PRR 844 Exercise - Lansing Riverfront Trail Use Estimates
PURPOSE: This exercise will provide practice in the analysis of observational data. It also illustrates the procedure for expanding from a time sample of observations to the population using either a simple random sample or stratified sample. The data were gathered by PRR 475 students using observations along the Lansing Riverfront Trail. We will use the 1996 observations.
Using the 30 observations at Aurelius and Kalamazoo access points on Lansing Riverfront Trail (in Trail96.xls file on Count96 page), answer the following questions:
1. How much use did the eastern section of the trail receive in October of 1996?
2. Where and when was use heaviest? How was use distributed across the two access sites and by time of day and day of week?
3. Who uses the trail? Report the percentage of use by type of use, user characteristics, etc.
MATERIALS:
a. The HINTS page suggests how to do this exercise. Try it without consulting the hints first.
b. 'Lansing Riverfront Trail Study" summarizes purposes and study approach. Note especially the sampling strata - 30 of the planned observations were completed.
c. Observation form(s) including observation instructions, coding of variables and how use was operationally defined and measured. The data file has the hourly sums that were entered on the final "Summary Counts" form plus the variables in the box at top of the INSTRUCTION sheet.
- Hourly observation counts. Available in an Excel file in the course AFS space -- msu/course/prr/844/ trail96.xls. Use the 1996 data by selecting the 1996 tab at bottom. After completing 1996, you are welcome to try other years or combining data across years. We also made observations in 1995 and 1993 also.
- A summary instruction sheet for Excel is also in course AFS space as a WORD document (EXCEL.doc)
Format of your report: (Shouldn’t take more than 2 pages).
1. For each of the three questions /objectives, briefly explain how you generated the answers - call this section METHODS.
2. For each question/objective summarize the answer in a brief text, table, figure or combination of these - put these in a RESULTS section.
3. If you like, you may paste parts of the study summary page at front to yield a complete mini-report
EXERCISE DUE: April 12
HINTS ON THE ANALYSIS
1. ESTIMATING OCTOBER USE. There are many ways to do this, some right some wrong, and many better or worse. Note that the sampling design suggests the recommended approach using the 6 strata.
a. Use the sample to obtain an average use per hour (note the PEOPLE column has counts of observed trail users per hour. You can get an overall average (all observations) by using the AVERAGE function to average the PEOPLE column in Excel OR get averages by strata using the Pivot table command (use STRATA as row variable, LOCation as column and Average of PEOPLE in cells).
b. Expand from the sample to population. Figure out the total number of daylight hours in October (12 hour days * 31 days) or the number that fall into each of the six strata. Multiply the number of hours by the average use per hour computed in step a. Sum across strata if you compute by strata to get total October use.
2. ESTIMATING USE DISTRIBUTION AND TYPES OF USERS. You could repeat the procedures in (1) using numbers from the other columns on the data sheet in place of the PEOPLE column. For example, using the WHITE column would estimate number of "white" users. This would be very tedious and time consuming. A quicker method is to assume the visitor characteristics and types of use do not vary much by strata and simply total the observations directly (essential assuming the 30 observations are a representative sample). On spreadsheet, sum the columns to get total counts of all variables in the sample. Then simply divide by appropriate totals to estimate percent white vs non-white, male vs female, by age, etc. Be careful to make percents sum to 100% (due to some missing data, not all fields will sum to same total as PEOPLE column). For example, in getting percents by age divide each age group total by the sum of totals across all age groups. Note that you can put formulas at bottom of one column and simply copy them across to quickly compute all column sums or averages.
3. Comment on the accuracy of your results (confidence intervals? or discussion of errors).
HINTS ON ERROR AND CONFIDENCE IN RESULTS. You should try to convey to the client some idea of accuracy/error in the estimate of use. Some ideas here are: a) commenting on representativeness of sample (did we get a typical mix of weather patterns and reasonable time distribution within the strata), b) noting the amount of variation in use counts (highs and lows) and hence sensitivity to which periods we sampled, or c) a formal estimate of confidence using standard errors. (C) can be done by strata (need at least two observations in a stratum to estimate variance from sample). Some strata will have higher variances than others, so estimates of means for those strata will have more error.
