1 3 Data collection and sampling techniques Note

1 -3: Data collection and sampling techniques Note: This Power. Point is only a summary and your main source should be the book.

1 -3: Data collection and sampling techniques Data collection Surveys Telephone Mail questionnaire Observational and Experimental Studies Personal interviews Note: This Power. Point is only a summary and your main source should be the book.

To obtain samples that are unbiased , statisticians use four methods of sampling : Some Sampling Techniques Random sampling Systematic sampling Stratified sampling Cluster sampling Note: This Power. Point is only a summary and your main source should be the book.

sampling techniques: • 1 - Random Sampling : are selected by using chance methods or random numbers. For example: Select random sample of 15 subjects out of 85 subjects Note: This Power. Point is only a summary and your main source should be the book.

A: 12, 27, 75, 95, 62, 57, 13, 31, 06, 16, 49, 46, 71, 53, 41, 02 Note: This Power. Point is only a summary and your main source should be the book.

sampling techniques: 2 - Systematic Sampling : are obtained by numbering each value in the population and then selecting the kth value. For example: Ø There are 50 students in your class. Ø You want a sample of 10. n=10 Ø You have a class listing in alphabetical order. Ø Divide 50 by 10 , you will get 5. N=50 K=N/n= 50/10=5 Ø Randomly select any number between 1 and 5. That is your starting number. From there select every 5 th name until you reach the last one. Note: This Power. Point is only a summary and your main source should be the book.

Note: This Power. Point is only a summary and your main source should be the book.

sampling techniques: 3 -Stratified samples: are selected by dividing the population into groups (strata) according to some characteristic and then taking samples from each group. • for example: A researcher select a random sample from each gender to check their blood pressure.

sampling techniques: 4 -Cluster samples are selected by dividing the population into groups and then taking samples of the groups. such as geographic area or schools in a large school district. For example : In a large school district , all teachers from two building are interviewed to determine whether they believe the students have less homework to do now than in previous years. • Randomly selected 2 clusters Population divided into 4 clusters Randomly

Summary of sampling techniques • • • 1 -Random : random number generator. 2 -Systematic : every kth subject. 3 -Stratified : divide population into group called “strata”. 4 -Cluster : use intact groups. 5 -Convenient : mall surveys. Note: This Power. Point is only a summary and your main source should be the book.

1 -4: Observational and Experimental Studies

Observational Study: The researcher merely observes what is happening or what has happened in the past and tries to draw conclusions based on these observations. For example: ” if a researcher records how many students are wearing glasses in the Science building over a period of time “. Note: This Power. Point is only a summary and your main source should be the book.

Experimental Studies: • the researcher manipulates one of the variables and tries to determine how the manipulation influences other variables. for Example: 1 - Patients were randomly assigned to two groups: one group was given drug A and the other group was given drug B to determine if the drug has an effect on patient’s blood pressure. 2 -An Instructor has Three Teaching methods , he wants to apply a best method by seeing students grades. Note: This Power. Point is only a summary and your main source should be the book.

v In a true experimental study, the subjects should be assigned to groups randomly. If this is not possible and a researcher uses intact groups, then he is performing a quasi-experimental study. Note: This Power. Point is only a summary and your main source should be the book.

Experimental studies usually include two types of variable The Independent variable or The Dependent variable or Explanatory variable Outcome variable is the one that is being manipulated by the researcher. is the resultant variable. Note: This Power. Point is only a summary and your main source should be the book.

For example: 1 - Patients were randomly assigned to two groups: one group was given drug A and the other group was given drug B to determine if the drug has an effect on patient’s blood pressure. Independent Variable Drug A , Drug B Dependent Variabe Blood pressure Note: Statistical studies usually include one or more independent variables and one dependent variable. Note: This Power. Point is only a summary and your main source should be the book.

• A confounding variable is the variable that influences the dependent or outcome variable but cannot be separated from the independent variable. For Example : subjects on exercise program may improve their diet and perhaps that improve their health in other ways not due to exercise alone. Then diet becomes confounding variable. Exercise Diet influence Weight confounding Note: This Power. Point is only a summary and your main source should be the book.

cigarette Age influence Health confounding Note: This Power. Point is only a summary and your main source should be the book.

Types of group Treatment Group The group that received the special instruction. Control Group The group that dose not received the special instruction. Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics Suspect sample Ambiguous Averages changing Subject Detached Statistic Misleading Graphs Faulty Survey Question

1 -5: Uses and Missuses of statistics 1 - Suspect sample: Ø small samples Ø convenience sample Ø volunteer sample For example: ” if 4 doctors were surveyed from 100 doctors”. Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics 2 - Ambiguous Averages • measures that are loosely called averages are the mean, median, mode and midrange. People who know this can without lying , select one of them to support their position. Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics 3 - changing Subject can occur when different values are used to represent the same data. For example: if one political candidate say “ I will increase salaries a mere 3%” And another one say “I will increase salaries a whapping 6, 000 $” And 3% =6, 000 Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics 4 -Detached Statistic it is the one in which no comparison is made. For example, one may say that “Our cookies has onethird fewer calories” Here, fewer than what? Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics 5 -Implied connection Usage of words such as may, suggest or some that imply connections but there is no guarantee For example: ” Eating fish may help to reduce your cholesterol”. may some Might help Some people Note: This Power. Point is only a summary and your main source should be the book.

1 -5: Uses and Missuses of statistics 6 -Misleading Graphs if graphs are drawn inappropriately, they can misrepresent the data and lead to false conclusions.

1 -5: Uses and Missuses of statistics 7 - Faulty Survey Question should be sure that the questions are properly written since the way questions are phrased can influence the way people answer them. Note: This Power. Point is only a summary and your main source should be the book.

Note: This Power. Point is only a summary and your main source should be the book.