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55 Cards in this Set
- Front
- Back
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Statistics is concerned with:
1. 2. |
1. processing and analysing data.
2. collecting, presenting and transforming data to assist decision makers. |
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Population
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A population consists of all the members of a group about which you want to draw a conclusion.
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Sample
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A sample is the proportion of the population selected for analysis.
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Parameter
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A parameter is a numerical measure that describes a characteristic of a population.
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Statistic
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A statistic is a numerical measure that describes a characteristic of a sample.
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What are the two branches of statistics?
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1. Descriptive Statistics
2. Inferential Statistics |
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What is descriptive statistics to do with?
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Collecting, summarising and presenting data.
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What are some examples of descriptive statistics?
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Collecting - survey
Presenting - tables and graphs Characterising - smaple mean |
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What is inferential statistics?
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Drawing conclusions about a population based only on sample data.
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What are some examples of inferential statistics?
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Estimation - estimate the populations mean weight using a sample mean weight.
Hypothesis testing - test the claim that the populations mean weight is 100kg. |
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What is univariate data?
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Data that contains only one variable.
ie: mean salaries |
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What is bivariate data?
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Data that contains only two variables.
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What is multivariate data?
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Data that records several variables for each 'individual'.
ie: table of salaries from each state. |
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What are the two forms of data?
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1. Primary Data
2. Secondary Data. |
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What is primary data? Give some forms.
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Primary data is data that is collected specifically to answer your question of interest.
Forms: observation, experiementail, survry |
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What is secondary data? Give it's forms.
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Secondary data is data that has been collected by somebody else for another purpose.
Forms: print or electronic (internet). |
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What is a statistical experiement?
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In an experiment, the researcher actively changes some characteristic of the units before the data is collected.
Therefore some of the variables values are under the control of the experimentor. |
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What is an observational study?
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Data is collected in an observational study id we passively record (observe) values from each unit.
ie: a survey. |
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What are the two types of data?
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1. Categorical
2. Numerical |
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What is categorical data and what are its levels of measurement?
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Categorical data values are selected from a sall group of categories.
Levels of measurement: 1. Ordinal 2. Nominal |
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What are ordinal categorical variables?
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Ordinal categorical values have categories that can be meaningfully ordered.
ie: service quality rating. |
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What are nominal categorical variables?
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Nominal categorical variables have categories that are equally meaningful.
ie: a students religion (christian, atheist, jewish) |
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What are the two forms of numerical variables?
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1. Discrete
2. Continuous |
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What is a discrete numerical variable?
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A variable whose values are whole numbers (counts)
eg: Number of items purchased by a customer at a supermarket. |
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What is a continuous numerical variable?
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A variable that may contain any value within some range.
Measured characteristics. eg: the amount of time that the customer spends in the supermarket. |
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What is the categorical 'trick' that could be encountered?
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Sometimes categorical variables are CODED as numbers when the data is recorded.
eg: 0 for male, 1 for female. The variable is still categorical dispite the numbers. |
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What is unstacked data?
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Data that is presented in a separate list for each group.
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What is stacked data?
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Data that is presented as a single list alonside a categorical variable.
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What are the formats used to show the relationship between two numerical values?
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- Correlation
- Least squares |
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What are the formats used to show the relationship between two categorical values?
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- Contingency table
- Conditional proportions |
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What is a census?
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Measurements that are made from every item in the target population.
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Why is completing a census often not possible?
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- the cost and time required
- recording some variables destroys the units ie: testing the strength of seatbels leaves them damaged. |
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What are the two types of samples used?
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1. non-probability sample
2. probability sample |
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What is a non-probability sample?
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Itmes included are chosen without regard to their probability of occurance.
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What are some examples of non-probability samples.
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1. judgement
2. chunk 3. quota 4. convenience |
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What is a probability sample?
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Items in the sample are chosen on the basis of known probabilities.
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Wha are some examples of probability samples?
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1. simple random
2. systematic 3. stratefied 4. cluster |
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What is a simple-random sample?
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Each unit has the same change of being selected.
A random mechanism is used to determine which units are included in the cycle. Selection may be with or without replacement. |
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How do you calculate a systematic sample?
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1. Decide on a sample size (n)
2. Divide the frame of N individuals into groups of k individuals. k=N/n 3. Randomly select one individual from the first group. 4. select every 'k'th individual from thereafter. |
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What does k = N/n mean?
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N = the size of the population (ie: 200)
n = the sample size (ie: 20) k = every 'k'th number is included in the sample. (ie: 200/20=10. So every 10th value is included in the sample). |
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What is strata?
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Subgroups
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How do you complete a stratefied sample?
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1. Divide the population into strata according to some common characteristic.
2. A simple random sample is selected from each strata, with sample sizes proportional to strata sizes. 3. samples from the strata are combined into one. |
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How do you perform a cluster sample?
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1. Divide the population into several 'clusters', each representative of the population.
2. a simple random sample of clusters is selected. NB: all items in the selected clusters can be used, or items can be chosen from a cluster using another probability samplling technique. |
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What is the advantage and disadvantage of simple random sampling and systematic sampling?
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A: simple to use.
D: May not be a good representation of the population's underlying characterisitcs. |
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What is the advantage of a stratefied sample?
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Ensures representation of individuals across the entire population.
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What is the advantage and disadvantage of cluster sampling?
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A: more cost-effective.
D: less efficient (need larger sample to acquire the same level of precision.) |
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What are the five types of survey errors?
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1. Coverage error
2. Non-response error 3. Sampling error 4. Instrument error 5. Interviewer error |
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What is a coverage erorr?
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It occurs when the sample is not selected from the target population but only a PART of the target population.
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What is non-response error?
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1. Failure to contact the individuals (ie: in a phone survey some numbers won't be answered)
2. Refusal to participate in the survey. 3. Refusal to answer specific questions (ie: salary) |
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What do coverage and non-response errors have in common?
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They are both the missing responses caused by failure to obtain information from some population members.
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What is a sampling error?
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The estimated mean or proportion is unlikely to be exactly the same as the underlying population parameter that is being estimated.
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What is a non-sampling error?
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A person may refuse to be part of a sample. A non-sampling error can be worse than a sampling error as:
- it is extremely difficult to assess their likely size - they often distort estimates by pulling them in one direction, the estimates are then biased. |
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What is an instrument error?
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This results from poorly designed questions. Different wordings can lead to different asnwers being given.
ie: leading question. |
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What is an interviewer error?
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This occurs when some characteristic of the interviewer (ie: gender, age) affects the way in which respondents answer questions.
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What are the four ways to evaluate survey worthiness?
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1. What is the purpose of the survey?
2. Are the questions appropriate and unambiguous? 3. Is the survey based on a probability sample? 4. Coverage error - is it an appropriate frame? |