If you want to take a crack at a confidence interval, I'd suggest trying it with sample as a whole first, ignoring strata. To do this, in Excel compute the standard deviation of entries in the PEOPLE column (STDDEVP function), then calculate standard error of mean as standard deviation/sqrt(n), n=30. Convert this to a percent of the mean by dividing the standard error by the PEOPLE mean. Now apply this percent error to your (expanded) estimate of October use from step 1. Remember two standard errors either side of mean is a 95% confidence interval, so take two "Pct errors" either side of mean. For example: If mean is 100 and standard error is 10, the percent error is 10% (10/100) . Two standard errors is 20% either side of mean. If expanded use estimate is 25,000, then a 95% CI is 20% either side of 25,000 or between 20,000 and 30,000. If this makes no sense to you at all, disregard and restrict your comments about error to a or b. A better, but messier approach is to compute standard errors of means for each stratum and sum confidence intervals across strata. - for this use same Pivot Table as in (1) above. First copy the Pivot table below using Paste Special - Values to copy the values in table. Then re-enter Pivot Table wizard and change middle to STDEVP of PEOPLE rather than AVERAGE - copy this next to averages below; finally change middle to COUNT of PEOPLE. Now divide standard deviation by square root of the count for each cell to compute standard error, divide into average for each cell to express it as a percent of mean.
Lansing Riverfront Trail Study
OBJECTIVES:
1. Estimate the amount of use on trail east of Potter Park during October 1996.
2. Estimate use by user characteristics and type of use (activity).
3. Describe temporal and spatial patterns of use.
APPROACH: Systematic observation.
POPULATION: All persons using the eastern sections of the trail during October, 1996 are included in the population of users. Users are defined as anyone physically present on the trail surface between the eastern trail terminus near Kalamazoo St. and the bridge on the trail over the Red Cedar River just west of Aurelius Rd.
The unit of analysis for sampling purposes is time blocks rather than people. We will sample from the population of one hour time periods in October at two access points. As trail access is limited on the eastern sections, we will use point measures of use to characterize each segment. Three segments will be studied :
Segment 1 : Eastern terminus at Kalamazoo St. to mid-way point along the trail toward the Aurelius access - use measured by visitor counts at eastern terminus.
Segment 2: Aurelius access point & eastward to same mid-point as above - measured by use at Aurelius access traveling to or from the east.
Segment 3: Aurelius access west to Potter Park - measured by use at Aurelius access traveling to or from the west.
The time period covered in the study is the month of October. Use will be recorded only for daylight hours, approximately a 12 hour period from 7:30 am to 7:30 pm each day in October. There are 372 one hour blocks in October during daylight (31*12).
SAMPLE: A clustered, stratified random sample of time periods/access points will be taken. The population is stratified by time and location. Use will be observed on a sample of 36 one hour blocks, 18 at Kalamazoo and 18 at Aurelius. Hours are divided into strata by weekend/weekday and morning, mid-day and late afternoon. Combining the hourly and day of week strata yields 6 time strata - we will try to observe 6 hours in each strata for a total of 36 observations. Observations in each stratum will be split equally between Aurelius and Kzoo.
SAMPLING STRATA
Morning7:30-11:30 am / Afternoon
11:30-3:30 / Evening
3:30-7:30 pm / Total
Weekday (M-F / 6 / 6 / 6 / 18
Weekend (Sat, Sun) / 6 / 6 / 6 / 18
Total / 12 / 12 / 12 / 36
COMPLETE THE FOLLOWING FORM BEFORE YOU BEGIN OBSERVING: ADD LAST LINE AT COMPLETION OF INTERVIEW PERIOD.
LANSING TRAIL OBSERVATION FORM:Location : KZOO AURELIUS
Observer ______Date : ______, October ______, 1996
(day of week) (date)
Weather conditions:
Temperature ______; Sunny Partly Cloudy Raining
Trail Conditions: Dry Wet
Begin Observation At ______am pm ; Number of Cars in lot at start ______.
End Observation At ______am pm Number of Cars in Lot at end ______.
COMMENTS:
OBSERVER INSTRUCTIONS:
1.Sign up for one of the sampling periods/locations.
2.Obtain observation forms and instructions and read these prior to observation period.
3.Report to the designated location with the observation form, a watch, pencil and clipboard. Find a comfortable location for observing where you have an unobstructed view of the trail.
4.Complete the first part of observation form entering your name, date and time you began interviewing, location, and weather conditions.
5.Record each trail user passing your station on a separate line. Circle appropriate items within each category . Enter a sequential user number in left column, i.e. 1,2,3,4,5,... See coding instructions below for details.
Time Periods: For this exercise we will give you some flexibility in choosing the time of interview to accomodate your schedules. You may choose a one hour period within the assigned time starting on the hour or half hour. For example, if you are assigned the 7:30-11:30 am block, you may choose any of the following one hour periods: 7:30-8:30, 8:00-9:00, 8:30-9:30, 9:00-10:00, 9:30-10:30, or 10:00-11:00. Normally the precise hour would be assigned to assure representation within the 4 hour blocks.
