Methods and Issues in Life Span Development

1. Methods and Issues in Life Span Development

2. The Old Debate: Nature vs Nurture Development is both influenced by “nature”, more commonly called heredity when speaking of life span development, and “nurture”, often called environment. The “old debate” is no longer really an issue of “either/or” in contemporary psychology: researchers understand that while each individual inherits a specific pattern of genes from their parents, the expression of those genes is influenced by the environment in which they grow. Today, the debate is more to what degree each affect development. Examples: Different stressors a woman experiences while pregnant can influence the genetic makeup of her fetus. An individual with a genetic risk for Alzheimer’s may not be afflicted if they’ve remain physically and mentally active.

3. Continuity and Change in Development To make talking about life span development easier, we speak of stages of from infancy through old age, but in reality, people develop in a contiguous fashion throughout life. Even periods marked by specific biological changes, like puberty and climacteric (called “menopause” in women) occur gradually. The issue of stability vs change in development now mostly refers to whether people’s personalities change as they age. Does the difficult and whiny child turn into a nervous and worrying adult? In early 20th century psychology, psychologists such as William James believed that personality was set in stone by the age of 30. Today, most psychologists agree that personalities influence our life choices, which can then influence our personalities.

5. Critical Periods In early human development, certain factors must be present at specific ages for growth to occur normally. These can be biological: growth of the nervous system is a vital part of human development, but can negatively affected by maternal sickness early in pregnancy. This can also include the development of sensory abilities, such as depth perception in early infancy. In general, critical periods become less relevant as we age. In later stages, plasticity shows more importance in humans, as they often show an ability to recover from mental trauma, such as regaining language facilities after cerebral hemorrhaging. The term critical period means that something has to happen within a certain time frame to develop normally, like animals imprinting on their mothers.

6. Basic Developmental Terms When discussing life span development, some key terms pop up quite often. Here they are with working definitions: Life Span: The biological limits to life’s length, determined by species-specific hereditary factors Life Expectancy: The average length of time that a given age-based organism is expected to live. (Note: This is usually measured from birth to death. In recent years, human life span has not increased, but life expectancy has.) Life Course: The term used by sociologists to refer to the normal, expected set of events that take place over an individual’s life, determined in many ways by society’s norms.

7. Research Methods in Life Span Development Studies to investigate life span development usually fall into two categories: descriptive and sequential. Those will be discussed more in detail shortly. All research into life span development is, by its nature, quasi-experimental. It is impossible to make a truly unbiased and rigorous life span experiment. The experiment cannot be true is age or gender as assigned as independent variables, as these cannot be randomly assigned (you cannot modify a participant’s age or gender). However, you can test to see if certain conditions have varying impacts on different age groups.

8. Age as Bias Another problem with research on aging is that as samples grow older, they become less representative of the population. Adults who live to their 80s and beyond are a select group who have gotten lucky with a combination of genes and lifestyle choices. Even those who are only 25-30 years old may demonstrate this bias, as there is a relatively large number of accidental deaths before the age of 25. In other words, people who take large risks, be that skydiving or drunk driving, are less likely to live past 25, as impulses for risky behavior decrease with age. Similarly, you only get people of advanced age in trials who are healthy, as those who are not are either too sick to participate, or are dead.

9. Main Concepts Underlying Research in Development Age: The chronological age of an individual Cohort: The historical period in which the individual was born Time of Measurement: The historical period in which testing takes place Because any one of these numbers are determined when the other two are known, researchers can’t know if a particular pattern of findings is due to the age of the participant or due to the historical period (of birth or of testing).

10. Descriptive Research Designs Three types of studies are considered “descriptive” because they do not attempt to separate personal from social aging. Cross-sectional: Individuals from different cohorts are compared at one point in time. Longitudinal: Individuals from one cohort are followed over several time periods. Time Lag: Individuals of the same age who were born at different times and are being tested in the same year are compared. An example of this would be comparing a high school class of athletes from 2009 with a high school class of athletes in 1959. Holding age constant points out generational differences.

11. Sequential Research Designs Time-Sequential Design: A longitudinal study is replicated for more than one cohort. It repeats a study for different subjects born at different times. For instance, a group of researchers may follow some children from ages 5-12 and see how they develop academically. They then repeat this for other groups of children born later, the same 5-12 range. By repeating the experiment, they don’t make any errors based on a single sample.

12. Twin Studies Once, twin studies were cherished by psychology as potentially “proving” the nature-nurture debate. However, they are now being questioned on several grounds. Only a small minority of monozygotic twins (1%) are truly and fully identical. About 20-25% are dichorionic diamniotic (two placentas, two amniotic sacs), and the rest are monochorionic diamniotic (one placenta, two amniotic sacs). This means that twins who may seem identical actually had different prenatal environments, which can have an impact throughout life.

13. Twins, continued The most common twin study compares identical (monozygotic) and same-sex fraternal (dizygotic) twins. The idea being that the environment should be the same, so only the genetic similarities should make differences. However this has been criticized because the assumption that pairs of fraternal twins will be treated the same has been proven false. (In several cases, parents may treat one fraternal twin differently than the other for a variety of reasons)

14. Previous studies of twins reared apart exaggerated similarities and ignored differences. Many documentaries on the topic always report on the hits, but not the differences. These studies might be rightfully criticized because the of the degree to which identical twins split at birth experience very different environments and lives.