Part 02  What is Statistical bias ?
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You are advised to watch the E02 video but it is not necessary. Read the following statement and try to answer the following questions.
“Let’s say that you have a fat cat and each morning is taking a walk from your house to the house of your neighborhood. Suppose that this distance is almost a straight line without any major obstacles. You think that if you knew the distance that each time your cat makes, it will help you to determine her diet. Suppose that you can see where your cat put her paws”
*Note that in the end you will be asked to give some general information about you e.g. Gender, age (ranges). These information will be used only for general statistics.
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Question 1 of 7
1. Question
You get anxious about your little experiment. You are trying to get all things in place. Which (choose one) of the following options must do before your cat goes out?
Correct
Right!
Incorrect
oh! Dont mind. Even from our errors we can learn a lot! So, if you have chosen to use the old measure device, you may introduced into your results high statistical error, because your measure device may have been stretched out the distance of e.g. “1 to 2″ which can be different than the distance between “3 and 4″. So, if you are forced to change your measuring device in the middle of your experiment with a new one, your old observations will not match the new ones. That is the reason that you must have a new measure device which have not been stretched out from years of use, as well a new pen, and a paper. You may also can see the BBC documentary and it is prerequisite that the “cat door” must be open, otherwise, you could not have observations to write down!

Question 2 of 7
2. Question
Now, your cat has gone out for her daily walk. After a while, you have wroten down the distance she walked (according to her paw traces). In order to have statistics reliable enough, that is, with low statistical bias or error, how many observations/distance measures do you believe you must write down in order to calculate a good diet for your cat?
Correct
Right! I think you have get an idea what statistics are about! Please stay in tune for more StatQuiz or Xplained Stat Videos
Incorrect
Note that We are discussing about statistics. How can you have the optimal result with the best utilization of your time and effort! Don’t forget that! Statistics were invented as a shortcut. For general statistics, no more than 1000 observations are needed, most of times, see for example exit polls that uses most of times no more than 3000 observations to predict the final result. So, in this example, very few observations will tend to have high statistical error/bias due to the reason that they are very few! Your cat may have not walked so “straight” the distance between you house and the house of your neighborhood. !0 to 20 observations are still few observations. You may have a reliable result, but it will depend on how “randomly” your cat have walked!
50 to 100 observations for calculating her diet is more than enough. 500 or more observations are considered as very much here. Yes, you may get even more reliable results, but you do an experiment for your fun, not for scientific reasons!Hint
We are discussing about statistics. How can you have the optimal result with the best utilization of your time and effort! Don’t forget that!

Question 3 of 7
3. Question
You checked your writings/results and you find out that you have a couple of observations that are high enough, that is, it appears that your cat walked a lot more, lets say around 7 meters instead of 45 meters. You know that at these times your cat did a longer round to reach the house of your neighborhood than other times. You think, that these higher numbers, in comparison with the previous ones, must be…
Correct
You may calculate two outcomes, one by using all of your observations and one without taking into considerations these higher numbers/observations. You will decide upon the final results. The final results may do not have a high difference after all.
Incorrect
You may calculate two outcomes, one by using all of your observations and one without taking into considerations these higher numbers/observations. You will decide upon the final results. The final results may do not have a high difference after all.

Question 4 of 7
4. Question
if you asked your neighborhood to participate in your little experiment by also measuring the distance that your cat have walked from your house to his/her house, do you think, this will make your results more reliable by reducing statistical error?
Correct
So, you understand that if you compare both results, and find out high gaps between them, maybe they can be attributed to error on one of the measuring devices. Also, you understand that your little experiment can increase its reliability by reducing statistical error by adding an extra observer which can replicate your results.
Incorrect
By using an extra observer, your little experiment increases its reliability by reducing statistical error. You may felt ill some time or you may forgot to take into considerations some “traces of your cat paws” or the way that you use your measuring device may is not the better one! So, by comparing your results with those of another person with different personal characteristics than you, it can save you time and it will increase the reliability of your experiment. Moreover, it is better your neighborhood not have the exactly same measuring device (it depends!) but a similar one. So, if you compare both results, and find out high gaps between them, maybe they can be attributed to error on one of the measuring devices.

Question 5 of 7
5. Question
If your cat had an accident and she cannot walk anymore, what are you willing to do about your little experiment?
Correct
I know, it is sad about what happened to your cat, very sad. So, you must stop your experiment, there is no reason to keep these results. You may keep them for just keeping a record/history. However, don’t get down now! Your cat needs you, and you may think another experiment in order to receive your cat a proper diet! She needs you now more than ever! So… i am waiting your comments and ideas for a new cat experiment!
Incorrect
I know, it is sad about what happened to your cat, very sad. So, you must stop your experiment, there is no reason to keep these results. You may keep them for just keeping a record/history. However, don’t get down now! Your cat needs you, and you may think another experiment in order to receive your cat a proper diet! She needs you now more than ever! So… i am waiting your comments and ideas for a new cat experiment!

Question 6 of 7
6. Question
One day you were ill and you could not write down the distance that your cat walked. However, your neighborhood did write it down. What do you think you must do now?
Correct
1st and 2nd option can be applied. The option to replace the missing value with the total mean of your observations is not the most reliable one. If no other record were kept for this day, this could be a solution. An ongoing discussion exists on how to treat missing values. It is not an easy thing!
Incorrect
1st and 2nd option can be applied. The option to replace the missing value with the total mean of your observations is not the most reliable one. If no other record were kept for this day, this could be a solution. An ongoing discussion exists on how to treat missing values. It is not an easy thing!

Question 7 of 7
7. Question
So, now you have your results from your observations. You calculated the total mean of the distance that your cat has walked. Let’s say that this number is 5.60 meters (or points or whatever is your distance measurement unit). How can you proceed now in order to adjust her diet?
Correct
Yes, All choices can be applied. There is no an absolute right or wrong here. You have a real problem here because you did not designed very thoroughly in the very beggining. Therefore, the best you can do now is to redesign your though and to find a way to solve your problem. Statistical analyses is full of problems as life! You may think a better idea than the current ones! I am urgently waiting to receive it in my comments! I will add it to the Statquiz and my Xplained Stat Videos!
Incorrect
Yes, All choices can be applied. There is no an absolute right or wrong here. You have a real problem here because you did not designed very thoroughly in the very beggining. Therefore, the best you can do now is to redesign your though and to find a way to solve your problem. Statistical analyses is full of problems as life! You may think a better idea than the current ones! I am urgently waiting to receive it in my comments! I will add it to the Statquiz and my Xplained Stat Videos!