Experimental Methods

Question 1

What are the two categories into which studies can be divided based on the role of the researcher or experimenter?

Answer 1

1. Experimental studies
2. Observational studies

As their names indicate, experimental studies involve the researcher manipulating some condition(s) experienced by the groups, while in observational studies, the researcher simply observes and/or measures the sample without interfering.

Question 2

Do randomized controlled trials (RCTs) exemplify observational or experimental studies?

Answer 2

experimental studies

Both the word “randomized” and the word “trial” are hints to the nature of an RCT. “Randomized” indicates that subjects are randomly assigned to different groups, which occurs only in experimental studies. “Trial,” too, has a connotation of experimenting rather than observing.

Question 3

How large, at minimum, must a sample size be for a study to be valid?

Answer 3

There is no minimum sample size, although the larger the sample, the better.

This is important! In studies of extremely rare conditions, for example, it’s not possible to utilize a very large sample, and that’s okay. Be wary of MCAT answer choices that indicate that a study is flawed simply because it has a small sample size, unless the passage/question gives additional information to support this.

Question 4

What is the key limitation of observational studies compared to experimental studies in terms of what they cannot prove?

Answer 4

causation

Since observational studies involve only observation, these studies are highly subject to confounding variables. Additionally, even the direction of causation is often unclear in such a study. For these reasons, only experimental studies can determine causation.

Question 5

Name the type of observational study in which a sample is followed and measured over time.

Answer 5

longitudinal study

Longitudinal studies are advantageous in that they allow researchers to determine the sequence of events that subjects experience. Subjects are often followed for months or years.

Question 6

Name the type of observational study in which samples are evaluated once, at a single point in time, and compared.

Answer 6

cross-sectional study

These studies are highly useful in comparing variables (often, many variables) at a time, but they cannot be easily used to determine sequences of events over time.

Question 7

Fill in the blank.

A classic distinction in research is between ________ and ________.

This distinction refers to whether a change in one variable directly leads to a change in another, or when both changes simply happen to be more likely to occur together.

Answer 7

correlation, causation

Causation, the stronger of the two relationships, occurs when a change in one variable causes a change in another variable.

Correlation occurs when a change in one variable (say, increased blood glucose) simply happens to occur with, but is not necessarily caused by, a change in another variable.

Question 8

Name the value that serves as a statistical measure of the strength of the correlation between two variables.

Answer 8

correlation coefficient

This value ranges from −1.0 to 1.0.

Question 9

True or false.

A negative correlation means that two variables are not associated with each other at all.

Answer 9

False

This is incorrect! A negative correlation means that two variables are associated with each other; specifically, as one variable increases, the other decreases.

In contrast, a positive correlation means that as one variable increases, the other also increases.

Question 10

A complete lack of correlation between two variables is indicated by a correlation coefficient that is close to what value?

Answer 10

0

A correlation coefficient of 0 indicates a total lack of correlation; in other words, the two variables have no relationship with each other at all.

Question 11

As GPA increases, MCAT score also tends to increase. If a large increase in GPA only produces a relatively small increase in MCAT score, the correlation coefficient of this relationship would likely be between what two values?

Answer 11

between 0 and 0.5

A correlation coefficient in this range indicates the presence of a weak positive correlation (in other words, as one variable increases by a large amount, the other variable increases by a small amount).

Question 12

A strong negative correlation is indicated by a correlation coefficient near what value?

Answer 12

−1

The strongest possible negative correlation is indicated by a correlation coefficient of −1.

Question 13

Fill in the blank.

A weak negative correlation is indicated by a correlation coefficient between _______ and ________.

Answer 13

0 and −0.5

A weak negative correlation means that as one variable increases by a large amount, the other variable decreases by a small amount.

Question 14

What does a steeply sloping upward best-fit line in a graph of two variables indicate about the correlation coefficient?

Answer 14

1

This description corresponds to a strong positive correlation (as one variable increases, the other similarly increases). The strongest possible positive correlation is denoted by a correlation coefficient of 1.

Question 15

A correlation matrix is a table in which multiple variables are plotted along both the columns and rows of the table. Each cell then shows the correlation coefficient between the variable listed for that column and that listed for that row. Correlation matrices are typically marked by a line of correlations of 1 running diagonally through them. Why?

Answer 15

This diagonal line exists because the correlation between a variable and itself is always 1.

Check this out yourself next time you see a correlation matrix!

Question 16

What is the term for a longitudinal study that follows a group of individuals sharing a common characteristic over time?

Answer 16

cohort study

Here, the group of individuals is termed a cohort. Cohorts may be similar in their birth year (a “birth cohort”), in whether they have some disease, in their early exposure to a toxin, or in many other ways.

Question 17

Fill in the blank.

Unlike a cohort study, a ________ study involves close, detailed analysis of an individual, small group, or situation.

