Introduction to Statistics Notes Prepared by Nurul Emyza Zahidi INTRODUCTION TO STATISTICS Statistics Study of how information is collected, presented, analysed and interpreted for use in making decisions. Descriptive Statistics Summarizing data in the form of graphs, charts or table and techniques for obtaining numerical summaries such as mean, median, mode, variance and standard deviation. Inferential Statistics Techniques used to make or draw conclusions about a population from the selected samples. Primary Data which gathered by the researcher himself. Data Observation or information that have been recorded or collected. Secondary Data is already being collected, recorded or published by someone. Ordinal Scale Use ranks to give ordering to data of this type of scale. *Qualitative data Nominal Scale Classifies data in the form of labels or categories. *Qualitative data Interval Scale Ordered scale in which the difference between measurements is meaningful. *Quantitative data Scales of measurements Ratio Scale Ordered scale with meaningful difference between measurement and also in addition he exists a true or fixed zero point. *Quantitative data NEZ/ASAH/NAK/SBS/ISS 1 Introduction to Statistics Notes Prepared by Nurul Emyza Zahidi SAMPLING TECHNIQUE Probability Sampling Every elements in a pop. has an equal chances of being selected Sampling frame easily obtained 1. Simple Random Sampling Sample is drawn randomly from a population. 2 basic methods: 1. Lottery Method 2. Random Number Table Advantage Very easy to use Disadvantage A very unrepresentative sample may result if the population is not homogeneous The numbering of the population may prove very laborious and cumbersome Requires only the least knowledge about a population in advance 2. Systematic Sampling Sample is drawn systematically selected from a population. Advantage Disadvantage Systematic samples can be chosen much May results in systematic bias more speedily Simple and easy to draw samples and May results in unrepresentative sample if hence widely used the population is not homogeneous 3. Stratified Sampling Population is divided into group (strata) and sample is selected from each of the group(strata) Advantage Disadvantage Stratified samples can represent the If stratified lists are not available, they can population since from each stratum there be costly to prepare are representatives A respective study can also be done on Requires accurate information on elements within the same strata proportion in each stratum 4. Cluster Sampling Population is divided into group (cluster) and sample consists of all elements from selected group(cluster) Advantage The cost of data collection is low if the clusters are geographically defined Disadvantage May result in an unrepresentative sample if the chosen clusters do not consist of all the subgroups in a population Requires the listing of all clusters but of May have prior knowledge of all the clusters individuals only within cluster 5. Multi-stage Sampling Divide large population into stages to make the sampling process more practical. Advantage This technique is suitable especially if the population of interest is very large Cost of sampling can be reduced with little lost information Disadvantage Sampling process may become complex Little loss of information cannot be avoided NEZ/ASAH/NAK/SBS/ISS 2 Introduction to Statistics Notes Prepared by Nurul Emyza Zahidi Non-probability Sampling Sampling frames difficult to obtained Generalisation about the population is not the main issue 1. Convenience Sampling Researcher select the easiest population members from which to obtain a data. Advantage Disadvantage Very widely use in studies because of its Introduces bias in researcher’s convenience, easy and inexpensive classification of samples 2. Judgment Sampling Researcher use his/her judgement to select population members who are good prospects for accurate information. Advantage Disadvantage The cost is moderate, and sample Introduces bias in researcher’s guaranteed to meet a specific objective classification of samples 3. Quota Sampling Researcher prescribes number of people in each of several categories Advantage The procedure does not require any sampling frame Sampling process is simpler compared to other techniques of sampling Disadvantage The procedure is not random Interviewer bias cannot be avoided Personal Interview Interviewer asking questions to one or more respondents in face-to-face situation. Advantage The interviewer can clarify any terms that are not understood by respondents Disadvantage Very costly and time consuming Interviewer are assigned at a strategic location to observe and record respondents’ behaviour. Telephone Interview Interviewer asking questions to one or more respondents through telephone. Advantage Faster results since there is no travel time between consecutive interviews Disadvantage Only limited to respondents who have telephone facilities Observation Data Collection Techniques Advantage Observation avoids interviewer-interviewee bias Disadvantage The observers may wrongly interpret what the respondent are doing NEZ/ASAH/NAK/SBS/ISS 3 Introduction to Statistics Notes Prepared by Nurul Emyza Zahidi Designing a good questionnaire Questions must be in order Questions must be short and simple Try to minimize the use of openended questions Avoid very personal questions and confusing questions Questions are very brief and understandable Avoid vague/ambiguous words and leading questions NEZ/ASAH/NAK/SBS/ISS 4