Question

Which are paired designs and which are two independent random sample designs? For each #, it's one or the other...

#1 (a) Study of shopping at Wal-Mart. Study is on whether more go in non-grocery door than the grocery door? Study is done by counting the number of people entering each door from 7-9pm every Monday for 2 months.

(b) Study of shopping at Wal-Mart, but to collect data the number of people entering each door from 7-9pm on non-grocery and grocery at random and NOT collect both each time together. For example, do a non-grocery count this Monday from 7-9pm, then non-grocery again Tuesday from 7-9pm, and then grocery on Wednesday from 7-9pm, etc.

#2 (a) Study is on the effect of magnetic fields on healing times. To collect data you take 100 random individuals prick a single finger on each. Half of them you use magnetic field on and the others you don't. You record healing time.

(b) Study is on the effect of magnetic fields on healing times. On each of the 100 participants you prick one finger on each hand. Apply magnetic field to one finger and nothing to the other. You measure healing times for fingers.

#3 (a) Taste testing is done in which each participant tries coke and pepsi both and rates them both. (b) Taste testing is done in which each person just tastes one and rates it and some other random person tastes the other and rates it.

#4 (a) Study of whether more movies are rented at Redbox on Friday or Saturday nights. Record rental numbers every week for 6 months on each Friday and the Saturday right after it.

(b) Study of whether more movies are rented at Redbox on Friday or Saturday. To get the data you randomly pick 24 Friday’s and then randomly pick 24 Saturday’s and record rentals on each. Note, it is NOT necessary for them to one right after the other.

#5 (a) Randomly pick 50 items that have been produced and use method one on it, then randomly pick another 50 and use method two on it.

(b) Match two items up because they came off production line together. Apply method one to one of them and method two to the other.

Answer 1

Paired design if we use same set of population twice.

Two independent random sample design if we choose two sets of population independently i.e. not same population. These two may contain some common individuals or may not.

1.

(a) Paired design as we are taking same set of population (people entering from 7-9 pm on fixed days).

(b) Independent random sample designs as we are taking independent sets of population.

2.

(a) Independent random sample designs as half of them are checked in magnetic field on and the others are not.

(b) Paired design as all are checked in magnetic field once and without magnetic field once.

3.

(a) Paired design as whose tastes Coke also tastes Pepsi also.

(b) Independent random sample designs as each participant tries either Coke or Pepsi and set of population to test Coke is different from that of Pepsi.

4.

(a) Paired design as two sets of population are dependent. Both the days are necessarily considered as consecutive days.

(b) Independent random sample designs as choice of population set (renter on days) are independent of choice of other.

5.

(a) Independent random sample designs as two methods are applied on two differently picked sets of items.

(b) Paired design as a method is applied on one and another on other where two matching items were considered.