Answer 17

case

This differs from a cohort study, which involves analysis of a larger group. Case studies are extensively used in medicine, especially for rare or previously unknown conditions (such as a deep dive into the case of a woman with a previously undiscovered type of tumor).

Question 18

What type of study is conducted at the population or community level and typically focuses on the risk factors for a disease or condition?

Answer 18

ecological study

Often, the population assessed in an ecological study is determined geographically. For instance, an epidemiological study of risk factors for infection by a new virus in South Korea would be an ecological study.

Question 19

What are research methods called that involve observing people or groups in their natural settings?

Answer 19

ethnographic methods

These methods often are used to gather qualitative data about societies, although they can also be used to obtain quantitative data. Ethnographic methods are extensively used by anthropologists and some sociologists.

Question 20

Fill in the blank.

________ _______ is a research method that involves analyzing the words and (sometimes) images from websites, documents, works of art, or other bodies of language.

Answer 20

Content analysis

This method has been used increasingly often since the advent of computing tools that allow for easy analysis of text. (If you’ve ever seen a word cloud, that is an example of content analysis.)

Question 21

True or false.

Experimental studies are often a good way to study ecological factors at the neighborhood or community level, such as residential segregation.

Answer 21

False

Experimental studies at the neighborhood or community level are often unethical and typically impossible. (For instance, an experimental study of residential segregation would need to place some people in segregated areas and other people in areas that are not segregated, which is both not feasible and unethical.)

Question 22

Define:

survey methods

Answer 22

These are research methods intended to gather large amounts of data from subjects, often via tools such as questionnaires.

Question 23

Name three advantages of survey methods.

Answer 23

1. relatively cheap to use
2. relatively easy to implement (imagine how much simpler it is to write up a short survey than to design an experimental study!)
3. can reach a much larger sample size than a typical experimental trial

Question 24

Fill in the blank.

All but the very largest surveys typically are administered to a smaller ________ with the goal of reflecting the entire ________.

Answer 24

sample, population

The exceptions to this rule are large surveys like the U.S. Census, which aim to evaluate the entire population. (In those cases, then, the sample is the population.)

Question 25

What is critical about the surveyed sample for the results of a survey to accurately reflect a population?

Answer 25

representative

For instance, if the population we are trying to understand contains both men and women, it would be unrepresentative (and methodologically flawed) to survey only men.

Question 26

True or false.

All survey samples must include individuals from all wealth quintiles (from the wealthiest to the most impoverished).

Answer 26

False

This depends entirely on what the survey is aiming to study! For example, a survey focused solely on those below the poverty line would not need to include wealthy individuals to be representative.

Question 27

In a given population, 68% of the heads of household are renters, while 32% are homeowners. In a survey of heads of household with a sample size of 5,000 people, how many should be homeowners?

Answer 27

1,600

A perfectly representative sample should mirror the demographics of the population being evaluated. An easy way to obtain this answer is to realize that 32% of 10,000 would be 3,200, so 32% of 5,000 must be half of that: 1,600.

Question 28

What is the concept in research called that emphasizes the importance of knowing the order of events to understand causal relationships?

Answer 28

temporality

This concept follows from the logical idea that a cause must always precede its effect.

Question 29

Define:

a questionnaire

Answer 29

A list of questions devised by researchers and administered to or sent to a sample of people.

Question 30

What is self-reporting bias?

Answer 30

Also known as response bias, is a general term for a set of biases that cause survey subjects to respond inaccurately to survey questions.

Examples of self-reporting bias include social desirability bias and acquiescence bias.

Question 31

What is the tendency to agree with a statement when uncertain called?

Answer 31

acquiescence bias

You’ve probably experienced this before: you’re asked a question that you aren’t fully paying attention to or don’t really care about, and you reflexively say “yeah, sure.” This is a major problem that must be accounted for in surveys.

Question 32

How can researchers mitigate the effect of acquiescence bias in a questionnaire?

Answer 32

Include questions that have opposite meanings.

Acquiescence bias is the tendency to answer “yes” when uncertain or uninvested in a question. If questions with opposite meanings are asked, participants who answer “yes” to both can be identified, and those results can be thrown out or otherwise accounted for.

Question 33

What type of self-reporting bias is especially common when individuals are asked about their salaries?

Answer 33

social desirability bias

This is the tendency to answer questions in a way that make us look or feel better about ourselves. While salary is a classic example, this bias appears in questions about everything from one’s height to social and political issues.

Question 34

A person is answering a survey about a political candidate. The only thing the person knows about the candidate is that he is well-dressed and speaks coherently. The survey respondent therefore assumes that the candidate is a good person. This exemplifies what bias?

Answer 34

halo effect

The halo effect refers to a cognitive bias in which a person extrapolates from positive impressions about one aspect of a person or situation, usually resulting in an assumption that all facets of that person or situation are good/positive.

Question 35

What is the difference between leniency bias and harshness bias?

