One of the features that distinguish a systematic review from a narrative review is the pre-specification of criteria for including and excluding studies in the review (eligibility criteria). Eligibility criteria are  a combination of aspects of the […]

Assumptions for Common Statistic Procedures


Observational Studies and Designed Experiments Besides classifying statistical studies as either descriptive or inferential, we often need to classify them as either observational studies or designed experiments. In an observational study, researchers simply observe characteristics and take measurements, as in a sample survey. In a designed experiment, researchers impose treatments and controls and then observe […]

Chi-Square Goodness-of-Fit Test


The statistical-inference procedures discussed in this thread rely on a distribution called the chi-square distribution. A variable has a chi-square distribution if its distribution has the shape of a special type of right-skewed curve, called a chi-square curve. Actually, there are infinitely many chi-square distributions, and we identify the chi-square distribution in question by its […]