W2: Practice Questions for Concepts (Important!) Flashcards
What should any well-formulated research question contain? What is the most important?
(a) Grammatically expressed as a question, with a question mark “?” at the end.
(b) All relevant constructs to be investigated.
(c) Population relevant for these constructs and research context.
(d) Specify the general form of the relationship among constructs to be investigated by use of a term such as “associate”, “predict”, or “different” [Most important]
What do we mean by a population in psychological research? How is it defined? What is the size
Population
Complete set of all persons for whom the research question/research hypothesis is relevant.
Defined in terms of either:
(i) psychological construct (e.g., depression) or defined condition (e.g., people with epilepsy), which identifies a homogeneous grouping, or
(ii) the general population (when theory and the research question/hypothesis are not restricted to a homogeneous group)
Size
A research population can be theoretically infinite in size, or it may be finite.
What do we mean by a sample ? How is it defined
Sample
- finite set of people of size n
- selected from a relevant population
- to investigate the research question, and on whom we take measurements in order to undertake the research
How does a sample differ from a population in psychological research?
- A sample is a subset of people selected from the population.
- It is feasible that many different samples can be selected from the same population (but research typically use one)
How is a sample related to a population ?
Each sample is considered representative (not always) of the population in some way due to the way it is selected.
Sample is used to make inferences about relationships among constructs at the population level
What do we mean by a parameter in psychological research? What is its role?
Population Parameter
-
Quantitative summary characteristic of all people in a population that may define
- e.g., the average amount or average variability of some construct, or the strength of relationship between constructs.
- Regarded as having only one possible fixed value
- i.e., the population value
What do we mean by a statistic in psychological research? What is its role?
Sample statistic
- Quantitative summary characteristic of all people in one particular sample of size n drawn from the population
- Value of a sample statistic will vary from one sample to the next when different samples are selected from the same population
How does a statistic differ from a parameter
- Only one possible value of parameter
- Can be many different values of a statistic.
- Value of a parameter is always unknown (can’t be calculated, only estimated)
- Value of sample statistic is always known.
- Value of a sample statistic will almost certainly be different to the population parameter
How is a statistic related to a parameter ?
A sample statistic is related to a population parameter by:
- Value of the sample statistic being an estimate of value of the population parameter, and
- A statistical inference being made about the value of an unknown population parameter from the known value of a single sample statistic
What is the difference between peoples’ observed scores and their raw scores
The observed score and the raw score in sample data mean exactly the same thing
- Actual untransformed values recorded for each person when measuring a construct.
How does a raw score differ from a deviation score?
Deviation scores
- Value obtained from a raw (i.e., observed) score when some constant value is subtracted from it.
- The most typical form of a deviation score is when the sample mean is subtracted from each person’s raw score
- Any positive deviation score = Original raw score is above the sample mean
- Any negative deviation score = Original raw score is less than the sample mean
- When sample mean is used to create deviation scores, the deviation scores will have a mean of 0
How does a deviation score similar/differ from a Z score ?
Deviation
- Mean = 0
- SD = SD of sample raw scores
- i.e., creating deviation scores does not change the average amount of variability in the scores themselves
- Tell us whether a value is above or below the mean
- Do not tell us how far any value is from the mean.
Z-Scores
- Standardized deviation scores
- Also mean = 0
- SD = 1
- Z scores are calculated as deviation scores that have each been divided by the standard deviation
- Tell us whether a value is above or below the mean
- Tell us how far any value is from the mean.
Both deviation scores and Z scores can be regarded as ways of applying a transformation to raw scores.
How does a Z score differ from a standardised score ? How is Z calculated?
- Z scores = Particular kind of standardised score
- With mean = 0 and sd = 1
- Z scores are typically calculated by transforming raw score using the sample mean and sample standard deviation
- or the population mean and standard deviation can be used if they are known, e.g., like for IQ tests).
Bob’s raw score on a resilience measure is 23; Ali’s deviation score on the same measure is –4.
(a) Which one of the two people has greater resilience?
(b) What reason(s) did you base your answer on?
(c) What can you conclude about Ali’s level of resilience?
(a) Cannot say without knowning sample mean.
(b) Raw scores and deviation scores cannot be compared directly without knowing the value of the sample mean used to transform the original raw score into a deviation score.
(c) All we know is that Ali’s score is 4 units below the mean (but it is not clear what these 4 units represent, because the metric of this score has no specified scale)
Bob’s raw score on a resilience measure is 23; Ali’s deviation score on the same measure is –4. The sample mean is 35
(a) Which one of the two people has greater resilience?
Bob’s Raw:23
Ali’s Raw: 31
Bob’s deviation: -12
Ali’s devation: -4
Ali has 8 units higher than Bob
