descriptive research questions
Questions that examine and describe what already exists (e.g., how many people are involved in car accidents each year).
causal research questions
Questions that attempt to determine cause-and-effect relationships between variables.
nondirectional hypothesis
A hypothesis that states a relationship exists but does not specify the direction of the relationship.
directional hypothesis
A hypothesis that specifies the expected direction of the relationship between variables.
null hypothesis typically rejected
When the p value is less than or equal to the significance level (α).
p value
is a statistical measure indicating the likelihood of observing your data, or something more extreme, if the null hypothesis (no effect or no difference) were true, helping determine statistical significance
p value indicate the probability that the null hypothesis is true
No.
Type I error (α)
Rejecting a null hypothesis that is actually true (false positive).
Type II error (β)
Failing to reject a null hypothesis that is actually false (false negative).
alpha (α)
The probability of committing a Type I error.
Type II error when alpha is decreased
The probability of committing a Type II error increases.
statistical power
The likelihood of detecting a significant effect when one truly exists (1 − β).
power increases when…
Increasing alpha, increasing sample size, increasing effect size, minimizing error, using a one-tailed test, or using parametric statistics.
probability sampling
Sampling from a known population where each member has a known chance of selection.
nonprobability sampling
Sampling that does not involve random selection and often uses convenience samples.
simple random sampling
Every member of the population has an equal chance of being selected.
systematic sampling
Selecting every nth individual from a population list.
stratified random sampling
Dividing a population into subgroups and randomly sampling from each subgroup.
cluster sampling
a cost-effective survey method where a large population is divided into naturally occurring groups (clusters), like neighborhoods or schools, and then researchers randomly select a few of these clusters to study entirely, rather than surveying individuals from the whole population
multistage sampling
Sampling that occurs in multiple random stages (e.g., districts → schools → classes).
convenience sampling
Selecting participants who are easily accessible.
a non-probability research method where participants are chosen because they are easy and quick for the researcher to access, such as surveying people at a mall or online friends, offering speed and low cost but suffering from significant bias, as the sample often doesn’t represent the broader population.
purposeful sampling
a non-probability research technique where researchers strategically select participants or cases based on specific characteristics, knowledge, or experiences relevant to the study’s goals, aiming for rich, in-depth understanding rather than broad generalization, common in qualitative research to explore phenomena like cancer survivors’ experiences or teachers’ strategies with special needs students
quota sampling
A non-probability survey method where researchers select participants to match population proportions for specific traits (like age, gender) to ensure representation, but without random selection
internal validity
The degree to which changes in the dependent variable are caused by the independent variable.