Independent unpaired samples[ edit ] The independent samples t-test is used when two separate sets of independent and identically distributed samples are obtained, one from each of the two populations being compared.

With low birth rates and death rates, the population only grows slowly, if at all.

The simulated random numbers originate from a bivariate normal distribution with a variance of 1. While the world's average fertility rate is about 3 children per woman, its fecundity rate is about 20 per woman.

Most poor countries today fit into this stage. Given this trend, the global population will exceed 6 billion in the early s, and 8 billion by the s. Stage 3 suggests that technology holds the key to population control.

Each of these statistics can be used to carry out either a one-tailed or two-tailed test. Elizabeth Pearman Copyright You now have a research problem and have probably asked a question but in order to ask a really good question, you need to be able to identify the population you want to use in the study.

Elementary school students is a pretty big group so perhaps we decide to use only third grade students or some other grade. For example, women over age 40 or under age 19 have an increased risk of bearing a child of low birth weight, and thus a variety of birth defects and even outright death.

Most two-sample t-tests are robust to all but large deviations from the assumptions. When we conduct a study that looks at only one variable, we say that we are working with univariate data.

As noted by the New Malthusians, a group of demographers, assets such as habitable and fertile land, clean air, and fresh water are finite resources. In this case, we have two independent samples and would use the unpaired form of the t-test.

If the calculated p-value is below the threshold chosen for statistical significance usually the 0. Most societies throughout history have stayed at this stage.

Infant mortality rate, which is the number of deaths among infants under age one for each 1, live births in a year, provides demographers with another measure. Social Movements Population and Demographic Variables Humans throughout history have generally favored large families—for the most part to assure survival of a particular family line or racial group.

If a variable can take on any value between its minimum value and its maximum value, it is called a continuous variable; otherwise, it is called a discrete variable.

Estimates say that approximately one million teenage women in the United States become pregnant each year. Similar to the crude birth rate, demographers calculate the crude death rate, or the number of deaths annually per 1, people in the population.

And with medical advances increasing fertility and lowering death rates, the global population continues to grow exponentially with no end in sight.

The highest fertility rate nearly 6 children per woman in the world occurs in Africa, whereas the lowest occurs in Europe about 1. A variable is an attribute that describes a person, place, thing, or idea. One thing to think of in identifying the population is to keep in mind where you might find this population and how will you have access to them.

Your browser does not support HTML5 video. A typical example of the repeated measures t-test would be where subjects are tested prior to a treatment, say for high blood pressure, and the same subjects are tested again after treatment with a blood-pressure lowering medication. Each of these statistics can be used to carry out either a one-tailed or two-tailed test.

The sex ratio in the United States is about 93 males for every females. Two-sample t-tests for a difference in mean involve independent samples unpaired samples or paired samples. In this stage, birth and death rates roughly balance each other.

Demographers determine a population's natural growth rate by subtracting the crude death rate from the crude birth rate. Population composition Demographers also take an interest in the composition of a society's population.

And with medical advances increasing fertility and lowering death rates, the global population continues to grow exponentially with no end in sight. Paired t-tests are a form of blockingand have greater power than unpaired tests when the paired units are similar with respect to "noise factors" that are independent of membership in the two groups being compared.

He also warned that food production would only increase arithmetically 1, 2, 3, 4, 5 … because of limitations in available farmland. You might want to put some specificity to identifying your potential population by being more specific so rather than Mothers or boys and girls you might specify an age group, or a typology, or a diagnosis.Population and Demographic Variables Humans throughout history have generally favored large families—for the most part to assure survival of a particular family line or racial group.

High death rates from plagues, predators, and wars led people to produce as many offspring as possible. A paired samples t-test based on a "matched-pairs sample" results from an unpaired sample that is subsequently used to form a paired sample, by using additional variables that were measured along with the variable of interest.

Population, Sample and Variables zPopulation: all the subjects of interest zSample: subset of the population - data is collected on the sample zResponse variable: measures the outcome of interest zExplanatory variable: the variable that explains the response variable.

Agresti/Franklin Statistics, 2of. Mortality, or the number of deaths in a society's population, also influences population size. Similar to the crude birth rate, demographers calculate the crude death rate, or the number of deaths annually per 1, people in the population.

Variables: A population variable is a descriptive number or label associated with each member of a population. The values of a population variable are the various numbers (or labels) that occur as we consider all the members of the population.

Values of variables that have been recorded for a population or a sample from a population constitute data. Identify the population, variable of interest, and type of variable in the following: 1.

The dean of the College of Arts and Sciences would like to determine the average weekly allowance of .

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