Answer 35

• Leniency bias refers to the tendency to answer every question leniently (that is, to be “too nice” in one’s answers).
• Harshness bias refers to the opposite: the tendency to answer every question harshly, or be “too mean” in one’s answers.

Question 36

This type of scale, used extensively in surveys, asks respondents to rate their level of agreement or disagreement with an item.

Answer 36

Likert scale

For example, a 5-item Likert scale may consist of the responses “strongly disagree,” “disagree,” “neither agree nor disagree,” “agree,” and “strongly agree.”

Question 37

What term in epidemiology refers to the number of new cases of a disease per unit of population over time?

Answer 37

incidence

For instance, the incidence of a particular cancer may be an average of 3 new cases per 10,000 people annually.

Note that epidemiology refers to the study of disease and its spread.

Question 38

What term in epidemiology refers to the proportion of people who have a given condition or disease at a given time?

Answer 38

prevalence

For instance, the current prevalence of a particular cancer may be 23 people who have the cancer for every 10,000 people.

Question 39

Which value is likely to be higher: the annual incidence rate of human immunodeficiency virus (HIV) or the prevalence rate of HIV?

Answer 39

prevalence rate of HIV

Since the incidence rate refers only to new cases of HIV developed over the previous year, while the prevalence rate includes everyone with HIV (even those who acquired the virus prior to the previous year), the prevalence rate should be higher.

Question 40

Studies of what population have been integral to our understanding of the classic “nature vs. nurture” debate?

Answer 40

twins

Twin studies have been absolutely crucial to our understanding of the roles played by nature (genetics) versus nurture (one’s environment). Since identical twins share the same genetics, twins raised in different environments allow us to isolate the effects of the “nurture” side.

Question 41

Fill in the blank.

Monozygotic twins share essentially ____% of their genes.

Answer 41

100

Monozygotic, or single-zygote, twins are also known as identical twins. Apart from the influence of rare phenomena such as mutations during development, these twins share an identical genetic code.

Question 42

Fill in the blank.

Dizygotic twins share ____% of their genes.

Answer 42

50

Dizygotic, or double-zygote, twins are also known as fraternal twins. Genetically, these twins are no different from any non-twin siblings: they share approximately 50% of the same genes.

Question 43

True or false.

If twins who were adopted into different families exhibit dramatically different interests, this supports the “nurture” side of the nature vs. nurture debate.

Answer 43

True

In adoption studies such as the one mentioned here, differences between the twins constitute evidence of “nurture” (the impact of environment rather than genetics).

Question 44

Name the three fundamental principles of research ethics.

Answer 44

1. Respect for persons
2. Beneficence
3. Justice

The rules of research ethics (such as the need to obtain informed consent) are all intended to uphold these three principles.

Question 45

Describe the ethical principle of beneficence in research.

Answer 45

The principle of maximizing the good that is done and minimizing the harm to participants.

This does not mean that participants cannot be harmed at all, but rather that any harm done must be as minimal as possible to achieve the planned benefits of the study.

Question 46

Describe the ethical principle of justice in research.

Answer 46

Refers to the obligation to distribute the burdens and benefits of research fairly.

Regarding burdens, this means that it would be unethical to conduct a study of a new medication on, say, orphans just because orphans are easier to exploit.

Regarding benefits, it means that the information learned from research should not be hoarded by any group (for instance, the rich).

Question 47

In the infamous Tuskegee Syphilis Study, 600 black men (many impoverished and over half with untreated syphilis) were monitored for over 40 years while being misled about the actual purpose of the study. Even when penicillin was found to effectively treat syphilis, these men were still not given penicillin. Which principle(s) of research ethics did this violate?

Answer 47

all three principles

The Tuskegee study is one of the most egregious examples of a lack of research ethics in modern American history. It violated respect for persons (by not obtaining informed consent), beneficence (by not minimizing harm to participants), and justice (by focusing on a vulnerable population).

Question 48

True or false.

Ethical approval committees never approve proposed research studies that involve inflicting pain on subjects.

Answer 48

False

Studies are absolutely allowed to inflict pain as long as 1) it is the minimum amount of pain necessary to achieve the study’s goals and 2) the subjects provide informed consent.

(In fact, Clara, the author of this card, once participated in a study that involved shocking participants inside an fMRI machine. That was a terrible time, but $20 is $20, I guess.)

Question 49

True or false.

It is unethical for researchers to include subjects with psychological disorders in their study samples.

Answer 49

False

Research studies include subjects with psychological disorders all the time! Again, it is simply extremely important that these subjects be able to provide informed consent.

Question 50

Fill in the blank.

Research involving human subjects can be made more difficult by the ________ _______, which is the principle that people often change their behavior when they know they are being observed.

Answer 50

Hawthorne effect

This effect was first noticed when observing workers in a factory for research involving productivity. Predictably, these workers worked differently (harder) because they knew they were being watched.

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