Observation Points
At Kalamazoo observe at trail entrance at far end of parking lot behind Steak House. You may be able to observe from your car or station yourself in vicinity of the entrance.
At Aurelius observe from trail immediately in front of parking area so you can observe entering, exiting and thu traffic. You may observe from the "grassy knoll", the fishing pier/boat ramp, or perhaps from car.
CODING INSTRUCTONS:
List each individual (including babies, but not pets) passing your position (or in the immediate vicinity) using the trail on a separate row. Enter a sequential user id number in left column. Complete the information for each individual in the remaining columns by circling the appropriate response in each column. In the left margin of form, mark a 2,3, and 4 at the beginning of the second, third, & fourth 15 minute period. We will want to generate counts for the hour and each 15 minute block. If you count more than 20, start on new page and number pages at top.
REPEAT TRAFFIC: When you can recognize the same individual or party returning to your interview point (once, twice, or several times), find that person on the list and make a second entry in the TRAVEL DIR column, e.g. if person was going E first time, circle W, If In, perhaps out or thru. If unsure about repeats, treat as a new visitor. You needn't record more than one repeat for each individual, although you should finish with exiting information if you observe the person leaving the trail after multiple passes of your observation point.
CODING BY VARIABLE:
ACTIVITY: Circle W(walk), J(jog), B(bike), RB(rollerblade), RS(rollerskate), RD(ride in backpack, stroller, wagon, bikeseat, etc.) . Write in any other activity - enter H for wheelchair users.
PETS: enter number of pets (leave blank if none). Assign pets to individual with leash or nearest to pet. Count strays (not with anyone) and record at bottom of pet column outside the margins.
TRAVEL DIRECTION:
Enter direction of travel and if the individual is entering trail, leaving trail or traveling thru to east or west (at Aurelius). Enter S (Stationary) for people hanging around access points, not traveling linearly along trail (e.g. anglers at Aurelius). Don't include people sitting in cars who do not get out.
At Kalamazoo - W = coming onto trail and traveling west along trail
E= leaving trail traveling in an easterly direction
S = stationary
At Aurelius - W= going toward Potter Park or exiting here and coming from the east
E = going toward Kalamazoo St or exiting from west (Potter).
Also circle one of following:
IN= entering trail here
OUT = leaving trail here
THRU = passing thru along trail (ie, not entering or leaving). At Kzoo this would be turning around and returning.
ACCESS: Indicate for those entering or leaving trail whether access to trail is on foot, by car, or bicycle. (e.g. if they load/unload bicycles into car check car).
AGE: Estimate age within broad groups as indicated. Circle the number for the age category.
RACE: Check White(W) or non-white (NW). Treat Non-white as an "other" category including blacks, native americans, asians, and hispanics. Circle ? if can't tell or unsure.
GENDER: Note male or female. Circle ? if unsure or you can't tell.
CAR COUNTS: At Kzoo count any cars toward back of lot (paved or dirt section). Don't count cars parked close to steak house.
OBSERVATION FORMPage ______
RECORD EACH INDIVIDUAL OBSERVED ON A SEPARATE LINE
ACTIVITY / PETS / DIRECTION- / ACCESS / AGE / RACE / SEX1 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW
? / M F
?
2 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
3 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
4 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
5 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
6 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
7 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
8 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
9 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW
? / M F
?
10 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
11 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
12 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
13 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
14 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
15 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
16 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
17 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
18 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
19 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
20 / W J B
RB RS RD / E W S
In Out Thru / Ft Car Bike / 2 6 13 18 30 60+ / W NW ? / M F
?
SUMMARY COUNTS (count number of trail users in each category during your hour of observation). These counts were transferred to Excel spreadsheet - one row for each hour of observation. The first 14 variables on Excel spreadsheet come from summary sheet above. Labeled "Lansing Trail Observation Form". The rest are counts made from the coding sheet.
DO NOT INCLUDE REPEATS in these Tablulations
CategoryNumber Observed
Total visitors______
By Activity:
Walk______
Jog______
Bike______
RB______
RS______
RD______
Other______
By Direction (Include repeats here)
East______
West______
South______
By In/Out/Thru (AURELIUS ONLY) - Include repeats here
In ______
Out______
Thru______
PetsNumber (Not entered in Excel)
By Access
Walk______
Car______
Bike______
By Age
<2______
6______
13______
18______
30______
60 ______
By Race
W______
NW______
By Gender
M______
F______