outcome of a coin flip for example crossword

In the bottom panel, stratified sampling was used: cases were first grouped into strata, then simple random sampling was employed to randomly select 3 cases within each stratum. In the top panel, simple random sampling was used to randomly select the 18 cases (denoted in red).

The act of taking a simple random sample helps minimize bias.Įven when people are picked at random, e.g., for surveys, caution must be exercised if the non-response rate is high.įor instance, if only 30% of the people randomly sampled for a survey actually respond, then it is unclear whether the results are representative of the entire population.įigure 2.5: Examples of simple random and stratified sampling. This means that each case in the population has an equal chance of being included and the cases in the sample are not related to each other. The most basic random sample is called a simple random sample and is equivalent to drawing names out of a hat to select cases. Sampling randomly helps address this problem. If someone was permitted to pick and choose exactly which graduates were included in the sample, it is entirely possible that the sample would overrepresent that person’s interests, which may be entirely unintentional. The terms statistic and parameter are useful for communicating claims and models and will be used extensively in later chapters which delve into making inference on populations.įigure 2.3: Asked to pick a sample of graduates, a nutrition major might inadvertently pick a disproportionate number of graduates from health-related majors. We use specific terms in order to differentiate when a number is being calculated on a sample of data ( statistic) and when it is being calculated or considered for calculation on the entire population ( parameter). Yet, we can still conceptualize calculating the average income of all adults in Argentina. So, a “typical” numerical summary is calculated from a sample. However, measuring every unit in the population is usually prohibitive (so the parameter is very rarely calculated). The number (or set of numbers) may be a quantity you are already familiar with (like the average) or it may be something you learn through this text (like the slope and intercept from a least squares model, provided in Section 7.2).Ī numerical summary can be calculated on either the sample of observation or the entire population. In most statistical analysis procedures, the research question at hand boils down to understanding a numerical summary. Ideally, a sample is a small fraction of the population.įor instance, 60 swordfish (or some other number) in the population might be selected, and this sample data may be used to provide an estimate of the population average and to answer the research question. Oftentimes, it is not feasible to collect data for every case in a population.Ĭollecting data for an entire population is called a census.Ī census is difficult because it is too expensive to collect data for the entire population, but it might also be because it is difficult or impossible to identify the entire population of interest! In the first question, the target population is all swordfish in the Atlantic Ocean, and each fish represents a case. Does a new drug reduce the number of deaths in patients with severe heart disease?Įach research question refers to a target population.Over the last five years, what is the average time to complete a degree for Duke undergrads?.What is the average mercury content in swordfish in the Atlantic Ocean?.25 Inference for linear regression with multiple predictorsĬonsider the following three research questions:.

24 Inference for linear regression with a single predictor.21 Inference for comparing paired means.20 Inference for comparing two independent means.17 Inference for comparing two proportions.12 Confidence intervals with bootstrapping.11 Hypothesis testing with randomization.8 Linear regression with multiple predictors.7 Linear regression with a single predictor.

Outcome of a coin flip for example crossword