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Any collection of measurements or values
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| Single characteristic being mesured or changed |
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| data contingin measurements from a single variable |
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| contains mesurements from two variables |
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| contains data measured from three or more variables |
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one that takes on values representing categoreis or descriptions as opposed to numerical values.
ie. zip codes |
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| one that takes on numerical values. the values can be used in computations. |
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quantitative (one with numerical value) variable in which there are gaps between the possible values of the variable
ie. number of residents in a household (a calcuable value ie. 300 jelly beans in a bag of jelly belly's) |
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quantitative variable for which ther is an infinite number of possible values with no gaps between the values.
Ie. length of residence. Ie. Time. Ie. Number/time line...the distance between two points in infinate and continuous. you could divide forever and still have there be space inbetween. SO the amount of time that a resident lives in the home. |
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| collection of ALL subjects to be studied. |
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| The sub-collection of subjects drawn from WITHIN a given population |
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| Data being collected from every single member of the population bieng studied. |
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| a sample is drawn from a populaiton in such a way that every group of n subjects is the population is equally likely to be choosen. |
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a random sample collected from an oredered population by randomly choosing one of the first K subjects and selecting every Kth subject thereafter.
ie. on an assembly line she inspects the fith object and then every fifth object there aftere. |
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A population is broken into several groups and then a simple random sample is collected from with in each group.
I.e Doing a political pole we select 300 democrats, independents and republicans. we then do a simple random sample from within each strata and perform the evaluation. |
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Taken by dividing the population into several groups and then picking a simple random sample of the group and then sample each of the individual in the selected group.
IE Thirty flights are going out. Five flights are randomly choosen, each person on those five flights are evaluated. |
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| Cluster Sample: Story problem |
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| The pastor of a large church wishes to know what proportion of his congregation would be interested in a new outreach opportunity. Since the church is so large, he decides to collect a sample by randomly selecting 25 of the 100 active small group classes and asking all members of those 25 classes if they would support the new outreach program. |
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| Simple Random: Story Problem |
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| A county judge wishes to determine how many of the defendants that she sees have a high-school diploma. In order to collect a sample from her docket, she has her clerk use the computer to randomly select 40 case numbers and then checks the educational background of those defendants. |
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| Systematic Sample: Story Problem |
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| Workers for a consumer survey corporation collect data at a local mall by selecting a strategic location and then randomly selecting one of the first 50 people who walk by to ask to take the survey. They then ask every 50th person who walks by to complete the survey. |
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| Stratified Sample: Story Problem |
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| A golf pro shop wants to determine the average amount of money spent by the average customer. They suspect that men spend more in the shop than women. They therefore divide their customers into two groups: men and women. They then randomly select 40 of the male and 35 of the female customers and examine their most recent purchase. |
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| Specific characteristecs are seen and measured but NO ATTEMPT TO CHANGE THESE CHARACTERISTICS IS MADE |
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| treatment is applied and effects ont eh subjects is observed. |
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| Independent varibel, the value of which is verified by the experimenter |
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| Specific Combination of factor values |
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| Observational study:Story problem |
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| Sam wishes to determine the length of time that it takes a radish seed to germinate. He plants radishes in his garden, and continues his normal watering and weeding process. When the first radish sprouts emerge, Sam records the length of time that has elapsed. Is Sam conducting an observational study or an experiment? |
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| Expiriment: Story Problem |
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| Nancy is more ambitions than Sam. She wants to know if radish seeds can be made to germinate faster by altering the conditions in which they grow. To test this theory, Nancy decides that she will plant four groups of radish seeds. The first group will be watered and weeded as normal. The second group will be watered and weeded as well, but will in addition receive fertilizer every other day. The third group will be weeded as normal, but will receive twice as much water. Finally, the fourth group of radish seeds will be weeded as normal, receive fertilizer every other day, and get twice as much water. Nancy will record how long it takes each group of radish seeds to sprout. Is this an observational study or an experiment? |
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| Sampel collected by simply selecting the most easily available members of society |
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| Over-representation of one portion of a populaiton, or/and the under-representation of another. |
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| A quesiton phrased in such a way as to elicit a specific response. |
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| Voluntary Response Sample |
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| A sample in which people choose themselves whether or not to respond to a general request to participate. |
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the link between to or more variables if certain ones frequently appear together with certian values of the other.
ie. correlation between heigth and weight? does being taller cuase you to weigh more? or do they just happen to go together? |
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when, between two variables, the value of one of the variables causes the value of the otehr to change.
ie. measuring average driving speed and number of speeding tickets...it would be reasonable to say that there is a _________ between these to variable. Driving faster causes one to get more speeding tickets. |
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| Unmeasured variable that has an improtatn effect on the realtionship between variables in a study. |
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| Lurking Variable: Story Problem |
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In a study of fuel efficiency and its relationship to weight the Buick Estate Wagon appeared to be an anomaly. Although weighing much more than most cars in its class, the Buick Estate Wagon had a better fuel economy than it should have had in relation to these other cars. Further research indicated that Buick's recommended a higher tire inflation pressure than did the other car manufacturers. Identify the lurking variable in this study.
Tire pressure is the lurking variable. While it has an effect on gas mileage (higher pressure = better mileage) it was not included in the original study. |
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| Causation and correlation: Story Problem |
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A study of nutrition and TV ownership in Africa found that there was a high correlation between a family suffering from malnutrition and not owing a television set. A statistics student concludes that there is causation as well. That is, owning a television set leads to better nutrition. Critique this conclusion.
Solution
The student is confusing causation and correlation. While there may be correlation between owning a television and having good nutrition, it is not logical to conclude that having a TV improves nutrition. It is much more reasonable to conclude that there is a lurking variable in this study. Perhaps the economic status of the families studied is causing both the differences in nutrition and television ownership. |
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