CHAPTER 3 1 INTRODUCTION TO DATA COLLECTION 1

1. WHEN DECIDING WHAT DATA TO COLLECT, WE FIRST MUST DESCRIBE WHAT IT IS

IMPORTANT DEFINITIONS VARIABLE: A CHARACTERISTIC ABOUT EACH INDIVIDUAL ELEMENT OF A POPULATION OR SAMPLE.

POPULATION: THE ENTIRE GROUP THAT WE ARE INTERESTED IN SAMPLE: A SELECT NUMBER OF

EXAMPLE 1. A GROCERY STORE WANTS TO KNOW THE AVERAGE NUMBER OF ITEMS THAT

2. A TEAM OF BIOLOGIST WANTS TO KNOW THE AVERAGE WEIGHT OF FISH IN

FORMS OF DATA COLLECTION • THERE ARE THREE MAIN FORMS OF DATA COLLECTION: •

SURVEYS • AN INVESTIGATION ABOUT THE CHARACTERISTICS OF A GIVEN POPULATION BY MEANS OF

PROS AND CONS TO SURVEYS A FEW PROS TO SURVEYS A FEW CONS TO

OBSERVATIONAL STUDIES • IN THIS TYPE OF STUDY, RESEARCHERS OBSERVE THE BEHAVIOR OF THE

EXPERIMENTS • IN AN EXPERIMENT, RESEARCHERS MANIPULATE THE VARIABLES TO TRY TO DETERMINE THE

STATISTICAL QUESTIONS • TO TELL IF A QUESTION IS STATISTICAL OR NOT, YOU NEED

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CHAPTER 3. 1 INTRODUCTION TO DATA COLLECTION

1. WHEN DECIDING WHAT DATA TO COLLECT, WE FIRST MUST DESCRIBE WHAT IT IS THAT WE ARE LOOKING FOR. TO DO THIS, WE NEED TO ASK THE FOLLOWING QUESTIONS WHENEVER WE DECIDE TO COLLECT DATA FOR SOMETHING. 2. WHAT DO I WANT TO KNOW? • WHAT IS MY POPULATION • WHAT IS MY SAMPLE • WHAT AM I MEASURING 3. HOW WILL I COLLECT THE DATA • WHAT IS GOOD DATA, WHAT IS BAD DATA • DO I HAVE ACCURATE DATA • WHAT METHODS WILL I USE TO COLLECT DATA 4. WHAT IS MY TIME FRAME FOR COLLECTING DATA 5. DOES MY DATA MAKE SENSE

IMPORTANT DEFINITIONS VARIABLE: A CHARACTERISTIC ABOUT EACH INDIVIDUAL ELEMENT OF A POPULATION OR SAMPLE. DATA (SINGULAR): THE VALUE OF THE VARIABLE ASSOCIATED WITH ONE ELEMENT OF A POPULATION OR SAMPLE. THIS VALUE MAY BE A NUMBER, A WORD, OR A SYMBOL. DATA (PLURAL): THE SET OF VALUES COLLECTED FOR THE VARIABLE FROM EACH OF THE ELEMENTS BELONGING TO THE SAMPLE. EXPERIMENT: A PLANNED ACTIVITY WHOSE RESULTS YIELD A SET OF DATA. PARAMETER: A NUMERICAL VALUE SUMMARIZING ALL THE DATA OF AN ENTIRE POPULATION.

POPULATION: THE ENTIRE GROUP THAT WE ARE INTERESTED IN SAMPLE: A SELECT NUMBER OF SUBJECTS FROM THE ENTIRE GROUP THAT WE ARE INTERESTED IN PARAMETER OF INTEREST: THE THINGS THAT WE ARE INTERESTED IN KNOWING ABOUT THE POPULATION

EXAMPLE 1. A GROCERY STORE WANTS TO KNOW THE AVERAGE NUMBER OF ITEMS THAT SHOPPERS PURCHASE IN EACH VISIT TO THE STORE. THEY DECIDE TO COUNT THE ITEMS IN THE CART OF EVERY TWENTIETH PERSON THROUGH THE CHECK STAND. POPULATION : SAMPLE: PARAMETER OF INTEREST :

2. A TEAM OF BIOLOGIST WANTS TO KNOW THE AVERAGE WEIGHT OF FISH IN A LAKE. THEY DECIDE TO DROP A NET AND MEASURE ALL THE FISH CAUGHT IN THREE DIFFERENT LOCATIONS IN THE LAKE. POPULATION : SAMPLE: PARAMETER OF INTEREST :

FORMS OF DATA COLLECTION • THERE ARE THREE MAIN FORMS OF DATA COLLECTION: • SURVEYS • OBSERVATION STUDIES • EXPERIMENTS

SURVEYS • AN INVESTIGATION ABOUT THE CHARACTERISTICS OF A GIVEN POPULATION BY MEANS OF COLLECTING DATA FROM A SAMPLE OF THAT POPULATION AND ESTIMATING THEIR CHARACTERISTICS THROUGH THE SYSTEMATIC USE OF STATISTICAL METHODOLOGY. • SURVEYS ARE USUALLY USED WHEN YOU WANT TO KNOW: • HOW PEOPLE FEEL • WHAT THEIR PREFERENCES ARE • WHAT THEY OWN • HOW MUCH MONEY THEY MAKE • ETC • QUESTIONNAIRES ARE THE MAIN FORM OF SURVEYS

PROS AND CONS TO SURVEYS A FEW PROS TO SURVEYS A FEW CONS TO SURVEYS • GENERALLY QUICK FOR PARTICIPANT • SURVEYOR BIAS • EASY TO COLLECT DATA • HONESTY • CATEGORICAL DATA – EASY TO DISPLAY IN BAR GRAPH OR PIE CHART • LACK OF DEPTH

OBSERVATIONAL STUDIES • IN THIS TYPE OF STUDY, RESEARCHERS OBSERVE THE BEHAVIOR OF THE PARTICIPANTS/SUBJECTS WITHOUT TRYING TO INFLUENCE IT IN ANY WAY SO THEY CAN LEARN ABOUT THE PARAMETER OF INTEREST.

EXPERIMENTS • IN AN EXPERIMENT, RESEARCHERS MANIPULATE THE VARIABLES TO TRY TO DETERMINE THE CAUSE AND EFFECT • CONTROL • VARIABLE

EXAMPLE:

STATISTICAL QUESTIONS • TO TELL IF A QUESTION IS STATISTICAL OR NOT, YOU NEED TO DETERMINE IF THE QUESTION HAS VARIABILITY IN THE ANSWER OR IF IT IS JUST A SINGLE ANSWER. ALSO IT SHOULD MAKE SENSE TO DO A STATISTICAL ANALYSIS TO THE QUESTION. • EXAMPLES: • HOW FAR IS IT FROM BOISE TO MIAMI? • HOW TALL ARE THE STUDENTS IN MR. CARPENTER’S CLASS? • ARE THE TREES IN BOISE TALLER THAN THE TREES IN MERIDIAN? • WHAT IS THE LONGEST TIME YOU CAN HOLD YOUR BREATH FOR?